Population Genetics

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Slide 12

The Hardy-Weinberg Principle

Used to describe a non-evolving population.

Shuffling of alleles by meiosis and random fertilization have no effect on the overall gene pool.

Natural populations are NOT expected to actually be in Hardy-Weinberg equilibrium.

Slide 13

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The Hardy-Weinberg Principle

Deviation from Hardy-Weinberg equilibrium usually results in evolution

Understanding a non-evolving population, helps us to understand how evolution occurs

Slide 14

5 Assumptions of the H-W Principle

Large population size - small populations have fluctuations in allele frequencies (e.g., fire, storm).

No migration - immigrants can change the frequency of an allele by bringing in new alleles to a population.

No net mutations - if alleles change from one to another, this will change the frequency of those alleles

Slide 15

5 Assumptions of the H-W Principle

Random mating - if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.

No natural selection - if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

Slide 16

Traits Selected for Random Mating

Slide 17

The Hardy-Weinberg Principle

The gene pool of a NON-EVOLVING population remains CONSTANT over multiple generations (allele frequency doesn’t change)

The Hardy-Weinberg Equation:

1.0 = p2 + 2pq + q2

Where:

p2 = frequency of AA genotype

2pq = frequency of Aa

q2 = frequency of aa genotype

Slide 18

The Hardy-Weinberg Principle

Determining the Allele Frequency using Hardy-Weinberg:

1.0 = p + q

Where:

p = frequency of A allele

q = frequency of a allele

Slide 19

Allele Frequencies Define Gene Pools

As there are 1000 copies of the genes for color,

the allele frequencies are (in both males and females):

320 x 2 (RR) + 160 x 1 (Rr) = 800 R; 800/1000 = 0.8 (80%) R

160 x 1 (Rr) + 20 x 2 (rr) = 200 r; 200/1000 = 0.2 (20%) r

500 flowering plants

480 red flowers

20 white flowers

320 RR

160 Rr

20 rr

Slide 20