Gene Interaction - An Overview MCQ - Practice Questions with Answers

• Gene interaction can be classified as:
  • Allelic or Non-epistatic gene interaction: When two different genes contribute their individual effect to their respective phenotypes and do not interfere with the expression of other such genes. This type of interaction gives the classical ratio of 9:3:3:1.
  • Non-allelic or Epistatic gene interaction: In this type of gene interaction, genes located on the same or different chromosomes interact with each other to produce a phenotype. This type of interaction results in deviation from the classical Mendelian ratio of 9:3:3:1
• Gene interaction can be defined as a phenomenon of two or more genes affecting the expression of each other in various ways in the development of a single character of an organism.
• The following types of gene interactions will be studied:
  • Dominant epistasis (12:3:1)
  • Supplementary gene interaction or recessive epistasis (9:3:4)
  • Complementary factor (9:7)

Polymorphic gene or polymeric gene interaction (9:6:1)

• Inhibitory gene action (13:3)
• Duplicate gene action (15:1)
• Note:
  • Epistatic Gene: When a gene suppresses or masks the expression of another gene, it is said to be an epistatic gene.
  • Hypostatic Gene: The gene which is suppressed by the epistatic gene is called the hypostatic gene.

• In this type of gene interaction, two non-allelic genes controlling a character produce identical phenotype when they are alone, but when both the genes are present together their phenotypes effect is enhanced due to cumulative effect. 
• In barley, two genes A and B affect the length of awns.
• Gene A or B alone gives rise to awns of medium length (the effect of A is same as B); but when both present, long awn is produced; absence of both results aweless.