Module 1: Evolution

Gradualism

James Hutton's theory that evolution occurs slowly but steadily

population

# of organisms of the same species that live in a specific geographical area @ the same time & can potentially interbreed

sexual dimorphism

(lit: 2 forms) difference in appearance b/n male & females of 1 species based on primary & secondary reproductive organs/sexual *connection to sexual selection* → males w the most apparent signs of sexual dimorphism are often considered the most attractive to females - these male's traits will be reinforced over the next gens - the female's alleles that influence her to chose this type of mate will also be reinforced It is hypothesized that females choose mates this way bc the physical traits that influence their choices are often correlated w the male's health aka "good genes"

mutation

*a change in the genetic information encoded in the nucleotide sequence of DNA* - generally deleterious ; occasionally can make an organism "more fit" - only mutations in cells that produce gametes can be passed to offspring/affect genetic variability (in multicellular organisms) - mutation that affects a protein's function will probably be harmful - chromosomal mutations that delete, disrupt, or rearrange gene loci at once are almost certain to be harmful - prokaryote mutations generate genetic variation very fast bc bacteria multiply so rapidly -- Bacteria are haploid → new allele can have immediate effects -- mutation rates in plants/animals average about 1-10,000 - no new mutation → no new alleles

natural selection

*individuals w certain traits are more likely to survive/reproduce than individuals who w/o these traits* - usually takes hundreds of years to develop differences - occurs in interactions b/n individual organisms & the environment -- The population evolves, not the individual - amplifies or diminishes the heritable traits - not a goal that leads to the perfectly adapted organisms - descendants of ancestral populations spread into other habitats & adapt to fit their surroundings -- Focused on traits & "fitness" --- enviro selective pressure will change therefore there is no predetermined goal/outcome --- resource scarcity & excessive fecundity→ lots of competition --- offspring are like parents in their traits but not identical *most dynamic influencer of allelic frequency* → - the process of natural selection is not random ; leads to adaptive evolution - *Selected Alleles* : natural selection consistently favors alleles that improves the match b/n organism & environment - *Environments Change* → "good match" is a moving target → adaptive evolution is a continuous, dynamic process - *Relative Fitness* → the contribution an individual makes to the gene pool of the next gen relative to the contributions of other individuals -- "fittest individuals" are those that produce the largest # of viable, fertile offspring → pass on the most genes to the next gen

allele

1 of 2+ alternative forms of a gene that arise by mutation ; found @ the same place on a chromosome

why evolution can't make the perfect organism

1. Selection can only act on existing variations - Favors the fittest variants from the phenotypes that are available - These may not be the ideal traits 2. Evolution is limited by historical constraints - Evolution cant scrap ancestral anatomy & build new complex structures from scratch 3. Adaptations are often compromises 4. Chance, natural selection, & the environment interact - Chance events often affect the genetic makeup of populations - Genetic drift can result in the loss of beneficial alleles - Environment may change unpredictably from year to year

Uniformitarianism

Charles Lyell's idea that geologic processes have not changed throughout Earth's history

sexual reproduction

Components → - crossing over / recombination - independent orientation of homologous chromosomes @ metaphase I of meiosis - random fertilization *components create new assortments of existing alleles every generation* *Sex has a 50% cost in terms of genes passed down every gen* - Benefit is variation during meiosis, pairs of homologous chromosomes trade some of their genes by crossing over (1 chromosome per parent) each zygote made by a mating pair has a unique assortment of alleles Duplication of a gene or small pieces of DNA through errors in meiosis can provide an important source of genetic variation → may have played a major role in evolution

taxonomy

The scientific study of how living things are classified

heterozygous

a gene with a recessive and dominant allele Dd

sexual selection

a form of natural selection where individuals w certain traits are more likely than others to obtain mates

homozygous

a gene where the two alleles are both dominant /recessive DD or dd

genotype

an organism's genetic makeup, or allele combinations

genetic drift

chance events can cause allele frequencies to fluctuate unpredictably from 1 gen to the next *types* → 1. Bottleneck Effect → drastic reduction in population size (caused possibly by natural disasters) - Certain alleles may be present @ higher frequency in the surviving population vs the OG - other alleles may be present at lower frequency - some alleles might not be present at all - genetic drift may continue for many gens until the population retains a size for fluctuations due to chance to have less of an impact -- populations that retain a large enough after reduction may still have low levels of genetic variation - human activities (over-hunting/fishing, habitat destruction) can create severe bottlenecks for other species 2. Founder Effect → few individuals colonizing a new, isolated habitat - the smaller the group → < likely that its genetic makeup will represent the gene pool of the larger population it was previously apart of - requires migration followed by isolation 3. Gene Flow → a population gaining/losing alleles when fertile individuals move in/out of given population OR when gametes are transferred b/n populations

fossil record

chronicle of evolution over millions of years of geologic time engraved in the order in which fossils appear in rock strata - helped reemphasize Darwin's evolutionary theory problems: - Not all organisms lived in areas where they could be fossilized - Some fossils that did form were distorted/destroyed by geological processes - not all fossils are accessible - some fossils can be missleading -- there is no clear direction, the evolution tree has a lot of dead end branches

