In a two-point test-cross analysis,a dihybrid F₁ fly is crossed to a
A)pure-breeding mate with a dominant phenotype (AABB).
B)pure-breeding mate with a recessive phenotype (aabb).
C)heterozygote mate (AaBb).
D)mate that is dominant for one gene and recessive for the other (AAbb or aaBB).
E)second dihybrid F₁ fly (sibling cross).

Question

Quizplus · Accepted Answer

The best choice for a two-point test-cross analysis is to cross the dihybrid F₁ fly with a pure-breeding mate with a recessive phenotype (aabb). This allows for the observation of independent assortment of the two genes being tested, as all offspring will show the phenotype corresponding to the dominant allele in the dihybrid F₁ fly. If a heterozygote mate (AaBb) or a mate that is dominant for one gene and recessive for the other (AAbb or aaBB) were used, the observed phenotypic ratios would not allow for the determination of independent assortment, as some offspring would show the recessive phenotypes for one or both genes. A sibling cross (choice E) would also not be ideal, as it would not allow for the observation of the segregation of the two genes being tested.

In a Two-Point Test-Cross Analysis,a Dihybrid F₁ Fly Is Crossed