3330 Exam 2 Review Spring 2011
Chapter 8 Key Concepts
Eduardo Sixto
~Based on microfossils there is a two billion year diversification period
where cells created by abiogenesis, ~4.0-3.5 Bya, developed into the basis
for the eukaryotic cells, 2.5-2.8 Bya.
~The first successful protocells would have been heterotrophs. It is
assumed that after raw material become short on supply some of these cells
become photosynthetic autotrophs, cyanobacteria.
~Methane concentrations in ancient rocks suggest that some of the cells
produced methane as a byproduct from metabolic pathways.
~Stromatolites in the coast of Australia support the theory that life had
diversified 3.4 Bya and existed in structured, biological ecosystems.
~All organisms are bound by four essential facts1) they share a common
inheritance 2) their past has been long enough for inherited changes to
accumulate 3) the discoverable relationships among organisms are the result
of evolution 4) discoverable biological processes explain how organisms
arose and how they were modified through time by the process of evolution.
~The first two kingdoms recognized were Plantea, plants, and Animalia,
animals. This later changed to account the bacteria as another kingdom, the
Protista.
~In 1938 a proposed kingdom for bacteria and the blue-green algae was
called Kingdom Monera.
~In 1969 the fungi, classified as plants, were elevated into their own
kingdom, Kingdom Fungi.
~ Carl Woese, having performed genetic comparisons on different cell
species, was able to define three domains for the living world. The
Eubacteria, which include the bacteria and cyanobacteria, Archaea, the cells
that have cell walls made of different molecules from those found in bacteria
and cells which often live under more rigorous conditions, and the Eukarya,
which included slime molds, ciliates, and the multicellular kingdoms of the
Plantea, Animalia, and Fungi.
~Archaebacterial traits distinguishable from Eubacteria are the different cell
wall chemistry, membrane lipid chemistry, major nutrient metabolic
pathways, ribosomes and RNA polymerase and DNA associated with
histones, like Eukaryotes.
~The Last Universal Common Ancestor of all organisms today had DNA as
the hereditary material, DNA replication with helicase and DNA
synthetases, ribosome-based protein synthesis, several common metabolic
pathways, ATP, phospholipid bilayer cell membrane, and active transport
across membranes.
~Cyanobacteria fossils are the oldest fossils found in Western Australia from
about 3.5 Bya making it surprising due to the fact that the earliest rocks are
only dated back to 3.8 Bya.
~Cyanobacteria dominated the globe for 2 billion years, with some forms
still existing today. They produced large quantities of oxygen by
photosynthesis which would slowly eliminate the reducing atmosphere of
early earth.
~Eukaryotic cells probably arose through endosymbiosis and incorporation
(e.g. chloroplast, mitochondria).
~Horizontal Gene Transfer, HGT, is affective by a virus or a small,
circular DNA particle known as a plasmid that contains a foreign gene and
as much as one-third of some prokaryotic genome has been acquired through
HGT.
~Less than ten-percent of eukaryotes acquired one or two protein families
through HGT.
~The three main ways of prokaryote HGT are
1) Transformation, the up-take of naked DNA from the external
environment
2) Conjugation is the process by which one bacterium transfers genetic
material to another through direct contact. During conjugation, one
bacterium serves as the donor of the genetic material, and the other serves as
the recipient. They do not have to belong to the same species. The donor
bacterium carries a DNA sequence called the fertility factor, or F-factor. The
F-factor allows the donor to produce a thin, tubelike structure called a pilus
or conjugation tube, which the donor uses to contact the recipient. The pilus
or conjugation tube then draws the two bacteria together, at which time the
donor bacterium transfers genetic material to the recipient bacterium.
Typically, the genetic material is in the form of a plasmid, or a small,
circular piece of DNA of plasmid DNA, though in some circumstances, it
might be a part or all of the main bacterial "chromosome" or main circular
DNA genome.
3) Transduction, or transfer via viral infection.
~ prokaryotic HGT may be a beneficial process since they reproduce
asexually, but with HGT a cell can acquire a gene that confers survival or a
novel characteristic which enables them to thrive in harmful conditions or to
utilize a new metabolite. It is through this process that resistance to
antibiotics can be transferred from one bacterial cell to another.
~Another classic example for HGT is the origins of Mitochondria and
Chloroplast from endosymbiosis.
~Archaebacteria acquired organelles by endosymbiosis.
~Early Eukaryotes has cell walls, were aerobic heterotrophs, and eventually
developed sexual reproduction, which would lead to the decline of HGT
among Eukaryotic lineages likely to the alternative sexual recombination.
Chapter 8 People
Robert Ahlers & Nanci Macias
Two Kingdoms
 Aristotle (384-322 BCE) Greek Philosopher, student of Plato, Great
Chain of Being
Classified life into two kingdoms
Aristotle's Two Kingdoms:
 Plantae (L. planta, plant)
 Animalia (L. anima, breath, life)
 This classification lasted for more than 2000 years
Two Kingdoms becomes Three
 Carolus (Carl) Linnaeus (1707-1778) Swedish biologist, founder of
systematics
Clarified the Two Kingdoms of Life and recognized a third Kingdom
(1735)
Linnaeus' Three Kingdoms:
 Plantae
 Animalia
 Lapideum (minerals)
Charles Darwin (1809-1882) British naturalist, wrote On the Origin of
Species (1859)
 All true classification is genealogical
 Grand analogy: Evolution is a branching tree
 Only after his theory was published did biological evolution become
an acceptable alternative to earlier explanations
 Organisms change over time
Three Kingdoms of Organisms:
John Hogg (1800–1869)
Sir Richard Owen (1804–1892) British comparative anatomist
Ernst Haeckel (1834-1919) German naturalist, embryologist, artist (Art
forms in Nature)
Haeckel made the most extensive classification
Haeckel Three Kingdoms:
 Plantae
 Animalia
 Protista
Two Empires (Domains) of Organisms:
 Édouard Chatton (1883-1947)
Defined the terms ProKaryota and Eukaryota (1925)
The terms had little impact on classification for decades
Chatton's Two Domains:
 Prokaryotes (single-celled organisms)
 Eukaryotes (multi-celled organisms)
Three Kingdoms become Four Kingdoms
 Herbert F. Copeland (1902-1968)
-wrote The Classification of LOWER ORGANISMS (1956)
-Proposed a four-kingdom classification (1938)
-Moved the two prokaryotic groups---bacteria and "blue-green algae"--- into a separate
Kingdom---Monera
Copeland's Four Kingdoms:
 Monera (prokaryotes)
 Protista (primitive eukaryotes)
 Metaphyta (plants)
 Metazoa (animals)
Two Domains Became Five Kingdoms
(still 2 Domains- - -Prokaryotes and Eukaryotes)
 Robert Harding Whittaker (1920–1980) American plant ecologist
Elevated the fungi to their own Kingdom (1969)
Whittaker’s Five Kingdoms:
 Monera (prokaryotes)
 Protista (primitive eukaryotes)
 Metaphyta (plants)
 Metazoa (animals)
 Mycota (fungi)
Five Kingdoms Became Three Domains
 Carl Woese (1928 - ) American microbiologist, wrote The Genetic
Code (1967)
-Catalogued presence/frequencies of various sequences in the 165
rRNA components of
ribosomes in representataives of the 3 Kingdoms.
-Determined archaebacteria should be placed in separate domaindefined Archaea
-3 Domains with 5-6 nested Kingdoms
Woese's Three Domains:
 Eubacteria (Bacteria) - prokaryote (lacking a nucleus or other
membrane-bound organelles) unicellular organisms with cell walls
which include peptidoglycan and may be distinguished by the Gram
stain (positive, negative, or variable); most are heterotrophic and some
are photosynthetic, a minority are chemotrophic. Most are either
coccal (spherical), rods, or spiral forms
 Archaea (Archaebacteria) - prokaryote (lacking a nucleus or other
membrane-bound organelles) unicellular organisms with cell walls
which lack peptidoglycan and are not easily distinguished by the
Gram stain; they may be heterotrophic, photosynthetic, or
chemotrophic. Some live in extreme environments. They are the
sister group to Eukarya because they use histone proteins in their
DNA supercoiling.
 Eukarya (Eukaryota)
Five Kingdoms become Six
 Thomas Cavalier-Smith (1942- ) published extensively on the
classification of protists, wrote Predation and Eukaryote Cell Origins:
A Coevolutionary Perspective (2008).
-Has been tinkering with the classification for more than a decade and
his taxa remain controversial--he rejects the three-domain system
entirely.
-Divided the domain Eukaryota into nine kingdoms. (1981)
-Reduced the total number of eukaryote kingdoms to six. (1993)
-Classified the domains Eubacteria and Archaebacteria as kingdoms,
adding up to a total
of eight kingdoms of life (Plantae, Animalia, Protozoa, Fungi,
Eubacteria,
Archaebacteria, Chromista, and Archezoa)
-His classification treats the archaebacteria as part of a subkingdom
of the Kingdom
Bacteria (2004)
Cavalier-Smith's Six Kingdoms (2004):
 Bacteria
 Protozoa
 Chromista
 Plantae
 Fungi
 Animalia
Chapter 9 People Study Guide
Patrick Arevalo & Isabel Torres
Lynn Margulis (1938- )
a. American Biologist who was born on March 5, 1938
b. University Professor in the Department of Geosciences at
the University of Massachusetts Amherst
c. She helped proposed endosymbiosis
i. Used to explain the origin of mitochondria and
chloroplasts
Thomas Cavalier-Smith
d. Born on October 21, 1942
e. Professor of Evolutionary Biology at the University of
Oxford
f. He proposed the taxa of Rhizaria in 2002.
