Unit 1, EVOLUTION chapters 16 – 19
The lines between chapters will be blurred as we attempt to
interconnect all information.
Chapter 16
– Changing Theories.
– Continental Drift.
– Fossil Evidence.
– Change Agents (scientists and contributions)
– CHANGING THEORIES
Throughout the 1800s and early 1900s, scientists were making
huge discoveries traveling in collecting data from all over the
world. They were building on information of past scientists,
interviews were changing.
– CONTINENTAL DRIFT
– At least 5 times in Earth’s history, super continents have
formed.
– Gondwana and Pangaea are 2 of the most famous
–Continental drift theory actually supports uniformitarianism
proposed by Charles Lyell as it is a slow continual process.
– Plate boundaries
http://www.bethel.k12.oh.us/gatrellm/environmental-science/
– FOSSIL EVIDENCE
– How do fossils form?
Fossils form when recently deceased organisms are buried
by sediment or ash creating an anaerobic environment.
Mineral rich groundwater seeps into the remains where metal
ions and other inorganic compounds gradually replace minerals
in bones or other hard tissues.
– What are the chances of becoming a fossil?
– Fossil record
– geologic time is significantly marked by a line they called
the KT boundary. This stands for Cretaceous tertiary
boundary, and marks the end of the reign of dinosaurs, and
one of our largest mass extinctions.
– Radiometric dating.
– Radiometric dating is a form of calculating the age of
a substance based upon the average decay of radioactive
isotope.
– Radiometric dating often uses carbon-14, which is a
natural radioactive isotope found in living tissues. The ratio of
carbon 12 carbon-14 is used to calculate how long ago it
organism lived. The half-life of carbon-14, is 5370 years.
– The stability of the original atoms may play a factor in
the accuracy of these tests.
http://www.scientificamerican.com/article/carbon-datinggets-reset/
– CHANGE AGENTS:
– George Cuvier proposed in the early 1800s
catastrophism, sudden abrupt changes shape the face
of the earth [wrong]
– Jean Baptiste Lamark proposed acquired traits,
improvements and organism gained over the lifetime
were passed to offspring. [Wrong]
– Charles Darwin proposed evolution through the process
of natural selection, organisms with favorable traits
outperform and out reproduce organisms with less
favorable traits. Causing change over time in organisms
more fit to their environment. 1831 same time as our
civil war.
– Charles Lyell proposed the theory of uniformity, study
ongoing geologic change. Darwin read his book during
his journey.
– Alfred Wallace proposed the theory of natural
selection. While working in the Amazon, at the same
time as Darwin. He is known as the father of
biogeography. Emphasizing how animals traits are fit to
their specific geographic conditions.
Chapter 17
– Natural Selection.
– Genetic Equilibrium.
– Microevolution.
– Speciation.
– Macro evolution.
NATURAL SELECTION-
– Natural selection is a process which allows certain
individuals with favorable traits more fit to their
environment to be stronger, healthier and have higher
reproductive capabilities than other organisms within their
species. This is generally due to a favorable genotype for a
specific trait which will be passed to future generations.
– Populations evolve through natural selection, not individuals.
– Differences in allele combinations (genotype) result in
phenotypic variations. Some of which are better suited to
their geographic conditions and give them a better chance
of survival.
– Mutations within in allele may account for these variations.
Remember, not all mutations are negative. Some, though
random, may provide benefits.
– Several patterns of natural selection exist:
o directional selection – individuals with a trait that is at
one extreme of a variation is selected against
 an example is antibiotic resistant bacteria or rats
that cannot be killed with warfarine
o stabilizing selection – the midrange of a genetic
variation are favored.
 Example sociable weavers of the African savanna
favor a midrange body weight bigger birds starve
more easily, tinier birds don’t store the fat to
survive
o Disruptive selection – forms at the extremes of the
range of variation are favored.
 Example African seed cracker birds feed on either
very hard sedge seeds or soft sedge seeds. Larger
billed birds feed on the harder seeds, while
smaller billed birds feed on softer seeds. Medium
billed birds do not open either as efficiently.
CREATING DIVERSITY-Sexual Dimorphism- differing appearances between the
sexes tends to lead to extravagant coloration, markings or
horns. These things set the males(usually) apart and often make
them targets for predation. So why are these phenotypes
passed on???
-Sexual selection- in which the “winner” of the mate gets
the opportunity to reproduce more frequently.
-Balanced Polymorphism- multiple alleles are maintained at
fairly high rate within a population. Often times more unique
phenotypes are the sexual preference so their alleles become
more frequent w/in the population. Then other phenotypes are
more rare and become the preference. This is called FrequencyDependent Selection.
