Question

Two heterozygous black cats mate.

a) What is the probability that, if the litter has size 2, the kittens will be born in the order white-black?

b) What is the probability that, if the litter has size 2, it will contain 1 black kitten and 1 white kitten?

Answer 1

Let the genotype of the heterozygous cat be Bb.

where B corresponds to black colour and is dominant while b corresponds to white colour and is recessive.

Mating:

	B	b
B	BB (Black)	Bb (Black)
b	Bb (Black)	bb (White

i.e probability of black colour is 0.75 (3/4) while of white colour is 0.25 (1/4)

A.

If litter size is 2, the sample space of occurrence of colour among offsprings will be:

P(WB) = 0.25*0.75

= 0.1875

B.

One black and one white = BW or WB

P(BW or WB) = P(WB) + P(BW)

= 0.25*0.75 + 0.75*0.25

= 0.1875 + 0.1875

= 0.375

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