Question

In guinea pigs, black coat colour (G) dominates over white (g) and brown eyes (B) dominate over blue (b). The alleles for coat colour and eye colour are not linked. What will be the probability of the offspring having blue eyes and a white coat if both parents are heterozygous for eye and coat colour? Find the probability using a Punnett square.

Answer 1

The BbGg male is crossed with a BbGg female, which are both heterozygous for both the characters for eye and coat colour.

	BG	Bg	bG	bg
BG	BBGG	BBGg	BbGG	BbGg
Bg	BBGg	BBgg	BbGg	Bbgg
bG	BbGG	BbGg	bbGG	bbGg
bg	BbGg	Bbgg	bbGg	bbgg

Only bbgg gives blue eyes and a white coat.

There is one bbgg out of 16 total combinations.

Probability calculation:

P[white coat (gg)] = `1/4`

P[blue eyes (bb)] = `1/4`

Since genes are unlinked, probabilities multiply:

P(bbgg) = `1/4 xx 1/4`

= `1/16`

∴ `1/16` or a 6.25% chance of blue eyes and a white coat.