Shama Barnabas 1982
 Along with fellow co-workers produced a tree of life that took into account the nucleotide sequences
from 5s rRNA and amino sequences.
 This phylogeny provided strong support for the Symbiotic theory of organelle function
Chapter 9 Review
Kelly Anderson & Isabel Torres
Concepts and Vocabulary
Evolution of Eukaryotes
 As early as 1.5 Bya eukaryotic cells appear as fossils
 Early eukaryotes were single-celled organisms or simple
filaments
 Today, most eukaryotic cells are multicellular and all contain a
nuclear membrane and organelles
 Kingdom Protista: all unicellular eukaryotes. Probably not
monophyletic
 Endosymbiotic events provided mitochondria, chloroplasts
 Microtubules drive the nuclear chromosomal division (mitosis)
Five Eukaryotic Supergroups
 Plantae (Archaeplastida): Charophyta (stem group), red algae,
green algae, and land plants
 Excavata:
o Various Protistans
o many with parasitic lifestyles
 Giardia, Trichomonas, Trypanosoma
 Chromalveolata:
o first proposed by Thomas Cavalier-Smith
o algae, heterotrophic ciliates, water molds, dinoflagellates,
diatoms
o protistan parasites
 Plasmodium falciparum
 Rhizaria: advocated for by Cavalier-Smith.
o Heterotrophic protistans
 Foraminiferans, radiolarians
 Unikonta:
o Parasitic Protistans, choanoflagellates, fungi, animals, and
Amebozoans (slime molds), amoeba
The two popular theories to explain the origin of the membrane bound
organelles
 Endosymbiosis - a well supported hypothesis which explains the
origin of chloroplasts and mitochondria and their double membranes;
This concept postulates that chloroplasts and mitochondria are the
result of many years of evolution initiated by the endocytosis of
bacteria and blue-green algae. According to this concept, blue green
algae and bacteria were phagocytized but not digested; they became
symbiotic instead and subsequently co-evolved with considerable
horizontal gene transfer between the nuclear and organelle genomes.
Other data supports an endosymbiotic origin for the eukaryotic
nucleus.
 Invagination – the plasma membrane was engulfed or invaginated to
form the endomembrane system.
Along with the theories above, were two models explaining the origin of the
Eukaryotes, the Nucleus First-Mitochondria Later Model and the
Mitochondria-Nucleus Co-origin model.
Origin of Eukaryotes
 Endosymbiosis: When ancient anaerobic eukaryotic cells
engulfed prokaryotic organisms and established a symbiotic
relationship with the prokaryote. The prokaryotes were retained
as cellular organelles – mitochondria and chloroplast – providing
eukaryotes with additional sources of DNA.
 Free-living bacteria developed mutually beneficial relationships
within a host prokaryotic cell
 Aerobic bacteria developed into mitochondria
 Cyanobacteria developed into chloroplasts
Organelle DNA differs from Nuclear DNA
 Location: organelle vs. nucleus
 Organization: singular circular vs. multiple linear strands
 Function: Which proteins coded for and how regulated
 Mode: of replication and inheritance
Mitochondrial DNA
 Single double-stranded DNA molecule
 Many mitochondria in each cell
 Similar to prokaryotic DNA because no histones or proteins, and
no introns
Chloroplast DNA
 single double-stranded circular DNA
 inherited uniparentally from the maternal (seed) parent
 1/4th of DNA of cell
Origin of Various Photosynthetic Eukaryotes
 The origin of early eukaryotic ancestors leading to the lineages of
animals and fungi was probably and independent event from that
of the origin of plants
Transfer of Genes Between Organelles and Nucleus
 Many transferred back and forth
o Ex: genes for amino acid synthesis
 Improve efficiency and reduce mutations
 Genes transferred to and from the eukaryotic nucleus are a form
of Horizontal Gene Transfer
o Complicated the establishment of phylogenies
The Molecular Clock: uses mutation rates to estimate evolutionary
time
 Mutations at a given locus add up at a constant rate in related
species
o This mutation rate is the ticking of the molecular clock
o As more time passes there will be more mutations at a
relatively constant rate
o Each DNA sequence or polypeptide product will exhibit its
own "clock" speed because mutation rates vary
 Mutation rates are estimated by linking molecular data and real
time from the fossil record
o Higher rates are better for closely related species
o Lower rates are better for distantly related species
Organelle DNA as a Molecular Clock
 The Molecular Clock is a powerful tool for estimating the dates of
lineage-splitting events
Mitochondrial DNA and Ribosomal RNA
 Different nucleic acid molecules or gene loci have different
mutation rates
 Ribosomal RNA used to study distantly related species
o Lower mutation rates that most DNA
 Mitochondrial DNA is used to study closely related species
o 10 x faster mutation rates than nuclear DNA
o Passed down from other to offspring, so it is not subject to
recombination, making it easier to trace.
Using DNA as a Molecular Clock
 Easy to use DNA from living species to draw conclusions about
phylogeny and times of divergence
 Harder to use DNA from fossils and museums because probable
contaminated by other DNA and only have small amounts of DNA
Eukaryote Characteristics
 DNA organized as linear chromosomes
 Many cytoplasmic membrane-bound organelles
 Eukaryotic cytoskeleton and ribosomes
 Presence of external cell wall variable
 Sexual reproduction predominates, various means of gene
recombination
 Unicellular or multicellular
Eukaryotic Cell Plant
 Same basic components as the animal PLUS:
o cellulose cell wall
o central vacuole (sequesters various chemicals)
o chloroplasts that carry out photosynthesis
Eukaryotes package DNA differently
Transcription and Translation in Prokaryotes and eukaryotes
 prokaryote genes lack:
o introns, no pre-mRNA processing
o No nucleus, no separation between DNA and cytoplasm
o Methods of gene regulation differ
Gene Expression
 DNA contains a sequence of nitrogenous bases which codes for
the sequence of amino acids in a protein
 Triplet code: each code is composed of 3 nitrogenous bases (A, C,
G, or U in mRNA) from genetic code
 During transcription
o 1 strand of DNA serves as a template for formation of mRNA
 Messenger RNA is processed with intron removal, before leaving
the nucleus
 (note*the bases of mRNA are complementary to the base sequence of
DNA)
 mRNA carries the codon sequence to the ribosomes (ribosomal
RNA and protein) in the cytoplasm
 Translation: mRNA codons determine the order of tRNA peptide
bond formation
 produces primary structure of protein at the ribosome
Oxidative Nutrient Metabolism
 Breakdown products of carbohydrates, fats, and proteins enter
various metabolic pathways where energy is harvested
 Oxygen is used up, Carbon dioxide is given off
Nutrient Catabolism Pathways are all Interconnected
Photosynthesis
 Sunlight + 6H2O + 6CO2  C6H12O6 (nutrient sugars)+ 6O2
o autotrophic prokaryote, protistan and plant cells contain
various membrane-bound photosynthetic pigments
(phycobilins, caretenoids, and chlorophylls) which can trap
light and convert light energy to chemical energy (ATPs and
NADP+s). light energy drives one of three independent
forms of atmospheric CO2 capture (C3 carbon fixation, C4
carbon fixation, and Crassulacean Acid Metabolism);
photosynthetic eukaryotes contain chloroplasts as the
organelles of photosynthesis. The derived chemical energy
also powers the light independent Calvin cycle which
generates the glucose which may be used in cellular
respiration and starch synthesis.
Landmarks in Time
 Around 2.0 Bya: eukaryotes develop from prokaryotes by complex
means including endosymbiosis and develop sexual reproduction
and colonial life forms
 Around 1.8 Bya: O2 levels rise sufficiently that the atmosphere
becomes oxidizing
 Around 1.3-0.6 Bya: multicellular (metazoan) life evolves (several
times?)
Chapter Ten Plants
Ashley Schmidt & Trent Gaasch
Important Facts:
 Land plants evolved from organisms similar to some living
green algae some ~460 Mya
 Leaves and multicellularity evolved many times
 Fungi are not simple plants but a sister group of animals
 Many of the adaptations of land plants reflect the transition
from water to land.
 Horizontal gene transfer, endosymbiosis, differentiation of
somatic and germinal tissues, and mechanisms of
fertilization were important in plant evolution.
Kingdom Viridiplantae:
o Includes land plants and green algae ( red and brown algae
excluded)
o All green plants appear to be derived from a single species
of freshwater algae.
o All green algae can be split into two major clades:
1.) Chlorophytes: exclusively aquatic
2.) Charophytes: aquatic forms which gave rise to the
land plants
General Information about plants
 Multicellularity probably began when dividing cells
stopped separating after mitosis and cytokinesis
o Advantages include increased size and opportunity
for cell differentiation and specialization
 Multicellular organisms then evolved into forms in which
most cells were somatic while a few were reproductive,
forming gametes by meiosis
 Using 18S rRNA, rbcL (ribulose-bisphosphate
carboxylase gene), and nuclear and mitochondrial
genomes sequences, investigators demonstrated that
numerous lineages of aquatic algae invaded the land
 Transformation of one of these lineages gave rise to two
major lineages:
o chlorophyte green algae
o charophyte algae and the land plants
Alternation of generations - The occurrence in one species' life history
of two or more different forms differently produced, usually an
alternation of a sexual form using meiosis to generate recombinant
gametes with an asexual form using mitosis to generate identical clonal
offspring in the life cycle of a multicellular plant or animal. In land
plants, the asexual form/tissue is composed of haploid cells and the
sexual form/tissue is composed of diploid cells. In the earliest evolved
land plants (bryophytes), the haploid sporophyte tissue was dominant,
i.e., it was the tissue of the individual that persisted throughout life
while the diploid reproductive tissue formed a temporary additional
structure during periods of sexual reproduction which were often times
of environmental stress. In the later derived land plants, primarily the
ferns, gymnosperms, and angiosperms, the diploid sporophyte tissue is
dominant, and the gametophyte tissue is reduced to small numbers of
temporary cells that exist only during the time for fertilization, e.g.,
ovules and polar bodies in females, and pollen grains and pollen tubes in
males.
