Question

A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation?

a. about 66%

b. 25%

c. 50%

d.75%

Answer 1

The correct option is d (75 %)

In the present question, white color of tiger is due to a recessive allele. Suppose the gene responsible for pigmentation is "A", which can be present as:

AA: Homozygous dominant (will express as normal pigmentation)

Aa: Heterozygous dominant (Will also express as normal pigmentation)

aa: Homozygous recessive (Will express as white color as the allele responsible is recessive)

If Two normal pigmented tigers are mated and produces white tiger, they must be heterozygous dominant. Let us see how:

                                   Aa x Aa     ................... P

	A	a
A	AA Normal pigmented 25 %	Aa Normal Pigmented 25 %
a	Aa Normal Pigmented 25 %	aa White colored 25 %

From the punnett square shown above it is clear that

25% of the offsprings will be white colored

75 % (25% AA and 50 % Aa) will be normal pigmented.

Option a is incorrect: 66 % will never be obtained in populations following mendelian inheritance.

Option b and c are incorrect: 25 % offsprings will be AA and 50 % offsprings will be Aa. hence a total percentage of normal pigmented offsprings will be 75 % (25 % + 50 %).