Hardy-Weinberg equilibrium equation

developed a base scenario which allows biologists to explain why/how evolution occurs no matter how many times alleles are segregated into diff gametes & united in different combinations by fertilization, the frequency of each allele in the gene pool will remain constant unless other factors are operating equation → *p^2 + 2pq + q^2 = 1* - allele frequencies p (homo) & q (hetero) must equal 1 & be followed through many generations *Conditions* → 1. Large Population - small population → allele frequency fluctuations ; creates genetic drift 2. No Gene Flow b/n Populations - moving in/out of populations → add/remove alleles 3. No Mutations - changing alleles/deleting duplicating genes modify gene pool 4. Random Mating - Inbreeding prevents genotype gamete mixing 5. No Natural Selection unequal survival/reproductive success alters allele frequency All 5 conditions are rarely met in real populations - allele/genotype frequencies often change

intrasexual selection

direct competition b/n individuals of the same sex & in the same species for a mate when male competition is involved, males are usually stronger/larger

stabilizing selection

favors intermediate phenotypes - Removes extreme phenotypes ex: birth weights of most human babies are b/n 6-8 pounds ; babies born out of that range are < likely to survive

intersexual selection

individuals of 1 sex (usually females) choose their mate

evolution

living species are descendants of ancestral species that were different from present-day ones

disruptive selection

occurs when environmental conditions vary in a way that favors individuals @ both ends of a phenotypic range over individuals w intermediate phenotypes - Favors extreme phenotypes - Leads to 2+ contrasting phenotypes in the same population ex: African black-bellied finches w small beaks or large beaks are more likely to survive compared to those w medium sized beaks bc the extremes are equipped for specific functions of survival

hemizygous

only 1 copy of an allele d or D

phenotype

physical manifestation of genotype in response to environmental conditions

artificial selection

selective breeding of domesticated plants/animals to promote the occurrence of desirable trains in the offspring - This was the key to understanding evolutionary change - Components : variation & heritability - Relatively short period of time to demonstrate trait differences evolution in real time → breeding provides a situation where people can manipulate the variations in the offspring of species - can demonstrate much change in a relatively short period of time

directional selection

shifts overall makeup of the population by acting against individuals @ 1 of the phenotypic extremes - common when a population's environment changes - *or* when members of a population migrate to a different habitat ex: in a population of cliff swallows, birds w larger bodies survived an unusual period of cold winter compared to others

homology

similarities resulting from common ancestry bc evolution is a remodeling process, related species can have characteristics that have an underlying similarity despite functioning differently homologous structures: Anatomical similarities b/n different organisms molecular homology: Inherited DNA of organisms from their ancestors - discovered by similar genes b/n different species - all life forms use the same genetic coding: DNA & RNA - Quantifiable - less likely to be analogous vestigial structure: leftover structures that have little/no importance evolutionary tree: diagram with multiple branches all connecting retracing to one trunk to represent the development of life -other- Analogy → similarities due to similar selective pressures analogies b/n 2 species does not necessarily = close common ancestor

microeveolution

smaller *changes in allele frequencies* causing each generation to be better adapted

gene pool

stock of different genes (every allele type) for every locus for an interbreeding population diversity in the gene pool is brought about by variation sources of variation → - mutation - sexual reproduction - horizontal evolution

preserving diversity in gene pools

tendency for natural selection to reduce variation in a population is countered by mechanisms that that maintain variation - bc most eukaryotes are Diploid (two alleles) 1. "hiding" a recessive allele in heterozygotes can maintain a huge pool of alleles that may not be favored under present conditions but have potential to be advantageous if the environment changes 2. Balancing selection → natural selection maintains stable frequencies of 2+ phenotypic forms in a population - Heterozygote advantage → type of balancing selection where heterozygous individuals have > reproductive success than either type of homozygote - Result: 2+ alleles for a gene are maintained in the population 3. frequency-dependency: evolutionary process by which the fitness of a phenotype depends on its frequency relative to other phenotypes in a given population - (+) frequency-dependent selection → fitness of a phenotype increases as it becomes more common - (-) frequency-dependent selection → fitness of a phenotype decreases as it becomes more common

dominant

the first allele of one gene ; expressed

horizontal evolution

the result of lateral gene transfer - randomly picking up alleles from enviro - mostly w prokaryotes

recessive

the second allele of one gene ; hidden - only appear when there is no dominant allele

gene

unit of inheritance that programs the amino acid sequence of a polypeptide - consist of DNA (deoxyribonucleic acid) : 1 of the 2 nucleic acid polymers RNA is another nucleic acid polymer