L19 Natural selection

Forces of evolution

Gene flow, random genetic drift, natural selection

allele frequency

relative frequency of an allele at a particular locus in population

New mutation arises in pop of 100 bunnies (200 for chromosomes for diploid)

1/200

Random genetic drift

Random changes in allele freq

besides bottle neck, and founder effect

most mutations are lost to drift

Natural selection

Mutations may make an individual more or less likely to survive and reproduce

post survival dont matta WHOEVER FUCKS THE OST

Reproductive success

Natural selection works to increase fitness, not health

Fitness doesn’t mean in good shape

Fitness average reproductive success of individuals with a given trait

Negative selection (purification)

Removes deleterious mutations detectable as lack of variation

Positive selection

Increases frequency of beneficial mutation can be hard of soft decreases variation

Balancing selection

Increases diversity , selection to maintain balance of ales

common alleles are under strongest negative pathogenic pressure, driving positive selection of uncommon alleles

Selective sweep

how a new beneficial mutation increases in frequency to become fixed in population

Reduced or eliminated of genetic variation near the mutation

Positive selection causes new mutation to reach fixation so quickly linked to alleles hiking

Selective sweep process

1. Take sequences from pop

2. look at the beneficial mutation

3. Beneficial mutation increases in frequency in the population and so does genomic background

4. Recombination event renders no longer associated with/ mutation

5. A beneficial mutation is fixed in the population. Close to the beneficial mutation, there is now no genetic variation left, all 3 look the same. 3 neutral mutations have hitchhiked along with beneficial and reached high frequency

Convergent evolution

Phenomenon in which organisms or populations not closely related independently evolve similar traits

Lactose persistence

Various autosomal dominant alleles prolong lactase beyond infancy, lactose intolerance, adult lactase persistence in Africans, marked example of convergent evolution due to strong selective pressure resulting from shared culture domestication

Ancestral skin color

Before losing fur, monkeys were likely light-skinned, afterwards, archaic humans were dark-skinned

After migrating out of Africa some northern populations experienced positive selection

UV radiation, vitamin D

High UVR near the equator led to evolution of dark, photoprotective eumelanin-rich pigmentation

Low UVr elsewhere and need for UVB photons to sustain cutaneous photosynthesis of vitamin d3 resulted in evolution of depigmented skin