Question

In rabbits, brown coat (B) is dominant to white coat (b). A rabbit breeder wants to know the genotype of his best looking male brown rabbit using a test cross. He has brown females and white females available to conduct his breeding experiments.

Required:
a. What should be the coat color of the female he must use in this test cross?
b. If the test cross produces seven (7) brown rabbits and one (1) white rabbit, what is the genotype of the brown male rabbit?

Answer 1

a. white

b. Bb

Step-by-step explanation:

A test cross usually involve crossing an individual whose zygosity is unknown with a homozygous recessive version of individual of the same species.

Brown coat (B) is dominant over white coat (b). Hence, there is no way to physically distinguish between a BB rabbit and a Bb rabbit because both of them will be brown. A bb rabbit however will be white in appearance.

A test cross would therefore involve crossing the brown male rabbit with bb (white) rabbit.

Assuming that the genotype of the brown rabbit is BB, all the progeny will be brown as shown by the cross below.

BB x bb

Bb Bb Bb Bb

In order word, assuming the genotype is Bb, some of the offspring will appear brown while some will appear white.

Bb x bb

Bb Bb bb bb

Hence, the only way the test cross would produce white offspring is if the genotype of the brown rabbit is heterozygous, Bb.