AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

HARDY-WEINBERG LAW-MULTIPLE ALLELES

• If dominance is lacking, calculation of gene frequency is simple in multiple allelic systems.
• The best gene frequency estimate comes from simple gene counting.
• For example, in European cattle breeds, three transferrin alleles A, D and E occur.
• No dominance exists and so six genotypes can be distinguished, i.e., AA, AD, AE, DD, DE and EE.
• If we let these symbols denote the numbers of each genotype and N denotes the total number, we may calculate the gene frequencies as follows:

• For a three allele system, the equilibrium genotype frequencies can be expressed algebraically as p + q + r = 1

(p + q + r) ² = p² + q² + r² + 2pq + 2pr + 2qr = 1

• The ABO blood groups in man are determined by a series of three multiple allelic genes: A, B and O alleles.
• If there is dominance, then the estimation is slightly complicated, and approximate methods have to be used.