Question

Human hair color is controlled by one gene with four alleles (with some incomplete dominance):

HBr = brown
HBd = blonde
hR = red
hbk = black
The possible genotypes and phenotypes:
HBd HBd or HBd hbk = blonde
HBr HBr or HBr hbk = brown
HBd HBr = mousy brown
HBr hR = auburn
HBd hR = strawberry blonde
hRhR or hRhbk = red
hbk hbk = black

If someone with strawberry blonde hair has a child with someone who has mousy blonde hair, what are the genotype and phenotype probabilities of their children?

If someone with brown hair (with a red hair parent) has a child with someone who has blonde hair (who also has a parent with red hair), what are the genotype and phenotype probabilities of their children?

Answer 1

• If someone with strawberry blonde hair (HBd hR) has a child with someone who has mousy blonde hair (HBd HBr), the genotype probabilities of their children would be:

25% chance of HBd HBd (blonde)

25% chance of HBd hR (strawberry blonde)

25% chance of HBd HBr (mousy blonde)

25% chance of HBr hR (auburn)

The phenotype probabilities would be:

50% chance of blonde

25% chance of strawberry blonde

25% chance of auburn

• If someone with brown hair (HBr HBr or HBr hR) has a child with someone who has blonde hair (HBd HBd or HBd hR) who also has a parent with red hair. The genotype probabilities of their children would be:

25% chance of HBr HBr (brown)

25% chance of HBr HBd (mousy blonde)

25% chance of HBr hR (auburn)

25% chance of HBd hR (strawberry blonde)

The phenotype probabilities would be:

25% chance of brown

25% chance of mousy blonde

25% chance of auburn

25% chance of strawberry blonde

Keep in mind that there are also incomplete dominance and environmental factors that can affect hair color, so these probabilities may not be exact.