Quantitative Inheritance - Polygenic Inheritance.pptx
- 1. Polygenic Inheritance or Quantitative Inheritance Dr. Rashmi Nagesh
- 2. Definition • Polygenic inheritance is defined as some phenotypic character determined by more than one gene. • Polygenic inheritance is commonly known as quantitative inheritance and multiple gene inheritance. • Height, skin pigmentation, eye color, hair color, and milk and egg production are phenotypic characteristics present in plants and animals. • Many traits and phenotypic characters are inherited by many alleles present in different loci, known as polygenic inheritance.
- 3. • It is the type of inheritance controlled by more than one gene where the dominant alleles have a commutative effect, with each dominant allele expressing a part or unit of the trait. • The combined effect of many genes shows a significant effect, but a single gene has little effect on the phenotype. • The full trait is shown if all dominant alleles are present in it.
- 4. Characteristics of polygenic inheritance • Each gene has a too-small effect, which is why it is difficult to detect, but their combined effect is significant and easy to detect. • Each allele has an additive or cumulative effect. • The equal effect is produced by multiple genes. • One phenotypic character or particular trait is controlled by more than one gene. All such genes are non-allelic. • It is difficult to predict phenotype due to the complex pattern of polygenic inheritance. • Polygenic inheritance is occurred by the continuous variation of the phenotype of a trait.
- 5. • Environmental factors and the combined effect of many genes produced continuous variation. • Each gene has a certain amount of effect, and the more the number of dominant genes, more the pronounced its characteristics. The trait becomes much more pronounced due to the addition of several alleles. • Polygenic inheritance is also called cumulative inheritance because the phenotype depends upon the number of dominant alleles present.
- 6. Polygenic Inheritance in human The skin color of human • It is controlled by around 60 loci. • Human skin color is regulated by three pairs of genes. • When a negro black (AA BB CC) phenotype is crossed with pure white (aa bb cc) phenotype, an intermediate phenotype (Aa Bb Cc) is produced.
- 7. • In the F2 generation, (Aa Bb Cc× Aa Bb Cc) will produce different skin colors (i.e., very dark to light). Skin color depends upon melanin pigment. A negro black (with all dominant alleles (AA BB CC) would have the highest amount of melanin, and pure white color (aa bb cc) has a negligible amount of melanin. • The ratio of skin color is following: 1:6:15:20:15:6:1. • The skin color ranges from negro black (AABBCC) in 1/64 individuals very dark brown in 6/64 individuals, dark brown in 15/64 individuals, intermediate brown (AaBbCc) in 20/64 individuals, light brown in 15/64 individuals, very light brown in 6/64 individuals and pure white (aabbcc) in 1/64 individuals.
- 9. Polygenic Inheritance in plants Kernel color of the wheat • Nilsson-Ehle (1908) gave the first experimental evidence of the kernel color of wheat. • kernel color of wheat is determined by 3 independently assorted pairs of alleles. • The dark red wheat kernel has 3 dominant alleles AA BB CC and the white kernel have recessive alleles i.e. aa bb cc. These alleles crossed in the F1 generation produce intermediated red color have (Aa Bb Cc). • In the F2 generation, 1 white and 63 red with varying shades are produced.