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11 June, 08:08

Sickle cell anemia is a recessive trait in humans. In a cross between a father who has sickle cell anemia and a mother who is heterozygous for the gene, what is the probability that their first three children will have the normal phenotype

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  1. 11 June, 12:04
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    1/8

    Explanation:

    Assuming the allele for sickle cell is represented by s, the alternate non-sickling allele will be S.

    A ss father marries a mother that is heterozygous for the trait:

    ss x Ss = Ss, Ss, ss and ss.

    Thus, 50% of their children will be heterozygous normal for the trait while 50% will be homozygous recessive (affected) for the trait.

    The probability of producing normal children is 1/2. Hence, the probability of their first three children having a normal phenotype is equivalent to the probability of the first being normal, the second being normal and the third being normal. Mathematically;

    = 1/2 x 1/2 1/2 = 1/8

    The probability that their first three children will have the normal phenotype is 1/8.
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