Question

What are the phenotypes for YY, Yy, yy. Where Yellow (Y) hair is dominant to blue (y)?

Answer 1

Well simply knowing that yellow hair colour is dominant to blue, Yellow Y hair allele will produce the functioning protein or pigment to product the yellow colour whereas the blue colour is only produced if both recessive alleles are present.

YY = yellow
Yy = Yellow
yy = blue

Answer 2

Phenotype indicates outward appearance. When an allele has a dominant trait, the phenotype will always exhibit that dominant trait, therefore:

YY = Yellow hair
Yy = Yellow hair
yy = Blue hair