Question

In an Organism, mutation in a single gene exhibits multiple phenotypic expressions. Identify the underlying genetic mechanism in the above instance.

• A. Polygenic inheritance
• B. Multiple allelism
• C. Pleiotropy
• D. Incomplete dominance

Answer 1

Answer: (C)

A single gene controlling various phenotypes is called pleiotropy. Phenylketonuria is a genetic disorder in which a base substitution occurs in chromosome $12$ is affected. But it affects multiple systems such as brain development, decreased pigmentation and eczema. This is an example of pleiotropy.
If a single phenotype is controlled by several genes, then that type of inheritance is called polygenic inheritance. For example - the color of the skin is controlled by several genes.
When the dominant allele fails to completely dominate the recessive allele, the phenomenon is called incomplete dominance. Example: Pink flower color in snapdragon.
The phenomenon in which a gene which has more than two types of alleles is called multiple allelism. For example: The blood group has three different alleles $(A^A,I^B$ and $i$ ).