Polygenic inheritance

Definition

• Polygeny is when a single characteristic may be controlled by more than one gene.

Several genes control the expression of the same character

• These types of phenotype exhibit continuous variation in a population.– Eg skin colour, height

Skin colour

• 5 possible phenotypes

• 9 genotypes

• Melanin production is controlled by 2 genes

• The amount is directly proportional to the number of dominant alleles

• White - 0

• Light - 1

• Medium – 2

• Dark – 3

• Black – 4

• Complete the punnett square for a heterozygous cross writing in the genotype and phenotype.

Activities

• Determine the phenotypes of the offspring for the following:– A mating of white with black– A mating between two individuals of medium

skin colour

• If 5 phenotypes are possible for two genes, how many are possible for three (eg A, B and C)

• What is the difference between continuous and discontinuous variation?