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

POPULATION MEAN

• Consider the following assumption:
  • Diploid organism
  • Diallelic autosomal locus
  • Random mating population
• The mean phenotype is obtained by summing the frequency weighted genotypic values (assuming that the environmental deviation is zero for each genotype).
• Let the gene frequency of A₁ and A₂ be p and q

Genotype	Frequency	Genotypic value	Frequency-weighted genotypic value
A1 A1	p2	+a	p2a
A1 A2	2pq	d	2pqd
A2 A2	q2	-a	- q2a
Total			a(p-q)+2pqd

• The contribution of any locus to the population mean has two terms: a (p-q) attributable to the homozygote and 2pqd attributable to heterozygote.
• With additive combinations the population mean value resulting from the joint effects of several loci is the sum of the contributions of each locus.
  • Population mean (M) = Σ a (p - q) + 2 Σ pqd
• Population Mean Genotypic Value is a function allele frequency. This Population Mean Genotypic Value is identical to the population mean phenotypic value if the mean environmental deviation is zero.