In humans, albinism occurs when there is a deficiency of melanin. It is caused by a recessive allele

skin-pigmentation
scenarios

#1

A) In humans, albinism occurs when there is a deficiency of melanin. It is caused by a recessive allele (a). People that get at least one copy of the dominant allele (A) will have normal skin pigmentation. In the following scenarios, what are the probable genotypes of the father, mother, and children?

  1. Both parents have normal skin color. They have four children, one of which is albino, and the other three have normal skin color.

  2. Both parents and all children are albinos.

  3. The mother has normal skin color, but the father is albino. They have four children. Two of the children have normal skin color, and two of the children are albinos.

  4. The mother is albino, but the father has normal skin color. They have four children, and all of them have normal skin color.

Answer:

1. Parents will both be heterozygous for the allele (Aa). This would result in 75% chance that the offspring has normal skin pigmentation and 25% chance that offspring is albino. Children are either AA, Aa, or aa.
2. Parents will both be homozygous recessive for the allele (aa). All offspring will be albino as well, with the genotype aa.
3. The mother will be heterozygous (Aa) and the father will be homozygous recessive (aa). This results in a 50/50 split whether the offspring is albino or normal, with a genotype of either Aa, or aa.
4. The mother will be homozygous recessive (aa) and the father will be homozygous dominant (AA). This results in all offspring being heterozygous, with genotypes of aa.