Identity-By-Descent Worksheet

 

Objective:         Calculate IBD for a sib-pair

                        Assess the effects of allele frequency on IBD

 

Consider two siblings homozygous for a ‘1’ allele with frequency p = f(‘1’).  Parental genotypes are missing.

 

 

IBD      Expectation                                          For p = 0.5 and 0.9, calculate

                                    Likelihood                                IBD Distribution                             

                                                                   Probability [P(2), P(1), P(0)]

 

2          ¼ p2                 .0625  _.2025              __.444_           _.277__                       _.666  .527__

 

1          ½ p3                 .0625  _.3645              __.444_           _.499__                      

 

0          ¼ p4                 .0156  _.1640              __.111_           _.152__                      

            SUM                .1406  _.731

 

 

Where do these values come from?