The four major plant groups are
1.) Seedless non-vascular plants- these are plants with no seeds
or veins. These are the simplest plants; they have limited
distribution and are restricted to wet areas, and collectively
known as bryophytes (liverworts, club mosses, and
hornworts). They the first fossil evidence is of them appeared
to date back to 420Mya in the Devonian period, and then later
in the Carboniferous 350Mya ago. They major importance of
bryophytes is that they represent the beginning transition
from water and the dominance of a diploid sporophyte life
cycle.
a. Bryophytes:
i. The “simplest” land plants, limited to moist
environments, are bryophytes
ii. Liverworts at 420 Mya;
iii. Mosses at 350 Mya
iv. Bryophytes were important in two major
transitions:
1. water to land;
2. haploid gametophyte-dominated life cycle
to a diploid sporophyte-dominated life
cycle.
Vascular seedless plants- the evolution of the cambium permitted
plants to increase in size. The cambium is the tissue from which new
cells are produced to increase the diameter of plant stems. This allows
plants to grow taller allowing them to receive more light and nutrients
through xylem and phloem tubes. These plants reproduce by using
spores which need to be spread by the environment. One of the most
common plants in this group is ferns. Ferns are also the first vascular
plants with true leaves.
1.) Gymnosperms- are plants which contain cones or
alternatives to seeds contained in true fruits. These are plants
such as ginkgo, cycads, and cypress trees.
a. Gymnosperms are plants with “naked seeds”
i. Ovule is exposed on a scale at pollination
b. There are four living groups
i. Coniferophytes
ii. Cycadophytes
iii. Gnetophytes
iv. Ginkgophytes
c. All lack the flowers and fruits of angiosperms
d. Probably descended from progymnosperms
i. Seeds had evolved by end
of Devonian period
ii. Adaptive radiation in
Carboniferous and early
Permian produced the
gymnosperm divisions
iii. Largely replaced seedless
vascular plants
iv. Better adapted to drier
(Pangean) climate
2.) Angiosperms- these are flowering plants and also closely tied
to dicots, which have two seed leaves. These plants have
elaborate flowers which are used as reproductive organs
which can be specific to certain animal pollinators or open to
any pollination method.
a. Their origin is a mystery
b. Evolution and elaboration of flowers as reproductive
organs
c. Evolution of diverse flower structures that enable
insects, birds, and less often other animals to pollinate
them
d. Evolution of diverse seed forms and mechanisms of
dispersal
e. Life Cycle
i. The double fertilization in Angiosperms to
produce the nutritive triploid (3N) endosperm is
the pinnacle of advanced parental care in plants
ii. It is comparable to the cleidoic egg of reptiles,
birds, and montremes, and then the intrapouch
and intrauterine development of embryos seen in
the marsupial mammals
iii.
1. Mitotic division produces embryo
a. Rudimentary root
b. One (monocots) or two (dicots) seed
leaves
iv.
1. Mitotic division produces energy-rich
endosperm
2. Ovule matures into a seed
v. Why double fertilization?
1. Synchronizes development of food storage
with seed development
2. Without fertilization,
neither will occur
a. Resources are not wasted
on infertile ovules
Origin of leaves- the origin of leaves has two good hypotheses:
1.) The telome hypothesis which says leaves arose from webs
between flattened branches.
2.) The enation hypothesis which says leaves arose from small flaps
or extensions of tissue along the stem.
*We know that leaves evolved multiple times therefore, either of the
two modes for the origination of leaves can explain how the may
have developed between different lineages.
Transitions for plants:
 Origin of the land plants (embryophytes)
o Land Plant Phylogeny
o
 Origin of the vascular plants (tracheophytes)
o Early Vascular Plants
 “Vascular” refers to the presence of conductive tissue:
 xylem that enables water to reach the erect
parts of the plant;
 phloem that enables nutrients to be distributed
from the leaves and stems.
 Cooksonia, the first vascular land plant, appeared
about 420 Mya
 -Only a few centimeters tall

-No roots or leaves

-Homosporous
 Origin of the seed plants (spermatophytes)
 Origin of the flowering plants (angiosperms)
Plant Life Cycles
As more complex land plants evolved:
1.) The spores became unequal in size
2.) The diploid stage became the dominant portion of the life cycle
3.) The gametophyte became more limited in size
4.) The sporophyte became nutritionally independent
These changes, along with improvements in morphology allowed
radiations into drier habitats
Moving onto Land
 Three evolutionary changes:
o reduction in the size of the gametophyte
o evolution of easily dispersible pollen
o and encasement of spores in seeds
 Allowed plants to avoid desiccation and so move away from water
Flower population mechanisms:
 In order for a flower to be pollinated, pollen must be moved from
the anthers to the stigma of the same or different flowers
 Whatever moves or carries the pollen is called a vector.
 There are five different classes of vectors:
o wind / water / insects /
mammals / birds
 Flowers and the animals which pollinate them have often evolved
very close relationships in which both are totally reliant on each
other
 The plant for reproduction, the vector for some aspect of it
biology, often nutrition
Chapter 10 Plants: Part two
Dani Joslin and Ashley Schmidt
Angiosperms- evolution and elaboration of flowers as reproductive
organs, evolution of diverse flower structures to allow insects, birds and
other organisms to pollinate them, also evolution of diverse seed forms
Sperm plus egg equals diploid zygote
1. Mitotic division produces embryo
Sperm plus nuclei equals 3n nucleus
1. Mitotic division produces energy rich endosperm
2. Ovule matures into a seed
Double Fertilization
1. Why? Synchronizes development of food storage with seed
development
2. Without fertilization neither will occur
Angiosperm radiation1. Radiation of angiosperms marks the transition from the Mesozoic
era to the Cenozoic era
2. Adaptive radiation made angiosperms the dominant plants on
earth by the end of the cretaceous
Convergent Evolution Produces Ecological Equivalents
1. Cacti from all different places
Coevolution1. Plant-pollinator coevolution is responsible for the diversity of
flowers
2. The pollinator gains nectar, and pollen and the plant gains cross
pollination
Coevolution- Plants have influenced the evolution of animals and vice
versa
Darwin and coevolution1. Darwin hypothesized that a hawk moth with a long proboscis would exist to pollinate the
Madagascar star orchid, a century later such a hawk moth was found
Fungi1. First appeared along with the first vascular plants in the Silurian
Fungi- are not simple plants, share an ancestor with animals, are more
closely related to animals than plants
Characteristics1. Eukaryotic, non-photosynthetic, some are parasitic, uni or
multicellular, avascular
2. Have an alternation of generations life cycle, reproduction by
spores or asexually, non-motile usually, decomposers and
recyclers of nutrients in environment
3. Absorptive heterotrophs, release digestive enzymes to break
down organic materials or their hosts, store food energy as
glycogen, build complex carbohydrate cell walls
4. Some are internal or external parasites, a few of them act like
predators and capture prey like roundworms
5. Some are edible and some are poisonous
6. Produce both sexual and asexual spores, classified by the
sexual reproductive structures, some have no sexual phase
7. Penicillin is made by the penicillium mold
Reproductive structures1. Basidia, sporangia, and asci
2. Spores consist of- haploid cell, dehydrated cytoplasm, protective
coat
3. Spores germinate when they land on a moist surface
Classification by nutrition1. Saprobes are decomposers and mold or mushrooms
2. Parasites- harm host, rusts and smuts
3. Mutualisms- both benefit, lichens and mycorrhizas
Major groups of fungi
1. Basidimycota- club fungi
2. Zygomycota- bread molds
3. Chytridiomycota- chytrids
4. AM fungi- arbuscular mycorrhyizas
5. Ascomycota- sac fungi
6. Lichens- symbiosis
Lichens- mutualism between fungus, algae and they form a thallus or
body
Chapter 11: People
Meghan Garrett & Megan Snyder
Richard Owen (1804-1892): An English biologist, comparative anatomist,
paleontologist who coined the term Dinosauria. Owen wrote Archetype and
Homologies of the Vertebrate Skeleton (1848) and On the Nature of Limbs
(1849). He regarded the vertebrate frame as consisting of a series of
fundamentally identical segments, each modified according to its position
and functions. This was an early attempt to argue for constraints on
organismal design from purely physical, mechanical, chemical principles.
Owen remained anti-Darwinian until his death.
Sir William D’Arcy Thompson (1860-1948): A scientist who advocated
structuralism as an alternative to survival of the fittest in governing the form
of species and also argued for constraints on organismal design. D'Arcy
Thompson 's most famous work was On Growth and Form (1917). The
central theme of On Growth and Form is that biologists of the early 20th
century overemphasized evolution as the fundamental determinant of the
form and structure of living organisms, and underemphasized the roles of
physical laws and mechanics. On the concept of allometry, Thompson
wrote: "An organism is so complex a thing, and growth so complex a
phenomenon, that for growth to be so uniform and constant in all the parts as
to keep the whole shape unchanged would indeed be an unlikely and an
unusual circumstance. Rates vary, proportions change, and the whole
configuration alters accordingly."
William Bateson (1861-1926): A British geneticist and a Fellow of St.
