L16: Population genetics

natural selection

• process in which conditions of a habitat will naturally select for characteristics that will increase the chances of survival and reproductive success of organisms in a specific environment

• drives evolutionary change

what does natural selection act on

variation that already exists within a pop

what could darwin not explain

source of this variation as the role of genetics in evolution was not known at the time

population genetics

application of principles of mendelian genetics to populations to understand the process of genetics variation and speciation

neo darwinism

union of population genetics with the darwin theory of natural selection to view the evolutionary process

population

group of individuals from the same species that live in the same geographical area and that actually or potentially interbreed

area where pops are found

considered to be of a size which individuals in the pop are likely to find mates

subpopulation

• geographically widespread areas divided into more or less distinct breeding groups that live within limited geographical areas

• aka local pop

gene pool

• genetic info carried by all members of a pop

• includes all alleles present in the gametes made by all the breeding members of a pop in a single gen

allele frequency

• the pop of gametes in a gene pool that carry a particular allele represents the frequency with which this allele occurs in the pop

• propo of all alleles that are of the specified type in a pop

genotype frequency

propo of organisms that have a particular genotype

uses of allele frequences

• used to make inferences about matings in a pop

• predicts the genetic compo of future gens

• more useful than genetic f becuase genes (haploid), not genotypes, form the bridge between gens

what should allele and genotype f be between

0 and 1

allele f of 1

the allele is said to be fixed in the pop

allele f of 0

the allele is said to be lost from the pop

hardy-weinberg law

states that the allele f in a large pop inhabiting a common area remain constant from gen to gen unless disturbed by other influences

influences that may disturb hardy-weinberg eqm

• non random mating

• mutations

• selection

• limited pop size

• random genetics drift

• gene flow

consequences of hardy weinberg model

• dom traits fo not necessarily increase from one gen to next

• genetic variabilty can be maintained in a pop, since once established in a pop, allele f must remain constant

• knowing the f of one genotype allows us to calculate the f of all other genotypes at that locus

assumptions of hardy-weinberg

• pop size is sufficiently large - f of alleles do not change from gen to gen (no genetic drift observed)

• mating is random - no subpop differ in allele f

• mutation does not occur

• migation into the pop does not occur

• all genotypes are equal in viability and fertility - natural selction does not occur

inbreeding

• non random mating

• increases the propo of homozygotes and decreases the propo of heterozygotes

• can change the f of genotypes in a pop but not the allele f

• disturbs hardy-weinberg

a completely inbred pop

only consist of homozygous genotypes

harms of inbreeding

increases the prob that the number individuals homozygous for deleterious or lethal alleles will increase in pop

sum of allele f

p+q = 1

distribution of genotype f among zygotes as per hardy-weinberg

p² + 2pq + q² = 1

pops where allele f remain constant from gen to gen

• said to be in a state of hardy-weinberg eqm for that locus

• genotypes f can be predicted from the allele f

expected ratio of f where pop mate at random

p² : 2pq : q²

when is the f of heterozygotes the highest (allele f)

when p = q = 1/2