Question

In gerbils, the gene that specifies coat color is sex‑linked and has multiple alleles, as follows: B ‑ black, br ‑ brown, by ‑ yellow, and b ‑ albino. The allele br is incompletely dominant over by, the combination br by giving tan color; otherwise, dominance is in the order given ‑‑ B, br, by, b. (For your information, gerbils are mammals.) A black gerbil mated with a yellow gerbil gave one brown male and one black female offspring.

a. What is the sex of the black parent?

b. What is the genotype of the brown offspring?

c. If the two offspring were to mate with each other, what is the probability that they will have a yellow offspring?

d. If the two offspring were to mate with each other, what is the probability that the first three female offspring will be black?

e. If the brown offspring were to mate with his mother, what is the probability that the first two offspring will be brown males?

Answer 1

Answer:

B—br—by—b

a). The sex of the black parent is female

Explanation:

X=X-chromosome

Y-chromosomes

Black-female (XB Xbr) x Yellow ( Xby Y)---Parents

	Xby	Y
XB	XB Xby (black female)	XBY (black male)
Xbr	Xbr Xby (brown female)	Xbr Y (brown male)

b). Brown offspring genotype = Xbr Y (brown male)

c). ¼ or 25% of the children will be yellow.

Explanation:

XB Xby (black female) x (brown male) Xbr Y ----Parents

	Xbr	Y
XB	XB Xbr (black female)	XBY (black male)
Xby	Xbr Xby (brown female)	Xby Y (yellow male)

d).

The probability of black female = ¼

The probability that the first three female offspring will be black=¼*¼*¼= 1/64

e). Xbr Y (brown male) x Black female (mother) XB Xbr

	Xbr	Y
XB	XB Xbr (black female)	XBY (black male)
Xbr	Xbr Xbr (brown female)	Xbr Y (brown male)

The probability of brown male = ¼

the probability that the first two offspring will be brown males= ¼ * ¼ = 1/16