John's College, Cambridge. He was the first person to use the term genetics
to describe the study of heredity and biological inheritance, and the chief
populariser of the ideas of Gregor Mendel following their rediscovery in
1900 by Hugo de Vries and Carl Correns. He was the first to recognize
homeotic mutations and coined the term in his book Materials for the Study
of Variation (1894).
David Raup (1966): An American paleontologist and paleobiologist who developed such an approach to
plot the morphologies of organisms in the three dimensions in what he termed morphospace, which he
represented as a cube with different features of organisms along each axis. Raup’s analysis showed that the
known morphologies of shelled invertebrates cluster in one region of morphospace, a cluster that demarks
the limits of the body plan in these organisms and that not all forms were found in nature. Raup concluded
that unoccupied morphospace represented impossible morphologies, nonadaptive morphologies and/or
constraints on morphology
François Jacob: Wrote a paper, in 1977 that is credited with enticing many
researchers into molecular biology, that proposed gene regulation as
critically important in development, in evolution, and as a target for natural
selection.
Joseph L. Kirschvink: Originator of the snowball earth concept in 1989, a self-reversing climate instability
driven by ice-albedo feedback.
Adolf (Dolf) Seilacher: A German paleontologist who placed Ediacaran organisms into a distinctive group,
the Vendozoa, which he and others regard as unrelated to any animals; a separate evolutionary experiment.
Guy Narbonne: A Canadian paleontologist who invoked repeated structure based on fractal repeats of a
frond structure in his analyses of early Ediacaran organisms to identify a major group which he named
rangemorphs. Narbonne is cautious when it comes to saying whether rangemorphs were animals or an
alternative (and earlier evolutionary experiment in multicellularity.
Ch 11 Key Concepts and Vocabulary
Kayleen Parker
Key Concepts:
 The entire earth was encased in a sheet of ice 1 km thick two to four
times between 725 and 635 Mya. (Snowball Earth)
 Communities of enigmatic organisms -- the Ediacaran / Vendozoan
Biota -- existed in the Upper Precambrian more than 565 Bya,
before animals appear in the fossil record.
o Formed complex ecosystems.
o Disappeared early in the Cambrian.
 Based on molecular evidence we can conclude that animals originated
in the Precambrian 700-750 Mya.
 Animals of all major phyla first appear as fossils 545 Mya in the Early
Cambrian Burgess Shale and equivalent faunas worldwide.
 Stem taxa of animal phyla therefore must be Precambrian in age.
 Reasons for the origination of animals include the elaboration of
genes and embryonic development, environmental and climate
changes in the level of atmospheric oxygen.

Bauplan concept: placed more emphasis on the physical and
chemical restraints on organisms and how that forced them to evolve a
certain way

Types of temporal bone openings:
o Anapsid- ancestral form with holes only for the eyes and
nostrils( turtles)
o Synapsid- form that has one other hole besides the ones for the
eyes and nostrils (mammals)
o Diapsid- form that has 2 other holes besides the ones for the
eyes and nostrils (crocodilians, birds and dinosaurs)
 Homeobox genes that pattern animal bodies originated before
animals, plants, and fungi arose. They encode for transcription
factors.
 About 5545 Mya in the Early Cambrian, an explosive radiation of
multicellular organisms with soft and hard tissue appears in the fossil
record.
 Multicellularity facilitated cellular specialization within organisms
and structural differences between organisms, the evolution of
different modes of food gathering, and enormous increase in body
size.
 Some explanations to how animals radiated and diversified so
quickly:
o A rise in atmospheric oxygen
o Changing geological features
o Recovery from snowball earth
o Origination or elaboration of embryonic development
o Diversification of mechanisms of gene regulation
o The evolution of predator-prey interactions associated with the
opening up of new ecological zones
 Animal origins:
o choanoflagellates are ~150 living species (no fossils) of singlecelled and colonial protistans (the collared flagellate cell
morphology is similar to the choanocytes (collared cells) of
sponges and ribbon worms); they are motile predators who
were either animal ancestors or choanoflagellates and animals
descended from a common protistan ancestor; their
synapomorphies include certain cell adhesion molecules.
o The absence of features usually associated with prey capture,
and the absence of digestive tracts, led to proposals that many
Ediacaran / Vendozoan organisms may have depended on
photosynthetic or other types of symbiosis with
microorganisms.
o The organisms in the Ediacaran / Vendozoan Biota did not have
larval forms, eyes, mouths, anuses, intestinal tracts, or
locomotory appendages.
 Characteristics of animals:
o Eukaryotic, never photosynthetic
o Multicellular, usually with differentiation into tissues; avascular
and vascular forms
o Life cycle lacks alternation of generations
o No cell walls
o Sexual and asexual reproduction by often complex structures
and life cycles
o Enhanced responsiveness and motility due to nervous,
endocrine, and musculoskeletal systems
 Animals arise:
o By the beginning of the Cambrian 545 Mya, many different
types of animals were present, recognizable, and can be
classified on the basis of their different body forms.
o Burgess Shale Fauna:
 A 545 My old limestone reef assemblage of superbly
preserved fossils located in British Columbia, Canada at
160 m deeps and more than 20 km long and which
records the Cambrian Explosion of animal body forms.
Includes arthropods, sponges, brachiopods, polychaete
worms, echinoderms, cnidarians, and mollusks.
o 3 important conclusions to assign organisms from Burgess
Shale to clades:
 These organisms are crown taxa that already had evolved
the characters that define the phyla of living animals.
 Morphological gaps separated these crown taxa.
 Origination of phyla from stem taxa has to be sought in
earlier form in older deposits.
 The only evidence we have to recognize and classify Early Cambrian
organisms is morphological.
o One class of morphological evidence comes from the
preservation of cleavage-stage animal embryos in Late
Precambrian and Early Cambrian rocks.
 While not numerous, these specimens have given us a
glimpse of jellyfish development 530 Mya, and of the
presence of segments in early embryos.
 The absence of any fossilized larval stage strongly
suggests that early animals developed directly without a
larval stage (direct development).
 A Cambrian “Explosion”
o The diversity of Cambrian organisms could be interpreted as
adaptive radiation in which many new ecological opportunities
were made available for organisms with the capacity to evolve
in diverse ways so as to occupy and exploit the changing
environments.
o Divergence among major Cambrian lineages began in the
Precambrian about 700 Mya.
o Modifications during the Cambrian added hard parts and
mineralized skeletons that provided leverage for evolving
muscles, support for body organs, enclosures for gills and
filtering systems, and protective shells and spines.
 Causes of the Cambrian Radiation:
o Geological, environmental and climatic conditions
o Changing oxygen levels
o Predator-prey relationships
o Evolution of embryonic development and body plan
specification
o New sources of genetic variation and changes in gene number
and regulation
 Geological conditions:
o Animal fossils may be absent from Precambrian rocks because
geological conditions prevented fossilization or destroyed and
fossils present; the heat and pressure involved in Precambrian
mountain building has been proposed as an important factor
limiting fossilization.
 However, prokaryotic and eukaryotic organisms were
preserved in the Precambrian so it is unlikely that the
Cambrian discontinuity is unreal and merely the
consequence of geological metamorphism or imperfect
fossilization.
o Plate tectonics and sea level changes would also have played a
role in new environments.
 Rising Oxygen Levels
o Oxygen forms a protective blanket of ozone that could have
facilitated the expansion and radiation of multicellular animals
in shallow waters, tide pools, and nearby rocky surfaces.
o Aerobic metabolism, which is dependent on oxygen,
facilitated the use of new sources of energy, permitting increase
in body size.
o Animals capable of exploiting Early Cambrian oxygen would
have possessed a battery of common genes including those for
hemoglobin, which is a conveyer of molecular oxygen.
 Predator-prey relationships
o There was a change in the modes of feeding facilitated by rising
oxygen levels.
o Predators feed on the most abundant prey species, reduce the
numbers of prey, and so allow other species to use resources
formerly monopolized by the dominant prey.
o
Crucial Vertebrate Transitions:
o
origin of jaws
o
o
o
o
o
o
origin of fins and later
limbs for locomotion
origin of the lungs
origin of the cleidoic egg
origin of the advanced
water conserving
vertebrate kidney
two separate origins of
endothermy and
associated insulation
origin of pouch or
placenta for embryo
support and protection
 Shared Embryonic Development and Body Plan Specification
o Most distinctive morphological features of almost all adult
animals:
 Axes of symmetry, usually anterior-posterior (A-P),
dorso-ventral (D-V), and left and right (L-R).
 Paired appendages
 Similar tissues and organs
 Homeobox genes
o Contain the homeobox
o Each homeobox gene codes for a polypeptide sequence about
60 amino acids long called a homeodomain.
 Major conclusions from studies of comparative gene structure and
function:
o These important developmental (regulatory) genes all share a
common, highly conserved, and evolutionary ancient role as
transcription factors.
o A common genetic evolutionary origin underlies the
conservation of the basic developmental pathways that establish
animal body plans.
o What has changed with evolution is context; the specific
function of these conserved regulators varies from cell lineage
to cell lineage, tissue to tissue, organ to organ, as well as from
time to time during development.
 Mammalian Shared Derived Characters
o Endothermy with insulating hair and subcutaneous fat
o Mammary glands; extended parental care
o Uterus and colon (no cloaca)
o Dentary-squamosal jaw joint
o 3 ear ossicles
o Expanded cerebral cortex
o Heterodonty and buccal cavity (cheeks)
Vocabulary:
1)
Ediacaran Fauna / Ediacaran Biota- multicellular organisms
that remain enigmatic.
