AP Biology Exam Review2002-2003

Heredity and Evolution – 25%

Evolutionary biology – 8% Early evolution of life Evidence of evolution Mechanisms of evolution

Related fields of study Paleontology: study of fossils Comparative anatomy: study of structural

similarities among organisms Comparative embryology: study of

embryological similarities among organisms Taxonomy: study of organism groupings

with similar homologous structures (including vestigial organs)

Biochemistry: chemical reactions in living things

Terminology Population: localized group of

individuals of the same species

Species: group of population whose individuals have the potential to interbreed and produce fertile offspring

Gene pool: total aggregate of all genes in a population at any given time

Tenets of evolution Natural selection “edits” the available

gene pool for a species. Natural selection is contingent upon

time and place. Certain variations in a population (group of species residing in one area) are more favored for survival than others.

Mutations are a sources of variation in a population.

“Descent with modification”

DDT & Insects

Insects with DDT resistance also have reduced metabolism.

Without DDT present, these insects are not adapted for the environment.

Homology vs. Analogy

Three kinds of homologies – having common origin 1. Anatomical homology: example,

forelimbs

2. Embryological homology: example, Eustachian tube in humans and all mammals

3. Molecular homology: DNA, RNA as genetic code (shown through RFLP analysis)

Molecular homology

Human hemoglobin has 146 amino acids total.

Sugar glider vs. Flying squirrel

Convergent evolution

Genetic driftChanges to allele frequencies in population due to random chance

Bottleneck effect Genetic drift due to drastic reduction in

allele frequencies

What factors can cause bottleneck effect?

The founder effect Members from a larger population

colonize an isolated region. (Ex: primary, secondary succession)

Ex: 15 people founded a British colony in 1814, midway in the Atlantic Ocean. One colonist had retinitis pigmentosa, a recessive degenerative blindness. Today, there is a higher frequency of this disorder than most places on Earth.

Gene flow Genetic exchange due to migration

of fertile individuals or gametes between populations

Ex: wind carrying pollen grains with sperm from plant to far off locations

Mutations Changes to an organism’s DNA

Changes in the DNA, if occurring in gametes, can be passed down to the next generation.

Quantitative changes to the population can only result if organisms with the mutation produce a disproportionate number of offspring.

Variations in the population Polymorphism: For any

characteristic, there are more than two “morphs” (forms).

A variation of the characteristic can only be considered one of the morphs if there is a high enough frequency in the population.

Measuring diversity Gene diversity: measuring whole

gene differences

Nucleotide diversity: measuring differences at the molecular level (using RFLP analysis or genomic comparisons)

Geographic diversity Differences in gene pools between

populations or within subgroups of populations

Cline: graded change in some trait along a geographic axis

Cline

What preserves variation Mutation Sexual recombination (meiosis) Diploidy Balanced polymorphism: ability to

maintain stable allele frequency (established through heterozygote advantage and frequency-dependent selection)

Neutral variation

Directional selection

Limitations of natural selection 1. Limited to historical constraints

2. Adaptations are often compromises.

3. Not all evolution is adaptive.

4. Selection can only edit existing variations.

Hardy-Weinberg equation of non-evolution No natural selection No mutation No migration Large population Random mating

p2 + 2pq + q2 = 1 p + q = 1

Hardy-Weinberg equation p = frequency of dominant allele in the

population (A) q = frequency of recessive allele in the

population

p2 = AA (homozygous dominant genotype) 2pq = Aa (heterozygous genotype) q2 = aa (homozygous recessive genotype)

p2 + 2pq = dominant phenotype q2 = recessive phenotype

Sample H-W problem Hint to solving these equations: LOOK FOR

THE PERFECT SQUARE!! SOLVE FOR Q!

In a population of 100 individuals, 91 in the population show the dominant phenotype. What is the frequency of the dominant allele in this population?

(100 – 91)/100 = recessive phenotype = q2

.09 = q2 q = .3 p+q = 1 p = .7

The Origin of Species

In what circumstances would new species evolve from

preexisting species?

Reproductive barriers helps to preserve species. Any factors that impedes the

reproduction of members within a species

Without the ability to breed together, the gene pool is isolated. (no migration)

Two types of barriers Prezygotic barriers: prevents

fertilization of ova (egg)

Postzygotic barriers: following fertilization, hybrid zygote unable to develop into viable offspring

Prezygotic barriers Habitat isolation Behavioral isolation Temporal isolation Mechanical isolation Gametic isolation

Postzygotic barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown

Other definition of species Ecological: niche (set of

environmental resources an organism uses)

Pluralistic: more than one way to define species

Morphological: organisms with unique set of structural features

Geneological: organisms with unique genetic history

Interrupting gene flow Changes to the gene pool can

ultimately lead to evolution of new species.

