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Based on the information given, the best option to explain this scenario is C: Both parents are heterozygous for the gene for dimples.
In genetics, dimples are considered a dominant trait. This means that if an individual inherits even one copy of the gene for dimples, they will express the trait. Let's analyze the options:
A: Only one parent is homozygous dominant.
If only one parent is homozygous dominant (DD), then all their offspring would have dimples. This option does not explain why neither of the children has dimples.
B: One of the parents has a genetic mutation against the gene for dimples.
A genetic mutation against the gene for dimples would result in the absence of dimples in the individual who has the mutation. However, if both parents have dimples, it is highly unlikely that one of them has a genetic mutation against the gene for dimples. Therefore, this option is not the best explanation.
C: Both parents are heterozygous for the gene for dimples.
If both parents are heterozygous (Dd) for the gene for dimples, there is a 25% chance that their children will inherit two copies of the recessive allele (dd) and not have dimples. This option is the best explanation for why neither of the children has dimples, even though both parents have the trait.
D: Both parents are homozygous dominant for the gene for dimples.
If both parents are homozygous dominant (DD) for the gene for dimples, then all their offspring would have dimples. This option does not explain why neither of the children has dimples.
Therefore, option C, both parents being heterozygous for the gene for dimples, is the best explanation for this scenario.
~ Sun