2)
Archaeopteryx- the 'missing link' that shows a transitional stage
between birds and dinosaurs
3)
Heterodonty- applies to animals that possess more than one type of
tooth morphology
4)
Ichthyosaur- giant marine reptile that lived during the Mesozoic era.
Developed from land reptile that made the transition back into the
water.
5)
Biota- a more appropriate term for the organisms found in a region or
a geographical period.
6)
Fauna- refers to the animal life found in a region or a particular time.
7)
Stem taxa-the earliest representation of a lineage. There can only be
one stem taxon for a lineage.
8)
Crown taxa- the terminal branches of a lineage arising from a stem
taxon. A single lineage may have more than one crown taxon.
9)
Vendozoa- a distinctive group of Ediacaran organisms that are
regarded as unrelated to any animals.
10) Modularity-concept
that units of life, such as gene networks,
aggregations of cells and organ primordial, develop and evolve as
units (modules) that interact with other modules.
11) Fractal-a shape that can be split into parts each of which has the same shape as the original (a fern
leaf).
12) Rangemorphs-existed in complex ecological communities with more than one trophic level with
frond-like organization 570-575 Mya.
13) Monoblastic
animals - show the simplest metazoan organization,
having a single germ layer such as sponges. Although they have
differentiated cells, they lack true tissue organization.
14) Diploblastic
animals - members of the phyla cnidaria and ctenophora
show an increase in complexity, having two germ layers, the
endoderm and the ectoderm organized into recognizable tissues.
The embryonic ectoderm develops into the epidermis, nervous system,
and, if present, nephridia; the embryonic endoderm develops into the
gut and associated glands.
15) Triploblastic
animals - possess a mesoderm as well as the endoderm
and ectoderm. They are the remaining animal/metazoan phyla from
flatworms to birds and mammals, most of which show bilateral
symmetry. They develop recognizable organs. The embryonic
ectoderm develops into the epidermis and its derivatives, nervous
system; the embryonic endoderm develops into the gastrointestinal,
respiratory and urinary tract and their associated glands, the secretory
cells of the endocrine glands, and the auditory system; the embryonic
mesoderm develops into body cavity linings, if present, mesenteries,
parts of the reproductive system, musculo-skeletal systems, blood
vessels and blood cells, the kidneys, the adrenal cortex, and the dermis
and other connective tissues.
16) The plankton explosion-a marked increase in size, diversity, ornamentation and turnover rate
among eukaryotic plankton (acanthomorphic acritarchs), which is tentatively attributed to
predation by eumetazoa.
17) Morphospace-3-D
representation of the morphological characters of
an organisms or group of organisms used to show how much of the
possible range of morphologies is expressed.
18) Protostomes
- the majority of triploblastic coelomate invertebrate
metazoans other than echinoderms, most of whom show bilateral
symmetry, a clade of organisms whose embryonic blastopore becomes
the mouth of the adult.
19) Deuterostomes
- the majority of triploblastic coelomate metazoans,
the echinoderms, chaetognaths, hemichordates, and chordates, most of
whom show bilateral symmetry, a clade of organisms whose
embryonic blastopore becomes the anus of the adult.
20) Acoelomates-no
true body cavity (flatworms)
21) Pseudocoelomates
- triploblastic metazoan animals which possess a
"false" body cavity, in which a fluid-filled cavity is only partially
bounded by mesodermal tissue; lacking any mesenteries to support
internal organs; and no muscular layers around the gut tube to provide
peristalsis; examples include round worms and some other protostome
invertebrates.
22) Coelomates
- triploblastic metazoan animals which possess a true
body cavity lined with a mesodermal lining; having internal organs
suspended in mesenteries; and muscular layers around the gut tube to
provide peristalsis during digestion; examples include most bilaterally
symmetrical animals, most invertebrates and the chordates
23) Cephalization-an
evolutionary trend in which nervous tissue becomes
concentrated toward one end of an organism, eventually producing a
head region with sensory organs.
24) Co-evolving
arms race-successive rounds of selection for predator
responses to their prey’s protective devices, followed in turn by
adaptations by the prey to their predator’s devices, promoting
diversity.
25) Homeobox
genes - any of the evolutionarily conserved genes which
are translated into embryonic regulatory (homeo)proteins that act as
DNA binding transcription factors that provide the primary signals
and initiate the pathways in animals that help differentiate bands and
clusters of cells that organize the pattern (anterior/posterior,
dorsal/ventral, right/left) of body regions and the formation of
particular structures such as internal organs, and body extensions,
sense organs, antennae, wings and legs, etc. They exist and play
similar roles in the development of higher plants and fungi.
26) Morphogens-
activate pathways leading to the development of an
organism’s form or part of an organism.
27) Antennapedia
complex-cluster of six Antennapedia-linked genes
first discovered in fruit flies whose activation converts anterior into
posterior body structures.
28) Homeotic
mutations (homeosis)-In modern genetic usage, homeotic
mutations cause the development of tissue in an inappropriate
position; for example, bithorax mutations in Drosophila produce an
extra set of wings.
29) Bricolage-(tinkering) a term that rightly places the emphasis on modification of existing genes.
30) Homeodomain-
part of a transcription factor that binds to DNA, there
by regulating mRNA production.
31) Hox
gene family-homeobox gene in vertebrates, taking the gene
name from the first two letters of the orthologous gene in Drosophila
and adding an x. Show colinerarity, control organogenesis, are
homologous among Metazoans. Example of a hox gene mutation extra ribs.
32) Gene
regulation- has emerged as a central mechanism explaining
developmental and evolutionary change.
33) Paralogous genes (paralogues)-two or more different loci in the same organism that are
sufficiently similar in their nucleotide sequences (or in the amino acid sequences of their protein
products) to indicate they originated from one or more duplications of a common ancestral gene.
34) Orthologous genes (orthologues)- gene loci in different species that are sufficiently similar in
their nucleotide sequences (or amino acid sequences of their protein products) to suggest they
originated from a common ancestral gene.
35) Gene
family- two or more gene loci in an organism whose similarities
in nucleotide sequences indicate they have been derived by
duplication from a common ancestral gene.
36) Ostracoderms-
the earliest vertebrates (shell-skinned) are groups of
extinct, primitive, jawless fishes that were covered in an armor of
plates of true bone tissue. Small, slow swimming, bottom-dwellers.
Likely the first animals to use their gills for respiration.
37) Orthogenesis-
progressive pattern of improvement of a species
without much branching (example: the teeth of horses)
38) cleidoic
egg- the type of egg laid by reptiles and birds; it allows them
to reproduce out of and away from water by providing a moist
environment for the embryo
Chapter 12 People
By Nickolaus Willis & Zachary Meyer
 Ernst Mayr - One of the most influential evolutionary biologists of
the twentieth century, was a staunch defender of The Modern
Synthesis, a synthesis that he played a role in creating. His last book,
“What Evolution Is”, published 2001, is a thorough and thoughtful
exploration of Evolutionary Biology
 Francois Jacob and Jacques Monod (1910-1976) - In 1961 on the
genes governing the production of enzymes involved in lactose sugar
metabolism in the bacterium E. coli. This is the first study leading to
the discovery of gene regulation. For this fundamental discovery,
they received the 1965 Nobel Prize in Physiology and Medicine.

Andre Lwoff (1902-1994) - The director of the Pasteur Institute where Jacob and Monod
conducted their experiments, received the 1965 Nobel alongside of Jacob and Monod.

Andrew Fire and Craig Mello - Winners of the 2006 Nobel Prize in Physiology and Medicine for
their research on RNAi in animals.
 Barbara McClintock (1902-1992) - In the 1940’s and 1950’s she
discovered both Transposons and Gene Regulation. Her work was
ignored and misunderstood for decades until in 1983 she won the
Nobel Prize in Physiology and Medicine for her discovery of Genetic
Transposition.
 Edward B. Lewis - The American geneticist and founder of
developmental genetics studied the bithorax and related mutants in
Drosophila and their controlling homeotic genes in DNA in the
1970s through 1990’s. This led to the new subdiscipline ”Evo-Devo”
[evolutionary development]. He laid the groundwork for our current
understanding of the universal, evolutionarily conserved strategies
controlling animal development.
Chapter 12 Terms & Concepts
Lyddia Wilson & Zachary Meyer
 Regulatory mutation: changes that generally affect genes controlling
genetic pathways or networks
 Natural selection acts on existing phenotypic variation
 Mutations are necessary for evolution
o Spontaneous mutations
o Induced mutations
o Somatic mutations
o Germline mutations
 Point mutations occur through substitutions, insertions, deletions,
transposition
 Point mutations can be silent (more likely when it occurs in the third
position of the codon triplet), replacement, or stop codon
o Sickle Cell is an example of a point mutation; it results from a
mutated allele of the hemoglobin beta chain.
 A mutation will only be passed to offspring if the mutation occurs in
the germ cells leading to gamete production
 Somatic mutation: mutation acquired in any other cell – will not be a
heritable mutation
 Most chance mutations are likely to disrupt and not improve protein
function if there is any effect at all
 Sense mutation: change in DNA base, no change in amino acids
 Missense mutation: change in DNA base and change in amino acid,
but protein still functional
 Nonsense mutation: change in DNA base and change in amino acid,
and the protein is non-functional, a fragment, or not produced at all
 Pleiotropic effects – multiple effects
o A mutation can have a wide variety of effects if the individuals
with the mutant allele are exposed to a wide variety of
environmental conditions or selection pressures.
 Transposons or “jumping genes” direct the synthesis of additional
copies of themselves in the host genome
 Transposons may cause frameshift or other mutations.
