Question

Consider the following three point cross: ABC/abc x abc/abc. Which of the following is not a possible genotype? (Consider both recombinant and nonrecombinant progeny)

1) ABC/abc
2) aBC/abc
3) ABC/ABC
4) AbC/abc
5) abc/abc

Answer 1

In a three-point cross, genotypes represent possible combinations resulting from recombination. Among the given options, the genotype ABC/ABC is not possible due to the presence of both dominant and recessive alleles. The other options represent possible combinations with or without recombination.

Step-by-step explanation:

In a three-point cross, we consider three genes on different chromosomes. The given cross ABC/abc x abc/abc represents a cross between true-breeding flies with genotypes AABBCC and aabbcc. By considering the possible recombinations, we can determine which genotype is not possible.

1. ABC/abc - This is a possible genotype since there is no recombination.
2. aBC/abc - This is a possible genotype as it occurs when there is a recombination between alleles B and C.
3. ABC/ABC - This is not a possible genotype as it implies no recombination and the presence of both dominant and recessive alleles, which contradicts the true-breeding nature of the parental flies.
4. AbC/abc - This is a possible genotype as it occurs when there is a recombination between alleles A and C.
5. abc/abc - This is a possible genotype since there is no recombination.