1. 10.3 Polygenic Inheritance
HL Material

2. Polygenic Inheritance
Concerns a single characteristic that is controlled by more than one gene
Each allele only contributes a small amount to the overall phenotype of the individual
The more genes involved, the more variation
examples: human skin colour, height, shape of comb in poultry

3. Polygenic Inheritance
Contributes to continuous variation rather than an either “on” or “off” version of the trait
a) Is the genotypic variation in the population. The more genes involved with the characteristic the greater the number of phenotypic classes.
(b) Phenotypic variation = genotypic variation + environmental variation. The environmental component smoothes the genotypic category differences.

4. Example: Skin Colour Controlled by as many as 4 genes
Alleles control the production of malanin (pigment that colours skin)
Example: two genes involved; two individuals heterozygous at both alleles
A: melanin (value of 1)
a: no melanin (value of 0)
B: melanin (value of 1)
b: no melanin (value of 0)

5. Parental Genotypes: AaBb x AaBb
Parental Gametes:
Set up a dihybrid cross

7. What happens if there are 3 genes involved?
Parental Genotype: AaBbCc x AaBbCc