 Chromosome number variation
o Entire sets of chromosomes
o Single chromosomes within a set
 Polyploidy = repetitive doubling
o More than 2 homologous sets of chromosomes
o Commonly found in plants
o May occur due to abnormal cell division with nondisjunction
o Especially common among ferns and flowering plants
 Plants may become tetraploid due to self-fertilization as well as less
commonly in animals by parthenogenesis (reproduction by females
without fertilization by males
 Plants may be able to survive better being polyploidy than animals
because they can tolerate extremely divergent structural relationships,
unlike animals
 Changes in the appearance (phenotype) of a chromosome (usually
observed in karyotype analysis):




o Deletions & deficiencies: remove chromosomal material
o Duplications: improperly repaired chromosome breakage
moves genes (DNA fragments) from one homologous
chromosome (which now has a deletion) to the other
homologous chromosome (which now has a duplication). Gene
duplications are the source of most new genes (loci) as well as
the development of families of related genes, such as the globin
chain families.
o Inversions: reversals in chromosome gene order
o Translocation: improperly repaired chromosome breakage
moves genes from one homologous chromosome to another
nonhomologous chromosome, the resulting hybrid segregating
together at meiosis; balanced translocations (in which there is
no net loss or gain of chromosome material) are usually not
associated with phenotypic abnormalities, although gene
disruptions at the breakpoints of the translocation can, in some
cases, cause adverse effects, including some known genetic
disorders; unbalanced translocations (in which there is loss or
gain of chromosome material) nearly always yield an abnormal
phenotype. In the simplest cases of translocation, a single locus
would move; in the largest case, an entire chromosome might
be added to a nonhomolog.
Inversion loops protect linked alleles from being separated by
crossing over
o Alleles in the inverted region are protected and passed as unit to
future generations
microRNAs (miRNA) regulate translation of mRNA into protein in
plants and animals
When a diploid gamete fertilizes a normal haploid gamete a triploid
individual is produced. These sets of 3 like chromosomes have
difficulty in the close alignment of synapsis
Equal crossing over provides new arrangements of alleles but has little
potential for new variation
 Unequal crossing over causes duplications on one chromosome and
deletions on the other. The duplications allow for new possibilities
for gene function in eukaryotic evolution.
 Mutations are expressed in gene activity:
o Changes within a gene product
o Changes in the regulation of a gene or its product
o May affect rate at which a gene is produced or whether or not
the protein is produced
 Phenotypic variation: anatomy, biochemistry, physiology, behavior,
etc.
 Genotypic variation: alleles, loci, chromosomes, genomes
 Mutation events increase genetic variation in populations and give
natural selection material from which to generate adaptive
evolutionary changes
 Most mutational processes are harmful and lead to decreased
adaptation most of the time
o But individuals being so numerous and given many millions
and billions of years to work with, beneficial changes do occur
 3 Major regulatory mechanisms control transcription of DNA
o ciso transo RNAi-regulation
 Minor mechanisms:
o Transposons
o Posttranscriptional modification
 Cis-Regulation elements
o Elements reside upstream from promoter region on same
chromosome
o Transcription factors – bind to cis-regulatory elements to
encourage or discourage transcription
 Trans-regulation
o DNA sequences that encode transcription factors
o Reside on other DNA molecule than the regulated gene
o TF’s can bind to cis-reg. elements or CAAT and TATA boxes
adjacent to a structural gene.
 Posttranscriptional modifications of eukaryotic nuclear (not organelle)
mRNA
o Introns must be removed from the transcribed pre-mRNA base
sequence and there can be options as to which introns are
removed and which exons are spliced to form the functional
mRNA
o Addition of the 5' (7-methylguanylate nucleotide) cap reduces
degradation of the capped mRNA by 5' exonucleases; facilitates
exit to the cytoplasm through the nuclear pore and assists in
orienting the capped end of the mRNA to the ribosome to
initiate translation
o Addition of poly-A tails of various lengths affects the lifespan
of the mRNA in the cytoplasm before it is degraded and
therefore, how many polypeptide chains can be translated from
one mRNA
o Other modifiers (proteins and regulatory RNAs) can bind to the
mRNA to delay or prevent translation.
 Small interfering RNA (siRNA), sometimes known as short
interfering RNA or silencing RNA, is a class of double-stranded RNA
molecules, 20-25 base pairs in length. siRNA plays many roles, but it
is most notable in the RNA interference (RNAi) pathway, where it
interferes with the expression of specific genes with complementary
nucleotide sequences. siRNA functions by causing mRNA to be
broken down after transcription,[1] resulting in no translation. siRNA
also acts in RNAi-related pathways, e.g., as an antiviral mechanism or
in shaping the chromatin structure of a genome.
 microRNA (miRNA) - small non-coding RNA molecules
(containing about 22 nucleotides) found in plants, animals, and some
viruses, which functions in RNA silencing and post-transcriptional
regulation of gene expression. Encoded by eukaryotic nuclear DNA
in plants and animals and by viral DNA in certain DNA viruses,
miRNAs function via base-pairing with complementary sequences
within messenger mRNA molecules. As a result, these mRNA
molecules are silenced by one or more of the following processes: 1)
cleavage of the mRNA strand into two pieces, 2) destabilization of the
mRNA through shortening of its poly(A) tail, and 3) less efficient
translation of the mRNA into proteins by ribosomes. miRNAs
resemble the small interfering RNAs (siRNAs) of the RNA
interference (RNAi) pathway, except miRNAs derive from regions of
RNA transcripts that fold back on themselves to form short hairpins,
whereas siRNAs derive from longer regions of double-stranded RNA.
The human genome may encode over 1000 miRNAs, which are
abundant in many mammalian cell types and appear to target about
60% of the genes of humans and other mammals. miRNAs are well
conserved in both plants and animals, and are thought to be a vital and
evolutionarily ancient component of genetic regulation though they
appear to have evolved independently from the ancestral state in the
two kingdoms and to have different modes of action. miRNAs can be
carried by vectors from one cell to another and so may participate in
HGT.
 Transposable elements:
o Think of them as molecular parasites which may accidentally
create adaptive (or harmful) mutations and phenotypic
variations
o Transposons: produce special transposase enzymes that allow
it to insert copies of itself into various target sites in an
organism’s nuclear
Chapter 13 People
Maranda Stokes & Kathryn White
Bernard Kettlewell- field studies in Britain in the 1950s tested
the hypothesis that bird predators were altering the frequencies
of the color morphs based on the moths’ contrast to their
backgrounds (tree bark) when they were at rest.
Experiments: studies demonstrated that native birds did
eat peppered moths. Release and capture studies in two areas
indicated that peppered forms survived in greater numbers in
unpolluted forests while melanic forms survived in greater
numbers in soot polluted forests. In his famous experiment, he
placed moths on dark and pale tree trunks and showed that
background strongly influenced moth survival against predation.
His career’s work was summarized in The Evolution of
Melanism: a study of recurring necessity; with special reference to
industrial melanism in the Lepidoptera (1973).
Pietrewicz and Kamil (1977) tested if choices by moths were selectively advantageous.
Experiment: Trained blue jays to respond to slides of moths by pecking a button for
a food reward whenever they spotted a moth. Results showed that blue jays spotted moths
less often on birch trees and especially when moth was oriented with its head up
Judith Hooper was a British journalist who wrote Of Moths and Men. The book attacked
Kettlewell . It has been dismissed by scientists for lack of scientific understanding, prejudice
and careless journalism.
Godfrey H. Hardy (English mathematician 1877-1947), Wilhelm
Weinberg (German physician 1863-1937), W.E. Castle
(American geneticist) each independently concluded that the
original proportions of the genotypes in a population remain
constant from generation to generation as long as the five H-W
assumptions are met:
p2 + 2pq + q2 = 1 (the Hardy-Weinberg Equation)
p2 = individuals homozygous for first allele
2pq = individuals heterozygous for the alleles
q2 = individuals homozygous for second allele
R. A. Fisher (one of the founders of population genetics) noted that
the greater the genetic variation upon which selection for fitness may
act, the greater the expected improvement in fitness.
Sewall Wright (1889-1988) proposed that genetic drift can be quite
important in changing allele frequencies among populations when the
effective size of the population is small. His proposal is known as the
shifting balance theory.
Peter R. and B. Rosemary Grant concluded from their long-term
study of selective changes in Darwin’s finches on the Galapagos
Islands, “The population tracks a moving peak in an adaptive
landscape under environmental fluctuations, and there is more than
one individual fitness optimum within the range of phenotypes in the
population.
Sewall Wright, R.A. Fisher J.B.S. Haldane-acknowledged founders
of the neo-darwinian theory of evolution based on population
genetics.
Chapter 13 Terms & Concepts
CJ Parchman & Kathryn White
Key Concepts
 Without variation there would be no evolutionary change
 Mutation provides one source of genetic variation
 Mutation is not entirely random: some parts of the genome are
more susceptible to mutation than are others
 The large amount of polymorphism at gene loci provides a
much greater source of genetic variation than do the relatively
few new mutations that arise each generation.
 At the population level, allele frequency provides a measure of
genetic variations
 Genetic drift within a population and gene flow between
populations provide sources of genetic variation
 Genetic variation provides the row material enabling
evolutionary change in response to natural selection
 Large-scale geographical patterns of species distribution can be
determined using the genetic history of populations
Mutation - any change in the cell’s DNA base sequences
Mutation rate – the probability that a gene will mutate when the cell
divides
Contributions to enhanced variation at the population level:
- Mutation
- Random drift in gene frequencies within a population
- Gene flow between populations
Quantitative trait loci (QTL) - regions of that contain blocks of genes,
often influencing characters that show continuous variation, such as height
or weight
Contributions to the maintenance of genetic diversity (genetic
polymorphism) within populations:
-randomness of mutation
-variation in mutation rates among genes and among species
-frequency of alleles in populations
-ability of DNA to repair itself
Mutations supply an important source of variation upon which selection acts
and which selection incorporates into evolutionary change.
