Question

In raccoons, a dark face mask is dominant over a bleached face mask. Several crosses were made between raccoons that were homozygous for a dark face mask and that were homozygous or bleached face masks. What percentage of the offspring would be expected to have a dark face mask?
A. 0%
B. 50%
C. 75%
D. 100%

Answer 1

Racoons are mid sized mammals. Here in the question given dark face mask (DD) is dominant over bleached face mask (dd) that means it is based on dominant-recessive relationship. Dominant characters are able to express themselves either in homozygous and heterozygous conditions. Whereas recessiveness is able to express only in heterozygous condition.

Complete answer:
Dark face mask and bleached face mask represent the parental generation in which dark face mask is homozygous dominant character whereas bleached face mask is homozygous recessive character.

Let suppose dark face mask is represented as 'DD' as it shows dominance over bleached face mask and bleached face mask represented as 'dd' as it shows recessive over dark face mask. In diploid organisms, therefore such a pair of characters (expressions) would present. If a cross was made between two true-bred (homozygous) parents, each parent would have two similar unit factors. The true breeding dark face mask has two unit factors or alleles (DD) and the true breeding bleached face will possess two similar unit factors (dd).
When DD crossed with dd the resultant will be Dd and it shows only the dominant character i.e. dark task mask. This is because the dominant character expresses itself in either homozygous or heterozygous condition. So the percentage of offspring showing a dark face mask is 100% and a bleached face mask is 0% after crossing.

Hence, the correct answer is option (D).

Note: Dominant- recessive relationship within the allelic pair- one allele’s being dominant suppresses the effect of another of the pair. This shows that through recessive character is not expressed in F1 hybrid; it is expressed phenotypically in F2. Hence the cross between dark and bleached face mask is resulted in 100% heterozygous dark face mask offspring.