Complete each statement below to demonstrate an understanding of incomplete domi

Question

Complete each statement below to demonstrate an understanding of incomplete dominance.

When a heterozygote has an intermediate phenotype between that of either homozygote,  ____________  is said to be exhibited.

For example, a plant called a four-o'clock can be red or white, and the intermediate heterozygote offspring produced by a mating of the two exhibits the color  ____________ .

This is not a  ____________  of the traits, since offspring of the pink flower can be red, white, or pink.

The reappearance of the three phenotypes makes it clear that there is a  ____________  pair of alleles involved.

This type of inheritance is in contrast with  ____________ , where alleles that display true dominant/recessive inheritance have dominant alleles that are not always expressed.

In these cases, it is thought that  ____________  factors could play a role in the expression of the gene, preventing dominant genotypes from expressing dominant phenotypes

Explanation / Answer

When a heterozygote has an intermediate phenotype between that of either homozygote,  incomplete dominance is said to be exhibited.

For example, a plant called a four-o'clock can be red or white, and the intermediate heterozygote offspring produced by a mating of the two exhibits the color  pink.

This is not a  blending of the traits, since offspring of the pink flower can be red, white, or pink.

The reappearance of the three phenotypes makes it clear that there is a  single pair of alleles involved.

This type of inheritance is in contrast with incomplete penetrance , where alleles that display true dominant/recessive inheritance have dominant alleles that are not always expressed.

In these cases, it is thought that  environmental factors could play a role in the expression of the gene, preventing dominant genotypes from expressing dominant phenotypes.

Explanation:

Incomplete dominance is exhibited when the heterozygote has an intermediate phenotype between that of either homozygote due to combined allele expression (In this example of four o clock flowers red + white giving rise to pink color). One more example which can be cited is familial hypercholesterolemia. Heterozygotes witha single copy of the gene have a lesser degree of symptoms when compared to homozygous dominant. It is not a result of blending of traits because the offspring can be red, white or pink. Reappearance of three phenotypes indicates that only single pair of alleles is involved.

In contrast to incomplete dominance, incomplete penetrance, is when alleles that display true dominant or recessive inheritance have dominant alleles which are not always expressed. It is due to the environmental factors which affect the gene expression, preventing dominant genotypes from expressing dominant phenotypes. The dominant allele do not always signify the phenotype. Example is Hereditary spherocytosis

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