AP Biology Exam Review 2002-2003 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 drift Changes 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