genetics chapters 25-26

population genetics

the genetic structure of populations and how they change geographically over time

mendelian population

group of interbreeding individuals who share a common set of genes

neo-Darwinian synthesis

fusion of Mendelian theory with Darwinian theory in the 1st half of the 1900s

foundation for modern biological thinking

genotypic frequencies

number of individuals with genotype / total in population

calculation used to study the genes of a particular gene pool by quantifying genotypes at a specific locus

the sum of genotypic frequencies for any given trait in a population

one

allele frequencies

calculated from number of diff genotypes at a locus

or

from genotypic proportions

Hardy-Weinberg Law assumptions

population is infinitely large

mating is random with regard to the trait(s)

no natural selection

no mutations

no migrations

Hardy-Weinberg Law predictions

the population is in genetic equilibrium when all assumptions are met

allele frequencies do not change over generations

after one generation, frequencies will be p², 2pq, and q², and remain constant

genetic drift

the random deviation of expected ratios due to small population size

cline

change in allele frequencies across a geographical transect, usually correlated with features such as temperature and rainfall

evolution

change in gene frequencies in a population

random genetic drift (sampling error)

random events in a population affect allele frequencies

effective population size (N_e)

number of adults that are contributing their gametes into the next generation

population bottlenecks & founder effects

when a population expands from a small number of ancestors

gene flow

gene movement, when genes are exchanged between populations, introducing new alleles and altering allele frequencies in recipient population

natural selection

heritable traits that increase an organism’s chance of survival will be favored in the environment and allow that individual to successfully reproduce more, and those traits will be passed on

directional selection

selection for or against a specific phenotype at one end of the spectrum

stabilizing selection

selection for an intermediate phenotype, extreme phenotypes are selected against

disruptive selection

selection for phenotypic extremes and selection against intermediates

positive assortative mating

when individuals prefer to mate with individuals that are phenotypically similar to themselves

negative assortative mating

when individuals prefer to mate with individuals that are phenotypically different from themselves

heterosis

heterozygote superiority, beneficial for hybrid crop growth

inbreeding

preferred mating between relatives, effects similar to drift in a small population

population viability analysis

estimates how large a population must be to prevent extinction over a particular period of time

speciation

when populations diverge to the point that they no longer interbreed, then different alleles become fixed over time

species

group of actually or potential interbreeding organisms

postzygotic

poor fitness of offspring (infertile), leads to prezygotic isolation

prezygotic

prevent mating by genetic discrimination, accelerates divergence

temporal isolation

different mating or activity periods

ecological isolation

different ecological niche

behavioral incompatibility

no mate recognition

mechanical isolation

genitalia don’t fit togetherq

gametic isolation

gametes don’t fuse properly

molecular evolution

examines how genes (DNA and proteins) change over evolutionary time

phylogenetic trees

branched diagram used to describe relationship between species

can be rooted to indicate ancestry for all members of the tree (+outgroup)

gene tree

represents the history of a gene, based on the divergence in a single homologous gene

species tree

uses data from many genes

inferred trees

many possible trees generated for a specific relationship