Question

Which genetic mutation will result in a change in phenotype expression?

A. a mutation in a body cell that is dominant for the trait
B. a mutation in a body cell that is heterozygous for the trait
C. a mutation in a body cell that is homozygous for the trait
D. a mutation occurring in any muscle or skin cell

Answer 1

i think its B as in hetrozygous corss u can see variation in phenotype

Answer 2

Many mutations occurring in muscle or skin cells can be silent if they happen in regions of the genome that are not relevant for the normal cell function (non-coding DNA, genes that encode proteins specific to a different cell type, etc.), so it cannot be D.

A homozygous cell is a polyploid cell with equal alleles at the same position in consideration (locus) in all its chromosomes. Depending on the mutation, it could go unnoticed if the affected functions can be taken up by the remaining intact copies of the gene, so the response cannot be C.

A heterozygous cell is a polyploid cell with different alleles at the same locus in all its chromosomes, and, again, a mutation in one of them could go unnoticed if the other alleles can take up its function. Response B cannot be correct.

However, a dominant allele for a trait implies that its function cannot be taken up by the remaining copies of the gene; that is why it is called "dominant", because its expression masks the expression of the recessive counterparts. A mutation in a dominant allele will always go noticed because it will allow the expression of the recessive allele (assuming diploidicity), silent while the dominant allele was functional. I might be wrong, but I would say A is correct.