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Principles of Inheritance and Variation
Gamete Formation and Independent Assortment
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Concepts tested
- Probability of a gamete type
All Questions
2004 AIPMT 1 question
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A male human is heterozygous for autosomal genes A and B and is also hemizygous for hemophilic gene h. What proportion of his sperms will be abh :-Genotype of the man: Aa Bb $X^hY$ (heterozygous for A and B, and hemizygous for h, i.e. one $X^h$ and a Y).
Assuming independent assortment, each gene pair separates independently into the sperms.
Probability of a sperm getting a $= \dfrac{1}{2}$ (A or a)
Probability of getting b $= \dfrac{1}{2}$ (B or b)
Probability of getting the X with h $= \dfrac{1}{2}$ (the other half of the sperms carry Y)
Probability of an abh sperm $= \dfrac{1}{2} \times \dfrac{1}{2} \times \dfrac{1}{2} = \dfrac{1}{8}$
The man forms $2^3 = 8$ types of sperms in equal proportions (ABh, ABY, Abh, AbY, aBh, aBY, abh and abY), and abh is one of them.
So $\dfrac{1}{8}$ of his sperms will be abh.