Inbreeding - Calculation

Calculation

The inbreeding is computed as a percentage of chances for two alleles to be identical by descent. This percentage is called "inbreeding coefficient". There are several methods to compute this percentage, the two main ways are the path method and the tabular method.

Typical inbreeding coefficient percentages are as follows, assuming no previous inbreeding between any parents:

• Father/daughter, mother/son or brother/sister → 25% (1⁄₄)
• Grandfather/granddaughter or grandmother/grandson → 12.5% (1⁄₈)
• Half-brother/half-sister → 12.5% (1⁄₈)
• Uncle/niece or aunt/nephew → 12.5% (1⁄₈)
• Great-grandfather/great-granddaughter or great-grandmother/great-grandson → 6.25% (1⁄₁₆)
• Half-uncle/niece or half-aunt/nephew → 6.25% (1⁄₁₆)
• First cousins → 6.25% (1⁄₁₆)
• First cousins once removed or half-first cousins → 3.125% (1⁄₃₂)
• Second cousins or first cousins twice removed → 1.5625% (1⁄₆₄)
• Second cousins once removed or half-second cousins → 0.78125% (1⁄₁₂₈)
• Third cousins or second cousins twice removed → 0.390625% (1⁄₂₅₆)
• Third cousins once removed or half-third cousins → 0.1953125% (1⁄₅₁₂)

An inbreeding calculation may be used to determine the general genetic distance among relatives by multiplying by two, because any progeny would have a 1 in 2 risk of actually inheriting the identical alleles from both parents.

For instance, the parent/child or sibling/sibling relationships have 50% identical genetics.