Evolution and
Classification
Jeffery Ha, Raj Iyer, Balu Kurup, Rishi
Wagle B3
Evolution
★ Darwin’s principle of Natural Selection
a. Variation - individuals within a population possess heritable variation within traits
Sexual recombination and Mutations.
b. Overproduction- organisms produce more organisms than can survive.
c. Competition- those with suitable adaptations will outcompete others.
d. Differential Survival- Those with suitable characteristics tend to survive more.
e. Differential Reproduction- those with favorable traits will survive and pass on the
traits to their offspring
Individuals do not evolve, but populations do!!
Selection Mechanisms
a. Directional- those at one end of the spectrum is favored so the graph shifts
Disruptive- those at each ends are selected, the median is not favored.
Stabilizing- those in the median area is favored.
a. Sexual selection- preference of certain characteristic in the opposite sex.
c. Genetic drift- successful organisms may leave genes behind
Bottleneck Effect- an event that reduces population to small numbers and variation
in species.
Founder Effect- loss of genetic material upon introduction of a new species.
d. Gene Flow - transfer of genes from one population to another, creates genetic
variation.
Lines of Evidence for Evolution
1. Fossil Record- buried fossils of organisms and ancestors
2. Biogeography- how the species were distributed across the world
3. Convergent evolution- not closely related organisms develop similar traits due to
their environments and adaptations.
4. Comparative anatomy- study of body structures of different species.
5. Homologous structures- similar body structures in different species due to a
common ancestor.
6. Comparative embryology- similarities and differences among embryos of different
organisms.
7. Artificial selection- breeders selectively breed based on certain desired traits (dog
breeding, crops, babies)
Hardy-Weinberg Equilibrium
● Equations
o
o
p+q=1
p2 + 2pq + q2 = 1
● Conditions
o
o
o
o
o
Infinitely large population
Random mating
No mutations
No gene flow (migration)
No selection
Speciation
● Ernst Mayr developed biological species concept
(BSC)-a species is a population that can interbreed and
produce viable, fertile offspring
● Types of speciation:
o Allopatric-geographically isolated populations
o Sympatric-populations in the same environment adapt to
different niches; incl. adaptive radiation (organisms diversify
into many new forms)
Speciation (cont.)
● Mechanisms for speciation:
o Pre-zygotic: habitat factors, temporal factors, behavioral factors,
mechanical factors, gamete factors
o Post-zygotic: reduced hybrid variability, reduced hybrid fertility
● Rate of speciation:
o Gradualism-change is the product of slow but continuous processes
o Punctuated equilibrium-species stay the same for a long time,
followed by periodic outbursts of change
Origin of Life
● Earth is 4.5 billion years old
● Abiotic origins of Earth
o
o
o
Atmosphere contained CO2, CH3, and NH3 which
was energized by lightning and UV rays and resulted
in formation of organic compounds
Same idea was shown in the Miller experiment
This led to the formation of protobionts and later
bacteria around 3.5 billion years ago
Miller Experiment
Domains
● Cladograms, or phylogeny trees, illustrate
the relationship between the 3 domains
● The 3 domains are eubacteria,
archaebacteria, and eukarya
Characteristics and Examples of Each Domain
● Bacteria (eubacteria) : unicellular prokaryotes, no membrane
bound organelles, single circular chromosome, peptidoglycan cell
wall, asexual reproduction; Ex: Bacillus, Streptococcus
● Archaebacteria : unicellular prokaryotes, cell wall, cell membrane,
ribosomes, no membrane bound organelles, DNA + histone
proteins, single circular chromosome, asexual reproduction; Ex:
Methanococcus, Halobacterium
● Eukarya : unicellular & multicellular eukaryotes, membrane bound
organelles, nucleus, mitochondria, chloroplasts, Golgi apparatus,
ER, lysosomes; Ex: animals, plants, fungi
Eukaryotic Kingdoms
● Protista are either autotrophs or heterotrophs, and only some have cell
walls and cell membranes. They reproduce mainly through asexual
methods such as binary fission and budding. They are mostly unicellular,
and move via flagella and cilia
● Fungi are heterotrophs which use absorption with cell walls composed of
chitin. They reproduce through mostly sexual methods, except for
unicellular yeast. Examples include yeast and mushrooms
● Plantae are autotrophs which utilize photosynthesis with cell walls
composed of cellulose. They reproduce through sexual and asexual
methods, and include mosses, ferns, gymnosperms, and angiosperms
● Animalia are heterotrophs without cell walls, and they reproduce sexually.
They include all multicellular organisms, invertebrates, and vertebrates.
Eukaryotes: Plants
Eukaryotes- Animals
Animals- Mammal Subgroups
● Monotremes- egg-laying mammals with no
mammary glands, e.g. duck-billed platypus,
echidna
● Marsupials- pouched mammals, e.g.
kangaroo, koala
● Placentals- fully developed placenta, e.g.
rodents, primates, canines, felines
FRQ: 2001 AP Biology Exam, Question 2
Intro: Charles Darwin proposed that evolution
by natural selection was the basis for the
differences that he saw in similar organisms as
he traveled and collected specimens in South
America and on the Galapagos Islands.
FRQ: Part A
A. Explain the theory of evolution by natural
selection as presented by Darwin.
FRQ: Part B
B. Each of the following relates to an aspect of evolution
by natural selection. Explain 3 of the following.
i. Convergent evolution and the similarities among species in a particular
biome
ii. Natural selection and formation of insecticide-resistant insects or
antibiotic-resistant bacteria
iii. Speciation and isolation
iv. Natural selection and behavior incl. kinesis, fixed-action-pattern,
dominance hierarchy, etc.
v. Natural selection and heterozygote advantage
Answer to Part A
A. Explain the theory of evolution by natural selection as presented by
Darwin. (worth 6 pts; each concept below worth 1 pt)
Reproductive potential: the ability to over produce
Variability: inheritable changes or mutations linked to variability
Limited resources: biotic or abiotic
Competition: intraspecific struggle for existence
Differential Reproduction: reproductive success of variants
Generations: time needed for evolution to occur
Elaboration: expansion of Darwin’s ideas such as the effects of environmental change or artificial
selection or good, linked example
Answers to Part B
B. Explain three of the following. (2 pts, per section of B)
i. Convergent evolution and similarities among species in a particular biome
- Different species exhibit adaptations as a result of the same environment
- Correct descriptive example linked to biome and survival value or linked to natural selection
ii. Natural selection and the formation of insecticide-resistant insects or antibiotic-resistant
bacteria
- An inherited characteristic enables the organism to resist the effect of the toxin
- Specific example, mechanisms of resistance, or extensive elaboration or link to natural
selection
Answers to Part B (cont.)
B. Explain three of the following. (2 pts, per section of B)
iii. Speciation and isolation
- A single population divides into two reproductively isolated populations or equivalent (use of
gene pools)
- Role of barriers in speciation or discuss gene pool separation or link to natural selection
iv. Natural selection and behavior
- Define or describe the behavior
- Give a clear example of how this behavior enhances survival or link to natural selection
v. Natural selection and heterozygote advantage
- Survival value of heterozygote over both homozygotes
- An example of how the heterozygous enhances the survival of the organism or link to natural
selection