Question

In mice, black is dominant to white color and color is determined by a single gene. Two black mice are crossed. They produce 2 black offspring and one white offspring. If the white offspring is crossed with one of its parents, what percent of the offspring are expected to be white?

Answer 1

Answer:

50%

Explanation:

If black is dominant to white color and crossing with parents produced some progeny which were black and a white progeny then it simply indicates that parents were heterozygous for the trait even if phenotypically they appeared black. A cross between parents is shown as under:

                              Parents

                              Bb x Bb

Progeny:      BB      Bb     Bb     bb

BB and Bb allelic combinations produced a black mice while bb combinations produced white mice.

Now the subsequent cross between one of the parents and white off spring is shown as under:

                               Bb x bb

Progeny:         Bb    Bb    bb    bb

It is clear from the cross above that the progeny with Bb allelic combinations will be black while with bb combinations they will be white. 2 out of the 4 progeny are genotypically bb that means they are white i.e. 50% progeny are white.

Answer 2

Answer:

50%.

Explanation:

Mendel is known as the father of genetics. He explained the laws of genetics including the law of segregation, law of independent assortment and concept of dominance.

The mice has black as dominant color. The parents are heterozygous as there cross yield a white recessive progeny. The cross between white offspring and one of its parents is as follows:

Parents : Bb    ×           bb

Progeny :  Bb, Bb ( Black ) and bb, bb (white).

Thus, the white offspring are 50%.