uf bsc2010 exam 3 hart spring '26

Evolution

genetic changes in POPULATIONS over time

Theory of evolution

• supported by evidence

• parsimonious: simplest explanation

• falsifiable: make testable predictions

evidence of evolution

• fossil record

• molecular biology

• comparative anatomy (homologous anatomy)

Darwin’s inspiration

Lyell & Mathus

conditions of darwin’s natural selection

• variation in a trait

• heritable

• higher fitness

process of adaptation

beneficial mutations that evolve through natural selection

How are adaptations constrained

• genetic

• physical

• developmental

• ecological factors

darwin’s 3 conditions for evolution

• population has variation in a trait

• the variation is heritable

• high fitness

heritablity

proportion of total phenotypic variance that is due to genetic factors

gene flow

movement of genes between populations; introduces new alleles into population

genetic drift

random changes in allele frequency; affect smaller populations, due to random events like getting hit by a car

mutation

change in dna sequence; original source of all new genetic information

non-random mating

organisms choose mates based on certain traits; changes genotype frequencies

bottleneck population

an environmental event results in survival of only a few individuals; reduction in population size causes loss of genetic diversity and intensifies genetic drift

founder effect

when a few individuals from a population colonize a new area and become isolated, genetic drift changes allele frequencies

directional selection

favors individuals that vary in one direction from the mean; doesn’t change variance

stabilizing selection

favors average individuals; changes variance

disruptive selection

favors individuals that vary in both directions from the mean; increases variation

intrasexual selection

competing with same sex organisms for mates

intersexual selection

choosey about mates due to phenotypes

heterozygote advantage

individuals with heterozygote genotypes have higher fitness

negative frequency-dependent selection

rarer phenotypes have higher fitness, so multiple phenotypes are maintained

positive frequency-dependent selection

common phenotypes have higher fitness

genes

segment of dna

alleles

specific variant of gene

rare vs common alleles

one is rare one is not?

beneficial allele

these increase survival and fitness

deleterious allele

decrease survival and fitness

dominant alleles

A

recessive alleles

a

conditions for Hardy-Weinberg Equilibrium

• no mutation

• no selection

• random mating

• no gene flow

• infinite population size

Hardy-Weinberg Equilibrium

p= 2(N_AA)+ 1(N_Aa)/ 2(population)

q= 2(N_aa)+ 1(N_Aa)/ 2(population)

p²+2pq+q²=1

synonymous substitution

amino acid doesn’t change

nonsynonymous substitution

amino acid does change; can be advantageous, deleterious, or selectively neutral

positive selection

synonymous LESS than nonsynonymous

neutral selection

synonymous is EQUAL to nonsynonymous

purifying selection

synonymous is MORE than nonsynonymous

why is the neutral mutation rate independent of population size?

the variable for population size cancels out when calculating the mutation rate.

rate of fixation

lateral gene flow

individual genes, organelles, or genome fragments move horizontally from one lineage to another; bacteria uses this to increase resistance

gene duplication

a gene is duplicated, allowing one copy to mutate and evolve

two-fold cost of sex

cost of meiosis: females pass on 50% of her genes

cost of males: dividing off-spring into genders reduces female’s reproductive rate

Linnaean taxonomic classification scheme

how scientists name and classify organisms based on shared characteristics

what are monophyletic groups?

a group of organisms descending from a SINGLE common ancestor

what are paraphyletic groups?

a group that includes some descendants of an common ancestor but not all

what are polyphyletic groups?

a group that does not include the common ancestor

ancestral traits

trait found in common ancestor of two or more species; present in outgroup

derived traits

a trait that evolved later

monophyletic groups vs clades

same thing; clades used in phylogenetics

homologous traits

same structure due to common ancestry

analogous traits

similar function, different ancestry

parsimony principle

tree with fewest changes/ simplest form

synamorphy

shared derived trait found in more recent evolved species and groups; not present in earlier lineage

homoplasy

trait that looks similar but did not come from common ancestor; caused by convergent evolution and reversals

phylogenetic trees

built based on shared characteristics; following the parsimony principle

convergent evolution

when superficially similar traits may evolve independently in different lineages

evolutionary reversal

when a reverts from its derived state to its ancestral state

molecular clock

estimates divergence time by using constant rate of neutral mutations to measure how long two lineages have been evolving independently

molecular clock equation

T= D/2r

T=divergence time D=# of differences r=mutation rate

cryptic species

species that look VERY similar but don’t mate

morphological species concept

group of organisms that look similar; limited by cryptic species, regional variation and sexual dimorphism

biological species concept

groups of organisms that CAN mate together; limited by asexual & extinct species, and hybridization

lineage species concept

group of organisms that share a branch on the tree of life; requires phylogeny; species can interbreed, but offspring may be considered a new species based on genetic divergence

reproductive isolation

two species can’t successfully mate because of biological differences; makes sure lineages stay distinct, and all species can’t mate

allopatric speciation

populations are separated by a physical/geographical barrier; evolve through genetic drift

sympatric speciation

speciation without physical barriers/isolation; occur with disruptive selection and assortative mating

pre-zygotic isolation

isolation BEFORE egg fertilization; happens by temporal (time), habitat, mechanical, behavioral, and gametic isolation

post-zygotic isolation

isolation AFTER egg fertilization; happens b/c offspring doesn’t survive or reproduce

reinforcement

prevents hybridization from happening

things that affect speciation

• dispersal ability

• degree of specialization

• sexual selection

• environmental stability

adaptive radiation

rapid evolution of species from one ancestor; caused by little competition and threats;

rapid proliferation

outcome of adaptive radiation

how is an organism likely to become a fossil

organisms with hard skeletons or exo-skeleton

how are fossils formed

• at sites with no oxygen or heat

• typically found in sedimentary rocks

stratigraphy

how geologist estimate age of rocks; younger layers on top of older

major geological & atmospheric forces that affect earth history

tectonic plates, oxygenation, climate change, mass extinctions, and volcanic activity

radiometric dating

how geologists determine actual age of rocks

continental drift

position of continents change due to movement of tectonic plates

Pre-cambrian Era

4.2 bya - 542 mya; life appeared; eukaryotes evolved

Paleozoic Era: Cambrian period and on

542 mya - 251 mya; age of fishes, cambrian explosion: rapid diversification of multicellular life; massive extinctions, first plants and insects; swamps and forests

Mesozoic Era

251 - 65 mya; first dinosaurs, flowers, and snakes;

Cenozoic Era

65 mya - present; grasslands spread; plants and mammals diversify rapidly; multiple ice ages; many large mammals went extinct