In carrier pigeons there is a rare inherited condition that causes the death of the chicks before hatching. In order for this disease to be passed from generation to generation there must be parent birds that:.
1.are heterozygous for the disease.
2. have the disease themselves.

1. are heterozygous for the disease.

Explanation:

Since the disease causes the death of chicks before hatching, it means that those with the disease cannot be found in the population. In order for the allele of the disease to be passed from generation to generation, there must be parent birds that are carrying the disease in heterozygous state.

Option 1 is the correct option.

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