Correct option is C
The most likely combination of parental genotypes in this case is Aa and aa. Here's why:
- In the offspring, we know there are 500 'aa' individuals and 500 individuals of the other genotypes (AA and Aa). Since aa is the homozygous recessive genotype, it can only be produced if both parents contribute the recessive allele (a).
- If one parent is Aa (heterozygous), they can pass on either A or a. If the other parent is aa (homozygous recessive), they can only pass on a. Therefore, the potential offspring genotypes from this combination would be:
- Aa (from A from the heterozygous parent and a from the homozygous parent)
- aa (from a from both parents)
- This combination will produce offspring in a 1:1 ratio of Aa and aa, which matches the given numbers: 500 aa offspring and 500 Aa offspring.
Information Booster:
- In a Aa x aa cross, the expected offspring genotypes are:
- Aa (heterozygous): 50% probability
- aa (homozygous recessive): 50% probability
This matches the observed ratio of 500 aa and 500 of the other genotypes (mostly Aa).
Additional Information:
- Aa and Aa: This combination would result in a 1:2:1 ratio of AA, Aa, and aa genotypes, so it would produce more than 500 aa offspring (about 250) and would not fit the ratio required by the problem.
- AA and Aa: This combination would produce only AA and Aa offspring, with no aa offspring, which does not match the given numbers.
- AA and aa: This cross would only produce Aa offspring, and since there are no aa offspring, this combination is not correct.
