is it true that dominant phenotypes are always the most common in a population? explain?

Answer 1

Not always. If there is a selective reason for the recessive trait, then the recessive phenotype will be more common. But if there is no selective pressures, then AA, Aa, aA will all show the dominant type, while only aa will show the recessive trait. So 3/4 will so dominant while 1/4 will show recessive trait.

Answer 2

This all depends on the percentage of the dominant and recessive alleles in the gene pool. For instance, in the United States Type O blood is the most common, even though the O allele is recessive to A and B.

If there are far more O alleles in the gene pool than A and B alleles, then the people have a greater chance of having Type O blood.