population genetics

Unit 5 – Lecture 4

Darwin’s Five PointsObservations regarding natural selection:

populations have variationssome variations are beneficial / favorable

more offspring are produced than survivethose that survive will have favorable traitsbecause of this, a population will change

over time

Genetic EquilibriumRecall – natural selection affects

POPULATIONS not individuals

Gene Pool – the collection of genes within a populationallelic frequency – the frequency of certain

alleles within a population

Genetic Equilibrium – cont’dGenetic Equilibrium – a steady-state of

genetic material/information within a populationno new traits added, none removeddoesn’t really happen in nature

[will discuss why soon]

Genetic Equilibrium – cont’dHardy-Weinburg Law

can find out how many alleles are in population if you assume that there is genetic equilibrium at any single point in time

Discuss

List and explain Darwin’s Five Points.

Name and explain reasons why genetic equilibrium

does NOT exist in nature.

Genetic Equilibrium – cont’dGenetic Equilibrium could be achieved if:

there is a large breeding populationno selection

all traits must be as favorable than others to maintain the same amounts of each allele

random mating existsif there is sexual selection, certain traits

would be favorable…which would change the amounts of each allele in the population

Genetic Equilibrium – cont’dGenetic Equilibrium could be achieved if:

no change due to mutationsany loss or gain of alleles would

change the genetic ratiosno immigration or emigration

when organisms leave, they take with them their traits

when organisms arrive, they bring in new traits

Genetic Equilibrium – cont’dGenetic Equilibrium does not exist because of…

selectionnatural or otherwise –

changes amount of certain genesmutation

loss or gain of info – changes amount of certain genes

gene flowemigration / immigration

Genetic Equilibrium – cont’dGenetic Equilibrium does not exist because of…

genetic driftsmall populations exist in which certain genes

are more prevalent than in the general populusAmerican Indians do not have blood group BAmish – marry within their own community, so

more likely to have certain recessive conditions likepolydactyly [extra fingers]

Genetic Equilibrium – cont’dGenetic Equilibrium does not

exist because of…natural disasters /

mass illnesscause the

“bottleneck” effect

Discuss

Again, summarize the reasonswhy genetic equilibrium does NOT exist in nature.