Optimal mutation rates are advantageous.
Hot Spots of Mutation - specific nucleotide sequences that are the sites
where the nucleotide change is less readily repaired or compensated for than
is a sequence change at another site
Mutation rates are not only low, they are not constant. As with other
essential traits, mutation rates seem mostly selected for optimum values,
balancing on the delicate adaptive line between retaining prevailing adaptive
features yet facilitating the origin of new features.
A remarkable way in which some organisms accumulate mutations without
experiencing immediate effects is to bind their gene products with heat
shock proteins.
Heat shock proteins (hsp) - molecular chaperones that help other proteins
maintain their normal 3D conformation and prevent them from degrading.
• Heat shock proteins may be disabled in new stressful environments
– dramatic change in temperature
– dramatic change in pH
– dramatic change in salinity
Evolutionary potential and genetic variation are two sides of the same
evolutionary coin.
Genetic polymorphism - The presence of two or more alleles, each at a
frequency of 1% or more, at a gene locus in the gene pool of a deme or of an
entire species over a succession of generations. Genetic polymorphism
provides a much greater source of genetic variation with the potential for
evolutionary change than do the relatively few new mutations that arise in
each generation.
Genetic polymorphism is called balanced polymorphism when the
persistence of the different alleles cannot be accounted for by mutation
alone. In such cases, selection and/or migration are often the cause.
Researchers may focus on obvious phenotypic changes such as Mendel
observed, called discontinuous variation, evidenced in characters that form
a few distinct phenotypic classes, e.g., red, pink, or white flower color; or on
small changes or continuous variation, evidenced in characters for which
the plots of the distribution of the variation form a bell-shaped curve or
normal distribution, e.g., height or body mass of most animals or plants.
Enzyme polymorphism-Change in catalytic ability due to change in
temperature, osmotic environment, pH,
DNA sequence polymorphism-Changes in bases, codons, introns, exons,
etc.
Polygenic inheritance, also known as quantitative or multifactorial
inheritance refers to inheritance of a phenotypic characteristic (trait) that is
attributable to two or more genes, or the interaction with the environment, or
both; do not follow patterns of Mendelian inheritance (separated traits).
Instead, their phenotypes typically vary along a continuous gradient depicted
by a bell curve
Population- group of individuals of the same species that can interbreed
with one another
Polymorphism – many traits display variation within a population
– Due to 2 or more alleles that influence phenotype
Polymorphic gene- 2 or more alleles
Monomorphic – predominantly single allele
Single nucleotide polymorphism (SNPs)
– Smallest type of genetic change in a gene
– Most common – 90% of variation in human gene sequences
Balanced polymorphism- the persistence of two or more different genetic
forms through selection
Quantitative trait loci (QTL) – all of the genes (alleles) in a particular
region of a chromosome that affect a quantitative aspect of the phenotype
QTL analysis enables us to isolate suites of genes acting on particular parts
of the phenotype at particular stages in ontogeny and to determine their
relative affects.
In the 1930’s, it became accepted that:
1.) Evolution is a population phenomenon that
2.) can be represented as a change in gene (now allele) frequencies
because of the action of various natural forces such as mutation,
selection and genetic drift, and that
3.) these changes can lead to differences among populations, species, and
higher clades. This population genetics view of evolution became
known as the neo-Darwinian theory with its emphasis on the
frequency of genes in populations as the basis of evolutionary change.
Population genetics deals with genes as alleles and gene frequencies as
allele frequencies.
Allele frequencies (the frequencies of individual alleles) and the gene pool
(all the alleles of all individuals in the population) are two major attributes
of a population.
Hardy-Weinberg principle –The conservation of gene (allelic) and
genotype frequencies in large populations under conditions of random
mating and in the absence of evolutionary forces, such as selection,
migration, and genetic drift, which act to change gene frequencies.
1) diploid organisms
2) sexual reproduction
3) generations are non-overlapping
4) equally viable genotypes
The Hardy-Weinberg principle is the founding theorem of population
genetics.
Population – a group of sexually interbreeding or potentially interbreeding
individuals
Nonrandom Mating- mating between specific genotypes shifts genotype
frequencies
– Assortative Mating: does not change frequency of individual
alleles; increases the proportion of homozygous individuals
– Disassortative Mating: phenotypically different individuals
mate; produce excess of heterozygotes
Deme – local population of organisms of one species that interbreed with
one another more than they do with other demes and share a distinct gene
pool. The considerable genetic variability in human groups shows that
populations of modern humans are demes.
Genetic load - the extent to which a population departs from an optimal
genetic constitution; the loss in average fitness of individuals in a
population because the population carries deleterious alleles or
genotypes.
Genetic death - can be classified as either sterility, inability to find a mate,
or by any means that reduces reproductive ability
A population may receive alleles from a nearby population in a process
known as gene flow or sometimes as migration because individuals,
gametes, or even individual genes, move from population to population,
taking their alleles with them.
At least three factors have an impact on the recipient population:
1. the difference in gene frequencies between the two populations
2. the proportion of migrating genes incorporated into each
generation; and
3. the pattern of gene flow, whether occurring once or continually
over time.
4. Gene flow-a movement of genes from one population to another
Gene flow-a movement of genes from one population to another
Genetic drift – a consequence of random fluctuations in gene frequencies
that arise in small populations; in large populations, it is countered by
selection
Effective population size (Ne) – formula for calculating the number of
parents who actually contribute offspring to the next generation.
(Ne) = (4NfNm/(Nf+Nm) where Nf in the number of female parents and Nm is the number
of male parents. Ne is the number of parents who actually contribute offspring to the next
generation.
We can conclude that genetic drift increases with variation between
populations, but on the average, not in any particular direction.
R.A. Fisher formulated a fundamental theorem that essentially states that the
greater the genetic variation upon which selection for fitness may act, the
greater the expected improvement in fitness.
Variation itself is subject to selection, and so the propensity to vary
(variability) is an important attribute of organisms.
Phylogeography – The study of the evolutionary processes regulating the
geographic distributions of lineages/groups by reconstructing genealogies of
individual genes, groups of genes or populations.
The neo-Darwinian theory
1. Evolution is a population phenomenon
2. Evolution when there is a change in gene (now allele) frequencies
in a population because of various natural forces such as mutation,
selection and genetic drift
3. These changes in allele frequencies lead to differences among
populations, species, and higher clades
4. This population genetics view of evolution became known as neoDarwinian theory with its emphasis on the frequency of genes in
populations
Five agents of Evolutionary Change:
1. Gene Flow
2. Selection
3. Nonrandom mating
4. Genetic drift
5. Mutation
Founder Effect - A situation encouraging genetic drift that occurs when a
few individuals (founders) derived from a large population begin a new
colony. Since these founders carry only a small fraction of the parental
population’s genetic variability, different gene frequencies can become
established in the new colony.
Bottleneck Effect – A situation encouraging genetic drift that occurs when a
population is reduced in size and later expands in numbers. Since the
survivers carry only a small fraction of the parental population’s genetic
variability, different gene frequencies can become established in the
surviving population.
Shifting Balance Theory- proposed by Sewall Wright in 1931
1. Genetic drift, acting on genetic variation at various loci, allows a
number of demes to change their allele frequencies. As fitness
changes such demes are modeled as moving across non-adaptive
valleys to different parts of an adaptive landscape, a model
discussed in Chapter 15.
2. Selection pushes some of these demes up the nearest available
adaptive peak by changing allele frequencies even further.
3. Variation at other loci provides further opportunity for genetic drift
to move a population to a higher adaptive peak.
4. A deme that has a high fitness coefficient tends to displace other
demes of lower fitness by expanding in size or dispersing outward
and changing the genetic structure of other demes through
migration.
5. Environmental change such as a stream of seismic earthquakes,
can act on populations by changing the environment to which
populations must adjust or perish. Channeling selection in new
directions encourages populations to continually shift their genetic
structures. “The population tracks a moving peak in an adaptive
landscape under environmental fluctuations and there is more than
one individual fitness optimum within the range of phenotypes in
the population.” –P.R. and V.R. Grant
6. Selection, time, and genetic accident are needed to achieve the
most optimum genotypes, although genetic loads and changes in
the environment can oppose achieving the optimal genotype.
Red Queen Hypothesis - the hypothesis that adaptive evolution in one
species of a community causes a deterioration of the environment of other
species. As a consequence, each species must evolve as fast as it can in order
to continue to survive. It comes from Lewis Carroll's Through the Looking
Glass in which the Red Queen said to Alice, “Now, here, you see, it takes all
the running you can do, to keep in the same place.”
Chapter 14 People
David Hansen & Trent Gaasch
Thomas Austin in 1759 introduced 24 wild rabbits Oryctolagus cuniculus for sport hunting in
Austrailia that spread out of control.
Robert H. MacArthur (1930-1972):
 One of America’s major 20th century ecologists.
 A leader in moving ecology from a descriptive to an experimental
discipline.
 He did research on niches and foraging behaviors.
 The Robert H. MacArthur Award is awarded for meritorious
contributions to ecology.
Edward O. Wilson (1929-Current ):
 One of America’s major 20th century evolutionary biologists.
 A specialist in social insects who became a major theorist and
later a major advocate for understanding and protecting
biodiversity.
 Founder of a subdiscipline: Sociobiology: The New Synthesis
(1975).
