In the mouse, gene A allows pigmentation to be deposited in the individual coat hairs; its allele a prevents such deposition of
pigment, resulting in an albino. Gene B gives agouti (wild-type fur); its allele b gives black fur. What would the expected ratio of the progeny be in a cross of a doubly heterozygous agouti mouse mated with a doubly homozygous recessive white mouse?
Explanation: In a dihybrid cross, an organism with two different characteristics crosses with another organism with other two different characteristics. In this question, for example, the doubly heterozygous agouti mouse is represented by AaBb and the doubly homozygous recessive white mouse is aabb. So crossing them, we'll have
ab
AB AaBb (agouti)
Ab Aabb (black fur)
aB aaBb (albino)
ab aabb (albino)
Analising the table, there is 1 in 4 chances of a agouti; 1 in 4 chances of a black fur and 1 in 2 chances of an albino, therefore, the ratio is 1:2:1.