This is called speciation.

Patterns of speciation Anagenesis:

phyletic evolution, accumulation of heritable change in a population

Cladogenesis: branching evolution, (basis for biological diversity)

*Three modes of speciation* Allopatric speciation: geographic

separation leads to new species if organisms evolve reproductive barriers

Sympatric speciation: small population within parent population becomes new species

Adaptive radiation: ancestral species colonize an area where diverse geographic or ecological conditions are available, rapid evolution

Allopatric vs. Sympatric What

factors can lead to each type of speciation?

Allopatric speciation Geographic barriers (mountains,

valleys, etc) can separate the ability for breeding between members of the same species.

Ring species: species that seemingly are in the gradual process of divergence from a common ancestor

Adaptive radiation Much like allopatric

speciation

Island chains have geographic isolation but are close enough for occasional have hybrids between populations.

How reproductive barriers evolve Diane Dodd’s experiment showing

allopatric speciation leading to reproductive barrier (therefore new

species)

Allopatric speciation

Sympatric speciation in plants Autopolyploid: organism with more

than normal chromosome # due to meiotic failures.

4N can breed with 4N 8N offspring (polyploid)

In one generation, postzygotic barriers form, causing reproductive isolation.

Allopolyploid Members of two different species create a

hybrid that cannot back breed with parents. The hybrid is more vigorous (*hybrid vigor*) enables hybrid to reproduce asexually may eventually evolve sexual reproduction.

Sympatric speciation Fishes in Lake Victoria (East Africa)

demonstrate that females may select mates based on coloration.

Overtime, the nonrandom mating leads to behavioral isolation, and a new species of fish arise within the parental population.

Punctuated equilibrium Sudden

appearance of organisms in the phylogenetic tree

Micro vs. Macroevolution Microevolution: changes in gene

(allelic) frequency over generations; Hardy & Weinberg

Macroevolution: level of change in organisms that is evident in the fossil record (requires long period of time)

Speciation bridges microevolution and macroevolution.

Patterns of evolution Divergent evolution: Two or more species

originate from the same ancestral species.

Convergent evolution: Two unrelated species share many characteristics.

Parallel evolution: Two related species after divergence evolve similar characteristics.

Coevolution: symbiotic relationships

Origin of life Oldest fossils = 3.5 billion years old,

indicating maybe oldest life form 1 billion years old

Cyanobacteria: earliest fossilized organisms

Common metabolic pathway in all organisms: glycolysis

Primitive atmosphere: hydrogen, methane, ammonia, water vapor (reducing atmosphere)

Chemical evolution 1. Earth and its atmosphere formed. 2. Primordial seas formed. 3. Complex molecules synthesized. 4. Polymers and self-replicating molecules were

synthesized. (proteinoids) 5. Organic molecules were concentrated and

isoaltred into protobionts. 6. Primitive heterotrophic prokaryotes formed. 7. Primitive autotrophic prokaryotes formed. 8. Oxygen and ozone layer formed. 9. Eukaryotes formed.

Endosymbiotic theory Mitochondria and chloroplast have

their own circular and “naked” DNA. M & C ribosomes similar to bacteria. M & C divide independently much

like binary fission. Thylakoid membranes of chloroplast

resemble membranes of cyanobacteria.

Origin of life experiments Oparin and Haldane: able to produce

coacervates that could take in enzymes; predicted simple molecules form when oxygen absent

Stanley Miller: able to synthesize simple organic compounds with flash of electricity (“lightning”); tested Oparin and Haldane’s hypotheses

Melvin Calvin: complex molecules formed from polymerization

Sidney Fox: microspheres (protenoids)

Chemical selection Aggregates with most stable

compounds remained.

Chemical reactions that preserved aggregates enabled aggregates to remain.

Nonliving living: able to store and use energy (metabolism), able to pass on genetic information

Hydrogen pumps Believed to be the first enzymatic

proteins (light-driven) to provide coacervate energy

ETC of respiration and photosynthesis formed

Why RNA before DNA RNA has extra –OH group on 2’

carbon.

It is able to bind amino acids to allow for translation (genetic material protein enzymes)

Earliest organisms May have been heterotrophs As O2 generated in atmosphere from

photodissociation (H2O) H2O2 may have formed killing off

heterotrophs Cyanobacteria increased in gene pool,

forming ozone layer. Aerobic respiration may have evolved. Heterotroph-autotroph hypothesis