Richard Lewontin:
• American evolutionary biologist.
• Captured the essence of the niche and of the evolutionary
relationships of an organism to its (self-made) environment in his
2000 book, “The Triple Helix: Gene, Organism, and Environment.”
Chapter 14 Concepts and Vocabulary
Emily Towery & Trent Gaasch
Co-evolution is the set of mutual evolutionary influences shared
between two or more species occupying a common habitat; possible
when there is some overlap among the niches of two or more species;
when two (or more) species: (1) exert selective pressures on each other,
and (2) evolve in response to each other
Because each species is evolving in response to the other, one important
feature of co-evolution is that the:
• Selective environment is constantly changing
• Also, selective pressures will be strongest when there is a close
ecological relationship
• Species do not evolve in a vacuum
• Darwin emphasized competition between members of the same
species for limited resources
• Ecologists emphasize the competition between different species
for the same limited resources
• Co-evolution includes competition for both abiotic and biotic
resources
Co-Evolution with Pathogens:
Thomas Austin’s rabbits population boom; introduction of
myxomavirus; mortality rates in rabbits about 90%; now rabbit
population is smaller but virus only has about 40% mortality rate
because of surviving resistant rabbits and evolution of less virulent
pathogen
Definitions of Niche

Where an organism is found and what it does there
• The role of an organism in an ecosystem
• The role of a species within a community
• All the functional roles of an organism in a biological community
• A unique ecological role of an organism in a community
• The environmental habitat of a population or species, the
resources it uses and its interactions with other organisms
• The status of an organism within its environment and community
as it affects the survival of the species
• The role or functional position of a species within the community
of an ecosystem
• The physical and functional role of an organism within an
ecosystem
Competition arises when two groups depend on the same limited
environmental resources so that each group causes a reduction in the
other’s numbers, often with important ecological or behavioral
consequences.
• Three consequences of competition are outlined below:
o Resource partitioning
 The situation in which competing groups of
organisms minimize the harmful effects of
direct competition by using different aspects of
their common environmental resources
o Character displacement:
 Phenotypic differences accompany resource
partitioning among coexisting groups
o Competition Exclusion
 The principle that two species cannot continue
to coexist in the same environment (niche) if
they use it in the same way.
Important ecological relationships that give rise to coevolution:
1. Predator and Prey – predators can reduce the possibility of a
dominant species reaching its carrying capacity; prey species
crash first, then predators starve
Defenses against Predators:
 Camouflage
 Startle Responses - When a prey species can change its
appearance suddenly and therefore frighten or distract a
predator; example include wing or body displays that reveal
eyespots, or other color changes from behavior that confuse
the predator, such as flicker fusion when a striped snake
starts moving and the stripes become a blur.
 Flash Coloration - a patch of bright contrasting color that is
revealed, e.g., by unfolding wings, apparent only during
motion on an otherwise neutrally tinted animal and that is
believed to distract the attention of predators who lose
sight of the prey when it comes to rest and the flash color
patch is obscured
 Aposematic Behaviors
 Aposematic Colors
 Toxicity
 Mimicry
 Ingestion Defenses: Spikes & Horns & Thorns - a tough,
sharp, protective defensive external surface projection to
reduce the desire of biting organisms to bite into the target
organism's tissues; it includes spikes, horns, thorns, spines,
etc. (They may serve other adaptive purposes as well.)
 Ingestion Defenses: Fangs & Tusks - sharp teeth which
may be used to discourage predators from biting a target
organism. (They may serve other adaptive purposes as
well.)
 Ingestion Defenses : Armor - a tough, protective defensive
external covering to reduce the penetration of biting
organisms into the target organism's tissues; it includes cell
wall material, shells, exoskeletons, dermal thickenings,
bones and bony plates, etc.
 Ingestion Defenses: Toxic Chemicals
2. Parasite and Host
3. Mutualists
4. Competitors(as described above)
 Resource Partitioning
 Character Displacement
 Competitive Exclusion
Detritivores – eukaryotes (certain protistans and animals) which use
for the mechanical breakdown (chewing) to feed on dead organic
material (detritus)
Decomposers – prokaryotes (certain bacteria) and eukaryotes (certain
protistans and fungi) which use externally secreted enzymes for the
chemical breakdown (chemical digestion) to feed on dead organic
material (detritus)
bone morphogenic protein 4 (Bmp-4) – a homeobox (hox) gene; its expression is a major
contributor to jaw size and tooth development in fish as well as beaks in birds; controls dorsi-ventral
differentiation of mesodermal tissues in other animals
Change in expression of a single gene explains why significant
morphological change can occur in just a few generations, as
observed in the Darwin’s finches.
phenotypic plasticity - facultative ability of a single genotype to
produce more than one phenotype:
• The variation in phenotype (for a given genotype) which
occurs due to the influence of environmental factors.
• Can represent the small and sometimes trivial differences
which we observe in identical twins (perhaps a taller, more
muscular twin works out more or has better diet than other
twin).
• Represents the sorts of regular changes observed when
individuals of the same genotype develop or behave
differently when they live in different environments
• One phenotype may be a negative consequence of an
inadequate environment.
• Phenotypic plasticity can evolve like any other potentially
adaptive trait
Examples of Phenotypic Plasticity
• Interactions between individuals of predator and prey species of
rotifers (Phylum Rotifera); when the predator is present, the prey
species detects predator chemicals and grows defensive spines
• Daphnia species respond to predators; individual water fleas have
the potential to grow a “helmet” and longer spine when exposed
to chemicals from various of their natural predators (midge larvae
and fish); the genetic potential was already present in the Daphnia
genome, but it requires the action of the predator’s chemical cues
to activate the genes for the altered morphology
• In spadefoot toads: when crowded, large cannibalistic morphs
develop which prey on the normal tadpoles
• Moth Nemoria arizonaria: something in the oak plant tissue
consumed by the caterpillar drives the change in morphology
(spring caterpillar morph resembles blossom of tree, summer
morph resembles twig on tree)
Life history strategies occur along a continuum characterized as r- and
K-selection
• Where individual species fall on the r-K continuum is largely
determined by the environment in which they live and the
environment they live in is influenced by their presence and life
styles
• McArthur & Wilson developed an elegant system for describing
the stability and age distribution of natural populations known as
“r/K selection”
The variables r and k in r-and k-selection come from the logistic
equation for population growth

I = rN (K-N / K) calculates the annual growth of a population
 I = the annual increase for the population,
 r = the annual growth rate: (birth rate + immigration rate) –
(death rate + emigration rate)
 N = the population size
 K = the carrying capacity: (max density at which population
can exist in given environment)

Habitat
Succession
Stage
Population
Growth
Potential vs.
Extinction
Potential
Competition
Among
Individuals
Life History
Traits and
Mortality
r-Strategist
unstable, variable,
ephemeral, unpredictable
early “weedy” colonists,
good dispersal abilities
maximized, exponential;
less vulnerable to extinction
K- Strategist
long term stability
variable, reduced;
resources exceed demand;
weak competitors
precocial young, early
maturity onset, shorter
generation time; mortality
high, variable and
unpredictable
continual and intense,
resources in short supply;
good competitors
altricial young, late maturity
onset, longer generation
time; mortality low, more
constant and predictable
climax community, reduced
dispersal abilities
low, at equilibrium;
vulnerable to extinction
Body Size
small
Fecundity
high
and
Dispersal
Rates
Resource
high but individual
Allocation to offspring are of low quality;
Reproduction reduced parental care
Life Strategy
many offspring, few
Trade Off
survive to reproduce
larger
low
low but individual offspring
are of high quality;
increased parental care
few offspring, most survive
to reproduce
Climax community – stable community; likely to persist for long
periods of time
The Red Queen Hypothesis - the hypothesis that adaptive evolution in one
species of a community causes a deterioration of the environment of other
species. As a consequence, each species must evolve as fast as it can in order
to continue to survive. It comes from Lewis Carroll's Through the Looking
Glass in which the Red Queen said to Alice, “Now, here, you see, it takes all
the running you can do, to keep in the same place.” The Red Queen
Hypothesis is used to describe two similar ideas based on co-evolution
relationships or evolutionary arms races; one relating to extinction
probability, the other to the value of sexual reproduction.
• The original idea, proposed by Leigh Van Valen in 1973, is that coevolution could lead to situations for which the probability of
extinction is relatively constant over millions of years rather than
being proportional to the population's lifetime. In tightly coevolved interactions, e.g., predator and prey, or host and parasite,
the sudden evolutionary change by one species could lead to the
extinction of other species and that the probability of such
changes might be reasonably independent of species age. This is
the long term paleontological macroevolutionary perspective.
• The other idea, advocated by W.D. Hamilton, among others,
relates to the benefit of sexual reproduction. This idea is that coevolution, particularly in evolutionary arms races between hosts
and parasites, could lead to sustained oscillations in genotype
frequencies. As one genotype of host is most susceptible, its most
effective parasitic genotype will prosper. However, this forms a
selection pressure to favor a resistant host. When that resistant
host genotype appears or merely increases in numbers, a new
selection pressure forms on the original parasite genotype, which
is now less infectious or virulent in the new host genotype. Thus,
one host genotype will replace a former one, only to be followed
by parallel replacement of genotype in the parasite. Sexually
reproducing species which allow recombination of alleles among
different individuals in their populations will have the potential
for more rapid evolutionary change, speeding up the oscillations
in genotypes of hosts and parasites, even if no new alleles arise in
either gene pool. This hypothesis can also explain the shift
between sexual and asexual modes of reproduction in species
capable of both forms of reproduction. This is the short term
neontological (living species) microevolutionary perspective.