The frequency of the Xlinked recessive allele c responsible

The frequency of the X-linked recessive allele (c) responsible for color-blindness is 0.10, and the normal allele (C) is at a frequency of 0.90 in a random mating population. A color-blind woman marries a man with normal vision from this population. What is the probability that their first daughter will be color-blind? (2 points)

Solution

Mother\'s genotype (color blind) X^c X^c

Father\'s genotype (normal vision) X^C Y

X^C Y

X^C X^c

X^c Y

X^C X^c

X^c Y

X^c

X^c

From the Punnett square, it is clear that all the girls remain with normal vision but carrier because of their heterozygous condition.

X^C X^c       [normal (carrier) girl]

X^c Y

[Color blind boy]

X^C X^c

[normal (carrier) girl]

X^c Y

[Color blind boy]

In terms of frequency and probability;

frequency of color-blindness recessive allele (c) = 0.10

frequency of normal allele (C) = 0.90

By using, allele distribution, p² + 2pq + q² = 1

probability of two carriers or their first daughter will be color-blind = 2pq

                                                                                           = 2 (0.10) (0.90)

                                                                                        = 0.18