HardyWeinberg Principle Learning Objectives Explain the HardyWeinberg principle

Hardy-Weinberg Principle

Learning Objectives • Explain the Hardy-Weinberg principle • List the five conditions needed to maintain genetic equilibrium

Hardy-Weinberg Principle Allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change.

5 Factors Required to Maintain Genetic Equilibrium 1. There must be random mating 2. The population must be very large 3. There can be no movement in or out of the population 4. No mutations 5. No natural selection

Hardy-Weinberg Equations We can use the Hardy-Weinberg equations to make predictions about the relative frequency of the different alleles

Hardy-Weinberg Equation #1 p = the frequency of the dominant allele (A) q = the frequency of the recessive allele (a) For a population in genetic equilibrium: p + q = 1. 0 (The sum of the frequencies of both alleles is 100%. )

Hardy-Weinberg Equation #2 p 2 = frequency of AA (homozygous dominant) 2 pq = frequency of Aa (heterozygous) q 2 = frequency of aa (homozygous recessive)

Hardy-Weinberg Practice Allele for black coat is recessive Calculate q 2 = frequency of aa (homozygous recessive) Count the number of black pigs. Calculate the % of total population they represent. q 2 = 4/16 or ¼ or 0. 25 or 25%

Hardy-Weinberg Practice q 2 = 0. 25 Calculate q q = the frequency of the recessive allele (a) Take the square root of q 2 q = 0. 5

Hardy-Weinberg Practice q = 0. 5 Calculate p p + q = 1. 0 p = the frequency of the dominant allele (A) p = 1 - 0. 5 p = 0. 5

Hardy-Weinberg Practice q = 0. 5 p = 0. 5 Calculate 2 pq = frequency of Aa (heterozygous) 2 pq = 2 x 0. 5 2 pq = 0. 5 or 50%

Hardy-Weinberg Practice p = 0. 5 Calculate p 2 = frequency of AA (homozygous dominant) p 2 = (0. 5) 2 p 2 = 0. 25 or 25%

Conclusions p 2 = % of AA (homozygous dominant) = 25% 2 pq = % of Aa (heterozygous) = 50% q 2 = % of aa (homozygous recessive) = 25%

Now you practice independently

In a certain population of 1000 fruit flies, 640 have red eyes while the remainder have sepia eyes. The sepia eye trait is recessive to red eyes. How many individuals would you expect to be homozygous for red eye color? Hint: The first step is always to calculate q 2 Start by determining the number of fruit flies that are homozygous recessive.

Within a population of butterflies, the color brown (B) is dominant over the color white (b). 40% of all butterflies are white. Calculate the following: The percentage of butterflies in the population that are heterozygous. The frequency of homozygous dominant individuals.

The frequency of two alleles in a gene pool is 0. 19 (A) and 0. 81(a). Assume that the population is in Hardy-Weinberg equilibrium. 1. Calculate the frequency of homozygous recessives in the population. 2. Calculate the frequency of heterozygous individuals in the population.

You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following: The frequency of the "aa" genotype. The frequency of the "a" allele. The frequency of the "A" allele. The frequencies of the genotypes "AA"