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

INBREEDING

Inbreeding means the mating together of individuals that are related to each other by ancestry

• Pairs mating at random are more closely related to each other in a small population than in a large one.
• Hence, the properties of small population can be treated as the consequence of inbreeding.
• So the degree of relationship between the individuals in a population depends on the size of the population.
• Genes may be similar or identical due to two different reasons
• Homozygotes – Identical by descent
  • Two genes are identical by descent (autozygous) if they are biochemical replicates produced without mutation from a common ancestral gene.
• Homozygotes - Alike in state (independent/ allozygous)
  • Two genes are regarded as alike because of their nucleotide sequence and similar function.

Inbreeding coefficient

• Inbreeding coefficient is probability that the two genes at any locus in an individual are identical by descent.
• The symbol for coefficient inbreeding is F.

Panmictic index is the probability that genes at any single locus are independent by descent P = (1 – F)

• The inbreeding coefficient of subsequent generations expresses the amount of dispersive process that has taken place since the formation of the base population.
• The amount of dispersive process expressed in terms of increment of inbreeding or rate of inbreeding is ΔF = 1/2N
  • Where ΔF is the increment in inbreeding in each generation and N is the number of breeding individuals in the population.
• Therefore, the increment of inbreeding can be used instead of the population size to estimate the variance of change of gene frequency