Question

What do you mean by polygenic inheritance? Describe with suitable example.

Hint:

Polygenic traits are influenced by multiple genes, each contributing a small amount to the overall phenotype, resulting in continuous variation.

Answer 1

Polygenic Inheritance:
Polygenic inheritance refers to the type of inheritance in which a characteristic is determined by the combined effects of two or more genes, and these genes are often located at different loci on different chromosomes. Unlike Mendelian inheritance, where a single gene controls a trait with distinct dominant and recessive alleles, polygenic traits exhibit a continuous range of phenotypes. These traits are often quantitative and show a gradual change, rather than the discrete classes seen in Mendel's experiments. In polygenic inheritance, each gene contributes a small, additive effect to the overall phenotype. As a result, the phenotype does not follow the simple dominant/recessive pattern, and the expression of the trait can vary along a spectrum. This continuous variation leads to a wide range of phenotypic expressions, such as height, skin color, and weight. ### Characteristics of Polygenic Traits: 1. **Multiple Genes Involved:** More than one gene controls the trait. 2. **Continuous Variation:** The trait shows a range of phenotypes, rather than discrete categories. 3. **Additive Effect:** Each gene contributes additively to the overall phenotype, so the more dominant alleles present, the more pronounced the trait. ### Example of Polygenic Inheritance: Human Skin Color: Human skin color is a classic example of polygenic inheritance. It is controlled by the interaction of several genes, each contributing to the overall pigmentation of the skin. The primary genes involved are located on different chromosomes, and each gene has multiple alleles that contribute to skin pigmentation. - Individuals with darker skin have more of the dominant alleles for pigmentation, leading to higher amounts of melanin. - Individuals with lighter skin have a greater number of recessive alleles for pigmentation, resulting in less melanin production. The combination of alleles from each gene creates a continuous spectrum of skin tones, from very light to very dark. ### Other Examples of Polygenic Inheritance: - **Human Height:** Height is determined by the interaction of multiple genes. While each gene has a small effect on an individual's height, the overall combination of alleles determines whether a person is short, average, or tall. - **Intelligence:** Like height and skin color, intelligence is influenced by multiple genes, although environmental factors also play a significant role. ### Mendel's Model vs. Polygenic Inheritance: Unlike Mendel's experiments, where traits were controlled by single genes with clear dominant and recessive alleles, polygenic inheritance involves multiple genes that interact to produce a range of phenotypes. Therefore, polygenic inheritance patterns do not follow the simple Mendelian ratios of 3:1 or 1:2:1 but rather produce bell-shaped curves when the phenotypic distribution is plotted.