AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

Modifications of Mendelian dihybrid ratio

GENE INTERACTION

• The phenomenon of two or more genes governing the development of a single character in such a way that they affect the expressions of each other in various ways is known as Gene Interaction .
• Gene interactions can be classified as,
  1. Allelic gene interaction
  2. Non-allelic gene interaction.

Non-allelic gene interaction

• Expression of character is produced by interaction between two or more genes.
  a) Inter-allelic

i. Without modification of normal F2 ratio.
ii. With modification of normal F2 ratio.
 Such kinds of interactions modify the normal F2 ratio (9:3:3:1). Various types of such interactions are as below.

1. Complementary Gene Interaction
2. Supplementary Gene Interaction
3. Epistasis
4. Duplicate Factor
5. Inhibitory Factor
6. Polymerism or Additive Factor

b) Intra-allelic

i. Lethal  Gene

Allelic gene interaction

• Expression of character is produced by interaction between alleles of a single gene.

1. Complete dominance
2. Incomplete dominance
3. Co-dominance
4. Over Dominance