What Is the Inbreeding Coefficient?

The inbreeding coefficient quantifies the likelihood that an individual has inherited two copies of the same ancestral allele due to shared ancestry between the parents. This is crucial for understanding the increased risk of recessive genetic disorders in offspring of related individuals.

Calculating the Inbreeding Coefficient for Sibling Marriages

For a marriage between brother and sister (full siblings), the calculation is straightforward:

• Both siblings share the same two parents, so the probability that an allele from the father and an allele from the mother are identical by descent is high.

• The formula for the inbreeding coefficient (F) in this case is:

  F=14=0.25F=41=0.25

• This means there is a 25% chance that any given locus in the child will be homozygous due to inheritance from a common ancestor (the shared parents).

Why Is the Value 0.25?

• Each parent passes one allele to the child, and since the parents are siblings, there is a significant chance that the same allele is passed down both sides of the pedigree.

• For full siblings, the coefficient of relationship is 0.5, and the inbreeding coefficient for their offspring is half of that, i.e., 0.25.

Implications of High Inbreeding Coefficient

• Increased risk of genetic disorders: The higher the inbreeding coefficient, the greater the risk that harmful recessive alleles will pair up, leading to genetic diseases.

• Reduced genetic diversity: High inbreeding can decrease the overall fitness and adaptability of a population.

Correct Answer

The inbreeding coefficient of offspring from a brother-sister marriage is:

(3) 0.25

This value reflects the significant genetic risks associated with close consanguineous unions and underscores the importance of genetic diversity in healthy populations.