Apopulation of red squirrelfish breeds and produce offspring, 75% are still red but 25% are yellow. this variation in the color of the squirrelfish can be explained by what?

Dominant nature of allele for the red skin coat that masks the yellow allele present in the heterozygous parent red squirrelfish.

Explanation:

A dominant allele for a gene is the one that is expressed in both homozygous and heterozygous genotypes. The expression of a recessive allele of a gene is masked by the presence of the dominant allele in the heterozygous genotype.

The parent red squirrelfish produce progeny in 3 red: 1 yellow phenotype ratio. This indicates that the parent red squirrelfish is heterozygous for skin coat color and the allele for red color is dominant over the allele for yellow color. If the allele for red color is "R" and the one for yellow color is "r" , the genotype of parent red squirrelfish would be Rr. A cross between Rr x Rr would give 3 red (1 RR and 2 Rr) and 1 yellow (1 rr) progeny.