1. Polygenic inheritance
Lots of genes can control one trait

2. Poly = Lots genic = genes
So far we’ve only looked at traits that are caused by 1 gene.
Some traits are caused by 2 or more genes.
This is called polygenic inheritance.
Eye colour ,skin colour, and hair colour are all polygenic.
This can get really complicated.

3. Usually these genes are all on different chromosomes.
Simple dominance = 2 phenotypes codominance = 3 Phenotypes Multiple Alleles = 4 phenotypes Polygenic = lots and lots of phenotypes
Usually these genes are all on different chromosomes.
Because there are so many possibilities of genotypic combinations there is often a wide variety of phenotypes.
In humans eye colour, hair colour, and height are examples of polygenic in heritance.

4. Hair is determined by 2 Genes
one colours the medulla of the hair shaft
(H= dark, h=light)
the other determines the colour of the
outer cortex (C=dark. c=light).

5. Genotypes Phenotypes
HHCC Black
HHCc Black
HHcc Red
HhCC Brown
HhCc Brown
Hhcc Regular blond
hhCC Dark blond
hhCc Regular blond
hhcc Pale blond

6. What are the possible phenotypes (hair colour) of the offspring?
If Hannah with pale blond hair had a baby with a man who was heterozygous for Medulla colour and homozygous dominant for outer cortex colour.
What are the possible phenotypes (hair colour) of the offspring?
What colour is dad’s hair?
Cross: Mom = hhcc x Dad = HhCC
Possible hair colours of offspring are brown and regular blond.
Dad’s hair is Brown.
gametes
Dad HC hC
Hannah hc
F HhCc
F1 hhCc