What statement is true about lethal alleles? a. they cannot be maintained in a gene pool because they are always dominant. b. they cannot be maintained in a gene pool because the individuals with them never survive. c. they can be maintained in a gene pool if they are expressed before reproductive age. d. they can be maintained in a gene pool by heterozygous carriers.

Hello!

If you were to infer that non-lethal alleles are dominant, and lethal alleles are recessive, then let's assign A as the dominant allele, and a as the recessive allele.

Dominant homozygous (AA) or heterozygous (Aa) individual are not affected by the lethality of this allele because dominant alleles (A) are... dominant!

You are affected by the lethal alleles if and only if you are homozygous (aa) recessive.

So, if you were heterozygous (Aa), you wouldn't be affected by the lethal gene, because you have the dominant allele (A), but the recessive allele (a) would be in the next generation's gene pool.

Therefore, the answer is choice D, they can be maintained in a gene pool by heterozygous carriers.