-Genetic drift occurs when the allele frequency
RANDOMLY changes over time.
http://www.cengage.com/biology/book_content/9781111425692
_starr_udl13e/animations/PowerPoint_Lectures/chapter17/vid
eos_animations/computer_drift_v2.html
-Gene Flow occurs in populations which are more mobile.
They are free to move within other populations of the same
species.
LOSING DIVERSITY-Over time genetic diversity can be lost.
-Alleles that don’t vary are said to be Fixed.
-A Bottleneck is a large reduction in a population size due
to extreme selection pressure. (sometimes hunting) Small
populations tend to have many homozygous alleles.
-The Founder Effect occurs when a small group of
individuals establish a population.
-Inbreeding often occurs due to the founder effect, in
which allele variety is low.
 Ex: Ellis-van Creveld Syndrome in old order
Amish of Lancaster County characterized by
dwarfism, polydactyly, and heart defects.
MICROEVOLUTION –
– any change in allele frequency within the gene pool of a
population is considered microevolution.
SPECIATION-
– The process in which new species arise is speciation and it
can occur in a variety of ways.
o Isolation mechanisms prevent organisms from
reproducing and exchanging genetic material.
o Sympatric Speciation- occurs when populations
without physical barriers speciate.
http://www.cengage.com/biology/book_content/978111
1425692_starr_udl13e/animations/PowerPoint_Lectur
es/chapter17/videos_animations/wheat_speciation.htm
l
 Temporal Isolation- timing of reproduction differs
 Mechanical Isolation- reproductive parts do not
match up.
 Ecological Isolation- populations are adapted to
different microenvironments. High mountain plants
vs lower slope plants w/in a Mtn range
 Behavioral Isolation- they just don’t understand
each other (courtship rituals)
 Gamete Incompatibility- molecular incompatibility
prevents fusion of egg and sperm. No zygote can
arise.
 Hybrid Inviability- may end up with extra or not
enough chromosomes which can disrupt embryonic
development.
 Hybrid Sterility- some interspecies crosses will
produce healthy but sterile offspring. A mule’s 63
chromosomes cannot pair evenly during meiosis.
 Polyploidy- occurs due to chromosomes not
separating properly during meiosis causing
repeating genes (more alleles) This can cause rapid
speciation and in plants often creates hardy
varieties.
o Allopatric Speciation- occurs when a physical barrier
separates a population. Archipelagos are often a good
example. Hawaiian Honeycreepers
http://www.cengage.com/biology/book_content/978111
1425692_starr_udl13e/animations/PowerPoint_Lectur
es/chapter17/videos_animations/archipelago.html
o Parapatric Speciation- occurs when adjacent
populations speciate despite contact across a common
border. Often due to local selection.
GENETIC EQUILIBRIUM– Hardy Weinberg – Godfrey Hardy and Wilhelm Weinberg
derived a strange calculation about how populations remain
the same called genetic equilibrium.
– Since genetic equilibrium doesn’t usually exist. The
measurement between equilibrium and a real population will
prove evolution is occurring .
– Conditions for genetic equilibrium are as follows:
1. mutations don’t occur.
2. Population is infinitely large.
3. Population is located away from other populations
of the same species [no gene flow]
4. mating is random.
5. All individuals survive and produce the same
number of offspring.
To begin: all allele frequencies always add to 1.
For a gene with 2 alleles
Remember the basic formulas:
p2 + 2pq + q2 = 1
and
p + q = 1
p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals
REMEMBER: paired alleles assort independently during the
formation of gametes (Mendel) and meet up at fertilization in
predictable proportions.
Frequencies of the genotypes. What ever they may be, will
always add up to 1.
EXAMPLE: incomplete dominance,
dark blue flower color.
B (p)
b (q)
so BB= p2, Bb=2pq, bb=q2
Where p2+2pq+q2=1
Lets do some examples. Turn to page 274.
1. PROBLEM #1.
You have sampled a population in which you know that the percentage of the
homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:
A. The frequency of the "aa" genotype. Answer: 36%, as given in the problem itself.
B. The frequency of the "a" allele. Answer: The frequency of aa is 36%, which
means that q2 = 0.36, by definition. If q2 = 0.36, then q = 0.6, again by definition.
Since q equals the frequency of the a allele, then the frequency is 60%.
C. The frequency of the "A" allele. Answer: Since q = 0.6, and p + q = 1, then p =
0.4; the frequency of A is by definition equal to p, so the answer is 40%.
