Genotype versus phenotype
An organism's genotype is
the set of genes that it carries. An organism's phenotype is all of its observable characteristics which are influenced both
by its genotype and by the environment. So in defining evolution, we are really concerned
with changes in the genotypes that make up a population from generation to generation. However, since an
organism's genotype generally affects its phenotype, the phenotypes that make up the
population are also likely to change.
For example, differences in the genotypes can produce different phenotypes. In these house
cats, the genes for ear form are different, causing one of these cats to have normal ears and
the other to have curled ears.
A change in the environment also can affect the phenotype. Although we often
think of flamingos as being pink, pinkness is not encoded into their genotype. The food they
eat makes their phenotype white or pink.