Variation and mutation

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Slide 24

Math of HWE

And, because with two alleles we have three genotypes:

pp, pq, and qq

The frequencies of these genotypes are equal to (p + q)2 = 12

Or, p2 + 2pq + q2 = 1

Slide 25

Example of HWE Math

Local population of butterflies has 50 individuals

How many alleles are in the population at one locus?

If the distribution of genotype frequencies is 10 AA, 20 Aa, 20 aa, what are the frequencies of the two alleles?

Slide 26

Example of HWE math

With 50 individuals, there are 100 alleles

Each AA individual has 2 A’s, for a total of 20. Each Aa individual has 1 A, for a total of 20. Total number of A = 40, out of 100, p = 0.40

Each Aa has 1 a, = 20, plus 2 a’s for each aa (=40), = 60/100 a, q = 0.60

(Or , q = 1 - p = 1 - 0.40 = 0.60)

Slide 27

Example of HWE math

What are the expected genotype frequencies after one generation? (Assume no evolutionary agents are acting!)

Slide 28

Example of HWE math

What are the expected genotype frequencies after one generation? (Assume no evolutionary agents are acting!)

p2 + 2pq + q2 = 1 and p = 0.40 and q = 0.60

Slide 29

Example of HWE math

What are the expected genotype frequencies after one generation? (Assume no evolutionary agents are acting!)

p2 + 2pq + q2 = 1 and p = 0.40 and q = 0.60

AA = (0.40) X (0.40) = 0.16

Aa = 2 X (0.40) X (0.60) = 0.48

aa = (0.60) X (0.60) = 0.36

Slide 30

Mutation

Mutation is the source of genetic variation!

No other source for entirely new alleles

Slide 31

Rates of mutation

Vary widely across:

Species

Genes

Loci (plural of locus)

Environments

Slide 32

Rates of mutation

Measured by phenotypic effects in humans:

Rate of 10-6 to 10-5 per gamete per generation

Total number of genes?

Estimates range from about 30,000 to over 100,000!

Nearly everyone is a mutant!

Slide 33

Rates of mutation

Mutation rate of the HIV–AIDS virus:

One error every 104 to 105 base pairs

Size of the HIV–AIDS genome: