Polygenic Inheritance in Biology

Polygenic Inheritance

Polygenic inheritance is a type of inheritance where multiple genes contribute to a single trait or phenotype. Unlike monogenic inheritance, where a single gene controls the expression of a trait, polygenic inheritance involves the interaction of multiple genes. In this type of inheritance, alleles do not display dominance over others, instead, each contributing allele gives an additive effect.

For example, in the case of height, multiple genes control the expression of this trait. Some genes may contribute to increased height, while others may contribute to decreased height. The combination of these genes determines the overall height of an individual.

In polygenic inheritance, the expression of a trait is often influenced by environmental factors, making it difficult to predict the exact outcome. This is because the interaction between genes and environment is complex, and small changes in either can result in significant differences in the expression of the trait.

The study of polygenic inheritance is important in understanding the genetic basis of complex traits and diseases. It has applications in fields such as agriculture, where scientists can breed crops with desirable traits, and in medicine, where it can help identify individuals at risk of certain diseases.

Inheritance

• In polygenic inheritance, alleles do not display dominance over others, instead, each contributing allele gives an additive effect.

Skin Tone Example

• A simplified example of polygenic inheritance uses two parents, heterozygous for each of the melanin-producing genes (AaBbCc x AaBbCc).
• There are 64 possible allele combinations, resulting in 7 different colored skin tones.
• The skin tones that are least likely to occur are those resulting from entirely homozygous genotypes.
• The lightest skin tone (aabbcc) lacks any alleles contributing melanin pigment, and the darkest skin tone (AABBCC) contains all possible contributing alleles.
• Each of these phenotypes occurs at a probability of 1/64.

Kernel Color in Wheat

• Nilson-Ehle (1909) demonstrated the segregation and assortment of genes with quantitative effect in wheat.
• He crossed red-kernelled wheat with a white kernelled strain, resulting in five phenotypes in the F2 generation.
• It was theorized that two pairs of genes control the production of red pigment in wheat.
• The cross follows: AABB X aabb, resulting in 16 possible genotypes and phenotypes.

Genotype-Phenotype Relationships

• The genotype and phenotype relationships are as follows:
  • AABB: dark red
  • AABb: medium red
  • AaBB: medium red
  • AaBb: intermediate red
  • Ab: medium red
  • AAbb: intermediate red
  • AaBb: intermediate red
  • Aabb: light red
  • aB: medium red
  • AaBB: medium red
  • AaBb: intermediate red
  • aaBB: intermediate red
  • aaBb: light red
  • aabb: white