D. The frequencies of the genotypes "AA" and "Aa." Answer: The frequency of AA
is equal to p2, and the frequency of Aa is equal to 2pq. So, using the information
above, the frequency of AA is 16% (i.e. p2 is 0.4 x 0.4 = 0.16) and Aa is 48% (2pq
= 2 x 0.4 x 0.6 = 0.48).
E. The frequencies of the two possible phenotypes if "A" is completely dominant
over "a." Answers: Because "A" is totally dominate over "a", the dominant
phenotype will show if either the homozygous "AA" or heterozygous "Aa"
genotypes occur. The recessive phenotype is controlled by the homozygous aa
genotype. Therefore, the frequency of the dominant phenotype equals the sum of
the frequencies of AA and Aa, and the recessive phenotype is simply the
frequency of aa. Therefore, the dominant frequency is 64% and, in the first part
of this question above, you have already shown that the recessive frequency is
36%.
MINDY-COVER THE SCREEN
1. PROBLEM #2.
Sickle-cell anemia is an interesting genetic disease. Normal homozygous
individials (SS) have normal blood cells that are easily infected with the
malarial parasite. Thus, many of these individuals become very ill from
the parasite and many die. Individuals homozygous for the sickle-cell
trait (ss) have red blood cells that readily collapse when deoxygenated.
Although malaria cannot grow in these red blood cells, individuals often
die because of the genetic defect. However, individuals with the
heterozygous condition (Ss) have some sickling of red blood cells, but
generally not enough to cause mortality. In addition, malaria cannot
survive well within these "partially defective" red blood cells. Thus,
heterozygotes tend to survive better than either of the homozygous
conditions. If 9% of an African population is born with a severe form of
sickle-cell anemia (ss), what percentage of the population will be more
resistant to malaria because they are heterozygous (Ss) for the sicklecell gene?
ANSWER
Answer: 9% =.09 = ss = q2. To find q, simply take the square root of 0.09 to get 0.3.
Since p = 1 - 0.3, then p must equal 0.7. 2pq = 2 (0.7 x 0.3) = 0.42 = 42% of the
population are heterozygotes (carriers).
NEED MORE http://www.k-state.edu/parasitology/biology198/answers1.html
MACROEVOLUTION
•
large-scale evolution, patterns of change, such as one
species giving rise to many, the origin of major groups, and
major extinction events.
 Stasis – organisms persist for millions of years with little
or no change
 Exaptation – an adaptation of an existing structure for a
completely different use. example: feathers in birds
versus dinosaurs.
 Mass extinctions – huge extinction episodes eradicating
the majority of species on earth. Fossil records indicate
more than 20 mass extinctions have occurred.
 Adaptive radiation – a population rapidly diversified into
several new species. [Honey creepers]
 co-evolution – close ecological interest between 2 species
cause them to evolve jointly. One species act as a
selective agent on the other species.
Chapter 18
-Phylogeny
-Morphology
-Mutations
-Patterns of Embryonic Development
PHYLOGENY phylogeny is the evolutionary history species, or group, it’s
kind of like a genealogy family tree.
 A Character is A measurable inherited trait, shared
characters insinuate a common ancestor.
 A Clade is a group’s members share one or more derived
traits, traits that is present in a group, but not ancestors,
many clades are equivalent to taxonomic groups.
 Example: flowering plants are both a clade and a
phylum.
 Monophyletic groups – consists of an ancestor, together
with all of its descendents.
 Cladistics – making hypotheses about evolutionary
relationships among clades. The process of finding the
simplest pathway is called parsimony analysis. Cladogram
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
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are type of evolutionary tree that summarizes our best
data supported hypotheses about how a group of clades
evolved.
Cladistic’s analyses are also used to correlate past
evolutionary divergences with behavior and dispersal
patterns of existing population, patchy distribution of
preferred food plans may prevent gene flow and lead to
catastrophic loss of genetic diversity in populations under
pressure.
http://www.cengage.com/biology/book_content/978111142
5692_starr_udl13e/animations/PowerPoint_Lectures/chapt
er18/videos_animations/cladogram_interpretation.html
Evolutionary relationships are often determined by the
accumulation of neutral mutations within populations. The
molecular clock based upon accumulating mutations may help
scientists calculate how long ago organisms share a common
ancestor.
Evolutionary biologists compare protein sequences among
several species and use the number of differences as a
measure of relative relatedness. [Interesting]
medical researchers use phylogeny to study the evolution
of viruses such as H1N1.
MORPHOLOGY
 morphology refers to the appearance of physical structures
or form.
 Morphological divergence – change from the body form of a
common ancestor.
o Homologous structures – structures that appear similar
in separate organisms because they evolved from a
common ancestor, may be used for different purposes
or functions, but the same genes direct their function.
