Question

Coorect Answer please

In cats a sex (X) linked pair of alleles, Bb, determines color of the fur. The allele B for yellow is incompletely dominant over b for black so that Bb individuals are tortoise shell, a splotchy mixture of yellow and black hairs.

A) A yellow male is crossed with a tortoise shell female. If the female has a litter of 6 males, what phenotypes might they express?

B) A yellow cat has a litter of 2 tortoise shell and 1 yellow. What is the probable sex of the yellow kitten.

C) A tortoise shell female has a litter of 7; 2 yellow females, 2 tortoise shell females, 1 black and 2 yellow males. What was the probable genotype and phenotype of the father?

D) Tortoise shell cats that are identical twins are very unlikely to have the same splotchy mixture of yellow and black hairs. What is the genetic explanation for this?

Answer 1

A) yellow male is X^B Y and female is X^BX^b, there are 6 males

	XB	Y
XB	XBXB	XBY (yellow male)
Xb	XBXb	XbY (black)

B) cat is yellow and it has 2 tortoise shell and 1 yellow kitten X chromosome to males are passed by mother, since the mother is yellow she is X^BX^B she can pass X^B to her male offspring,so yellow kitten has to be male, only females can be tortoiseshell because the female can only be heterozygous for B locus that is X^BX^b tortoiseshell kitten means their father is black, because mother is yellow she passes X^B and father passes X^b .

C) tortoiseshell female has a litter of 7; 2 yellow females, 2 tortoiseshell females, 1 black and 2 yellow males.

female is

X^BX^b - tortoiseshell female, in the kitten there are 2 females this shows both father and mother have passed allele X^B so the father has be X^BY

	XB	Xb
XB	XBXB ( yellow female)	XBXb ( tortoiseshell female)
Y	XBY (yellow male)	XbY ( black male)

so the genotype and phenotype of the father are X^BY and yellow respectively.

D) females who are heterozygotes X^BX^b usually have tortoiseshell this happens due to the random X chromosome inactivation which occurs during early embryonic stages that is one X chromosome is inactivated in the cell, inactivated X chromosome can be either paternal or maternal so 2 different cells can have X^B in an inactive state or X^b in the inactive state cells arise from those embryonic cells will also have same X chromosome inactivated so it leads to random spots, so two identical twins cannot have same spots because of random X chromosome inactivation.