162k views
5 votes
A specific X-linked recessive allele is lethal. Males that inherit the recessive allele and females that are homozygous recessive will abort before birth. What is the probability that a heterozygous mother will give birth to a child with only one copy of the recessive allele?

User ElArbi
by
8.3k points

1 Answer

3 votes

Answer:

The probability that a heterozygous mother will give birth to a child with only one copy of the recessive allele is
(1)/(3)

Explanation:

Let the recessive allele causing lethal disease be represented by "r"

Let the dominant allele causing no lethal disease be represented by "R"

Genotype of heterozygous mother will be
X_RX_r

Genotype of heterozygous mother will be
X_rY

A cross between
X_RX_r and
X_rY will produce following offspring


X_RX_r


X_RY


X_rX_r


X_rY

Thus, out of four offspring only child with genotype
X_rY will die

Thus, only three offspring remain alive and out of these three only one child with genotype
X_RX_r has one copy of recessive allele.

Thus, the probability that a heterozygous mother will give birth to a child with only one copy of the recessive allele is
(1)/(3)

User OctaveL
by
8.3k points