 Morphological convergence body parts that you fall
independently in different lineages, subject to the same
environmental pressures. The structures are often called
analogous structures. Example: insect wings versus bird
wings.
PATTERNS OF EMBRYOLOGICAL DEVELOPMENT.
 Development of an embryo is conducted by master gene
expression master genes are highly conserved and direct
the steps in which an embryo will develop.
 Homeotic genes encode Transcription factors(on/off
switches for genes) that direct the details of the body’s
form during development.
o Somites- are divisions of the body, give rise to a
backbone.
o Hox genes- homeotic genes of animals, these master
genes determine the identity of particular zones along
the body axes, they appear in clusters along a crimson
in the order in which they are expressed during
development.
o Hox Genes are the same or similar in very different
organisms, meaning they are highly conserved.
Chapter 19
-The beginning
-Chemicals to cells
-Prokaryotes to Eukaryotes
BANG
 In a single instant, 13 to 15,000,000,000 years ago. All
matter energy suddenly appeared and exploded outward.
Elements such as hydrogen and helium formed within
minutes. Gases are together and contents to form giant
stars. Explosions of the stars scattered heavier elements
forming galaxies. The cloud of dust and rocks orbited the
star we call the sun. Asteroids collided and merged into
bigger asteroids material continue to gather until about 4.6
billion years ago enough material had together to form the
Earth.
 Now that’s what I call a big bang!
 Early Earth was a molten mass containing water vapor CO2
gaseous hydrogen and nitrogen, but little to no free oxygen
gas.
 As earth cooled water condensed into pools and seas.
CHEMICALS TO CELLS
 figuring out Earth’s 1st building blocks has been a daunting
task for many years, many theories have arisen, some of
them follow.
o Stanley Miller and Harold Urey hypothesis – whitening
could have power synthesis reactions in earth’s early
atmosphere. Space reaction chambers were filled with
gases believed to be present in the beginning.
PROBLEM. These gases probably did not represent the
early atmosphere.
o Guenter Wachtershauser and Claudia Huber
hypothesized life’s building blocks originated at deep
sea hydrothermal vents where mineral rich seawater
was heated by geothermal energy.
o Delivery from space – media rights delivered amino
acids should groups and nucleotide bases to the earth,
suggesting life’s building blocks have extraterrestrial
origins.
o Iron sulfur world hypothesis – (Guenter) 1st metabolic
reactions begin on the surface of rocks with iron
sulfide in the rocks donated electrons to dissolve
carbon monoxide...?
o RNA world hypothesis – RNA may have been the 1st
genetic material ribozymes (RNA’s that act like
enzymes) are common in living cells. (Reverse
transcriptase)
o Protocells-in membrane enclosed collection of
interacting molecules (Jack Szostak) David Deamer
studied protocell formation in the laboratory and in the
field where they can react with meteorite and
seawater to form vesicles with a bilayer membrane.
o Sequence for evolution cells from in organic molecules.
 In organic molecules.
 Organic monomers. [Self assembling in aquatic
environments]
 organic polymers [self assembly as vesicles, 1st
genome]
 proto-cells [membrane enclosed molecules that
take up material and replicates]
 DNA-based cells.
ORIGIN OF PROKARYOTES AND EUKARYOTES.
 How old is life on earth? That’s a good question!

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o Different methods of give different answers. 3.5
billion years ago to 4.3 billion years ago
The 1st organisms on earth were likely Chemoautotrophs,
which can use in organic compounds to create energy.
Many Archaebacteria are chemoautotrophs.
Photosynthetic bacteria likely evolved Next, using cyclic
pathway of photosynthesis.
Non-cyclic photosynthesis, then evolved in organisms like
cyanobacteria.
 Stromatolites- formed from mats of photosynthetic
bacteria with minerals and sediment trapped within were
prevalent at the time. They still grow today in shallow seas.
These types of organisms gave rise to our current oxygen
rich atmosphere.
 Endosymbiont hypothesis- states that mitochondria and
chloroplast evolved as a result of endosymbiosis, where one
organism lives inside of another organism. (but doesn’t that
sound like Lamarckism?)
 Evolution of Eukaryotes- a possible in folding of the plasma
membrane created the nuclear envelope and intermembrane
system.
 The first eukaryotes would have been protists, then giving
rise to fungi, plants and animals.
http://www.cengage.com/biology/book_content/9781111425692
_starr_udl13e/animations/PowerPoint_Lectures/chapter19/vid
eos_animations/tree_of_life.html
ALWAYS REMEMBER: Not knowing all the answers is ALWAYS
part of science and many things about the origin of life and
Earth may never be known.