Inbreeding is a phenomenon in which related individuals with similar genotypes preferentially mate with each other. The extreme form is self-fertilization.
- Inbreeding occurs in nonrandom mating.
- it will not change the overall gene frequency
- it will lead to an excess of the homozygous genotype
- offering selection increased opportunity to act on rare recessives
- F is the inbreeding coefficient that measures the probability of two alleles of a gene in a diploid zygote are identically descended from the single ancestral allele.
- Alleles segregate by Mendles law and their probability will be 1/2
- so in F1 generation alleles have 1/2 chance that offspring receive the same ancestral allele
- And when 2 F1 mates the chances in the next generation to get an identical allele is 1/8.
Interpretation of the equations :
- identical means homozygosity i.e AA and aa.
- the inbred proportion is given as PF= AA and qF=aa genotypes
- The outbred population (1-F)that is the remaining population is given according to hardy Weinberg equilibrium p2=AA 2pq=Aa and q2 = aa
- pqf is the factor causes increase in the frequency of homozygotes and causes a decline equally in heterozygotes types
- when inbreeding is absent F=o and equations proceeds to hardy Weinberg equation
- when inbreeding is complete F=1 , 2pq-2pqF=0 and the remaining genotypes are pAA and qaa
Inbreeding depression
some degree of inbreeding can occur in outbreeding populations.
when rare deleterious recessive homozygous genotypes appear due to excessive inbreeding the phenomena occur called inbreeding depression
deleterious recessive appears with increased homozygous frequencies. if a recessive aa with diseased genotype occurs with frequency q2 in a random outbred population its frequency will increase by pqf
the ratio of inbred to outbred will be given as
Example of inbreeding depression: in various outbred pops such as the corn inbreeding depression can reduce Height yield .Inbreeding depression is not universal phenomena in all species certainly that are self fertilized and delete most of deleterious recessives. But in cross fertilization inbreeding depression leads even to extinction.