Albinism is an autosomal recessive trait. A normally pigmented man marries an al

Question

Albinism is an autosomal recessive trait. A normally pigmented man marries an albino woman. If their first child was an albino what would their (the parents) genotypes and their child's genotype be? If they have more children what other genotypes could there be? An albino man marries normally pigmented woman. They have 13 children all of whom are normally pigmented. What are the probable genotypes of the children and parents? A normally pigmented marries an albino woman. The man's father was an albino. The woman's parents were both normally pigmented. The man and woman have three children, two normally pigmented and one albino. List each of these persons and give their probable genotypes. In Drosophila, the fruit fly, wild type long wings "G" is dominant over vestigial wing (g).

Explanation / Answer

6. In the case of autosomal recessive trait, the disease occur when both recessive allele is present in single individual. Here, assume the gene for pigmentation is A, dominant and a, recessive. Normal pigmented male can have two possible genotype homozygous AA or heterozygous Aa whereas albinism women have only recessive genotype aa. In autosomal recessive trait, when unaffected individual mate with affected people, all children produced are unaffected but in this situation one child is affected means unaffected individual is heterozygous.

Parent male Aa genotype

Parent female aa genotype

First child = aa genotype

Aa X aa

Aa Aa aa aa children genotype

Here, half chidren has heterozygous genotype means normal pigmentation and half of the children has homozygous recessive genotype means albinism.

7. As mentioned previously when affected individual mate with unaffected individual (homozygous), then all children produced are unaffected means have normal pigmentation. Albinism occur in the presence of both recessive allele aa.

So, Female genotype = AA

Male genotype = aa

AA X aa

Aa Aa Aa Aa chidren genotype

All chidren produced have heterozygous genotype for pigmentation, therefore, all are unaffected with normal pigmentation.

8. First consider a normal pigmented male from albinism father, means man father has genotype aa

Man mother can have genotype either Aa or AA, but here male is normally pigmented because his mother has homozygous genotype AA. In case of heterozygous there could a be a chance of affected male. So, the male has heterozygous genotype Aa.

Man genotype = Aa

Man father genotype = aa

Man mother genotype = AA

This man marries a albino women whose genotype is aa, woman have both parent normally pigmented means heterozygous genotype, only this genotype can give affected children.

Albino women genotype aa

Parents genotype (both male and female) = Aa

Normally pigmented man marries a albinism women

Aa X aa

Aa Aa aa aa

They have 3 children, 2 are unaffected with Aa genotype and one is affected with aa genoype.

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