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Lecture 11

BGYB51H3 Lecture 11 Notes Oct 15

Biological Sciences
Course Code
Maydianne Andrade

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BGYB51H3 Lecture 11 Notes
-(o]}vUPv}Ç(µv]v[µo}2, 2pq, and q2
-allele frequencies change due to selection (see figure 6.12)
-in populations with 2 alleles, sum of allele frequencies and sum of genotype frequencies must
add up to 1
-selection on mutations causes evolutionary change
-under frequency dependent selection, the phenotype fitness depends on its frequency
(increase in frequency, decrease in fitness)
-frequency-dependent selection maintains genetic variation
-in heterozygote superiority (overdominance), heterozygotes have highest fitness so that both
alleles are maintained in the population
-one allele favoured involves rate of change depending on initial frequencies of each allele and
its dominance
-heterozygote inferiority means that fixation of one allele is possible depending on initial
frequencies and relative fitness of homozygotes
-heterozygote inferiority maintains variation among populations and not within populations
-frequency-dependent selection involves negative frequency dependence
-phenotypes with higher frequency in the population have lower frequency of breeding adults
in frequency dependent selection
-some alleles that are lethal are maintained because alleles are hidden from selection by
-homozygote recessive lethal alleles decrease dramatically
-at low frequencies of recessive, most copies are found in heterozygotes which will mate with
the dominant homozygotes
-deleterious alleles may persist under mutation-selection balance
-the higher the selection coefficient, the lower the fitness of the allele selected against
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