Inbreeding depression

• Inbreeding or consanguineous mating is mating between individuals related by descent or ancestry.
• The degree of inbreeding of an individual is expressed as inbreeding coefficient (F).
• When the individuals are closely related, e.g., in brother-sister mating or sib mating, the degree of inbreeding is high.
• Inbreeding depression may be defined as the reduction or loss in vigour and fertility as a result of inbreeding.
• Inbreeding depression = F1-F2 / F1 x 100

 

Effects of inbreeding

1. Appearance of Lethal and Sublethal Alleles :

• IB results in appearance of lethal; sublethal and sub vital characters.
• Eg : Chlorophyll deficiencies, rootless seedlings, flower deformities – They do not survive, they lost in population.

2. Reduction in vigor :

• General reduction in vigor size of various plant parts.

3. Reduction in Reproductive ability :

• Reproductive ability of population decreases rapidly.
• Many lines reproduce purely that they cannot be maintained.

4. Separation of the population into distinct lines :

• Population rapidly separates into distinct lines i.e. due to increase in homozygosity.
• This leads to random fixation of alleles in different lines.
• Therefore, lines differ in genotype and phenotype. It leads to increase in the variance of the population.

5. Increase in homozygosity :

• Each lines becomes homozygous.
• Therefore, variation within a line decreases rapidly. After 7-8 generations of selfing the line becomes more than 99% homozygous. These are the inbreds. These have to be maintained by selfing.

6. Reduction in yield :

• IB leads to loss in yield.
• The inbreds that survive and maintained have much less yield than the open pollinated variety from which they have been developed.