Mice from wild populations typically have gray-brown (or agouti) fur, but in one
ID: 150454 • Letter: M
Question
Mice from wild populations typically have gray-brown (or agouti) fur, but in one laboratory strain, some of the mice have off-white fur. A single off-white male is mated to several agouti females and 40 progeny are produced; 22 with agouti fur and 18 with off-white fur. The Fi agouti animals are then intercrossed with each other to produce an F2 generation, all of which are agouti. Similarly, the Fi off-white animals are intercrossed with each other, but their F2 progeny segregate into two classes; 18 are agouti, and 52 are off-white. Subsequent crosses between off-white F2 animals also segregate off-white and agouti progeny. (For symbols, use a letter that represents the dominant phenotype, uppercase for dominant, lowercase for recessive.) 4.Explanation / Answer
Ans. (a) These results are possible because of embryonic lethality and incomplete dominance. Agouti is the wild type and homozygous for gene A. Gene A is mutated and formed another allele 'a'. Allele 'a' is lethal in its homozygous condition. So individuals with aa can never be formed. Allele 'A' is incompletely dominant over 'a'. This gives different phenotype for Aa, which is off-white.