Interaction of genes: Epistasis, Codominance and incomplete dominance
Download as PPTX, PDF1 like1,374 views
The document discusses gene interactions, specifically epistasis, codominance, and incomplete dominance. It defines epistasis as the suppression of gene expression by a non-allelic gene and details types of epistatic interactions, including recessive and dominant epistasis, along with examples involving coat color in mice and dogs. Additionally, it explains codominance and incomplete dominance with examples from human blood groups and snapdragons.
Interaction of genes: Epistasis, Codominance and incomplete dominance
- 1. Interaction of genes Epistasis, Codominance and Incomplete dominance By, Dr. Manoj K. Bangadkar
- 2. • Phenotypic expression of a gene may be altered by the influence of other gene • The modification of the normal phenotype of certain genes is known as gene interaction. • Gene interaction is of two types – Intergenic or non allelic gene : Occurs between alleles of different gene to alter normal phenotype – Ex. Complementary gene, Supplementary gene, Polygenes, Epistasis, Pleotropy and Lethal genes – Intragenic or allelic gene : Occurs between alleles of same gene to alter normal phenotype – Ex. Incomplete dominance, Codominance and Multiple alleles Gene Interaction
- 3. Epistasis • Phenomenon of masking or supressing the expression of geneby another non allelic gene • The gene which supressed by the presence of non allelic gene is termed as hypostatic gene • The term epistssis is coined by Bateson in 1909 • Various types of epistatic gene interaction are – Recessive epistasis – Dominant epistasis
- 4. Recessive Epistasis (Supplementary genes) • Form of gene interaction, in which homozygosity for a recessive allele at one locus can mask the phenotypic expression of a second gene • It has the characteristic 9:3:4 ratio of phenotype • Example: Coat color in Mice – If allele, C = Black coat color c= Albino (Colorless coat) i.e. it has no effect A= Supplementary gene - When black coat mice is crossed with albino mice, the F1 generation is Agouti. It mean here the effect of non allelic gene is changed
- 6. Dominant Epistasis • The dominant allele at one locus mask (supress) the expression of alleles at a second locus • The F2 ratio is generally 12:3:1 • Example: Coat color in Dog – Three types of pigmentation occurs in dog- white, black and brown
- 7. Codominance • Sometimes when neither alle is dominant, both alleles are expressed independently in the heterozygotes • Example- • AB Blood group: In the human AB blood type allele for type A (IA) blood and type B (IB) blood group are codominant so when they come together in an individual they produce blood group AB
- 8. Incomplete dominance • Sometimes two genes of allelomorphic pair do not show dominant recessive relationship, but when present simultaneously (or come together) they show intermediate condition which is called incomplete dominance • Example- Incomplete dominance in snapdragon