Imagine that beak color in a finch species is controlled by a single gene. You mate a finch homozygous for orange (pigmented) be
ak with a finch homozygous for ivory (unpigmented) beak and get numerous offspring, all of which have a pale, ivory-orange beak. This pattern of color expression is most likely to be an example of A) incomplete dominance.
B) codominance.
C) pleiotropy.
D) polygenic inheritance.
It is a clear case of incomplete dominance. This kind of inheritance shows deviation from Mendel's popular law of genetics which is known as "Law of Dominance". This law states that when two pure breeding parents i.e. homozygous dominant and homozygous recessive are mated then all their off-springs are genotypically heterozygous but phenotypically they all show dominant trait. But in incomplete dominance, <u>the dominant allele is unable to mask the expression of recessive allele completely</u> which leads to a phenotype which is a blend of both the traits.
In the example, orange beak is unable to mask the expression of ivory beak completely as a result of which all the off-springs have an intermediate trait which is pale, ivory-orange beak.
