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question 33
imagine that we mate two black labrador dogs with normal vision and find that three of the puppies are like the parents, but one puppy is yellow with normal vision and another is black with pra (progressive retinal atrophy, a serious disease of vision). we can conclude that

1. both of the parents are homozygous for both traits.
2. the same alleles that control coat color can also cause pra.
3. the alleles for color and vision segregate independently during gamete formation
4. the alleles for color and vision segregate dependently during gamete formation.

Explanation:

• For option 1: If parents were homozygous for both traits, all puppies would be like parents. But we have different - colored and - vision puppies, so this is wrong.
• For option 2: There is no indication that the alleles for coat color cause PRA. These are two different traits.
• For option 3: According to Mendel's law of independent assortment, alleles for different traits (color and vision here) segregate independently during gamete formation. This explains the variety of puppies (different color and vision combinations).
• For option 4: If they segregated dependently, we would not see the new combinations (e.g., yellow with normal vision and black with PRA) as easily as we do.

Answer:

1. the alleles for color and vision segregate independently during gamete formation