Question

In________both dominant and recessive alleles lack their dominant and recessive relationships.
A. Incomplete dominance
B. Polygenic inheritance
C. Multiple alleles
D. Codominance

Answer 1

Hint: In human DNA, each gene may exist in alternative forms known as alleles, which code for different varieties of an inherited character. A dominant allele conceals the expression of a recessive allele. A recessive allele exerts its effect only in the homozygous state and not in heterozygous condition.

Complete answer:
Alleles are the genes occupying corresponding positions on homologous chromosomes and controlling the same characteristic (height) but producing different effects (tall or short).

Alleles can be of different types and their expression can vary.
• Wild type alleles- These are prevalent in a population. They encode for proteins.
• Mutant alleles- The alleles that are present in less than 1% amount in a population and have been altered by mutation.
•Dominant alleles- These mask the expression of recessive alleles and are usually denoted by an uppercase letter.
• Recessive alleles- These express only in the homozygous state.

The dominant gene overpowers the recessive gene, but sometimes codominance can occur. It happens when alleles are lacking dominant and recessive relationships, and are both observed phenotypically to the same degree. The phenotypic effect of each allele is observable in the heterozygous condition. The heterozygous genotype gives rise to a phenotype distinctly different from either of the homozygous genotypes.
Example- The alleles governing the M-N blood group in humans are examples of codominant alleles.

Hence, the correct answer is option (D).

Note: Incomplete dominance is a condition when neither allele is dominant over the other.
For example- When a red-flowered plant is crossed over with a white-colored flower, a pink-colored flower is obtained.
• Polygenic inheritance refers to multiple gene inheritance.
For example- Height is not only controlled by one gene but a number of genes are responsible.
• Multiple alleles: When more than two different forms of a given gene exists in a species,
For example- ABO blood group system.