r= coefficient of relationship between two individuals likelihood of sharing by descent a given allele at a given locus expected proportion of all alleles (at all genes)that two individuals share by descent coefficient of relationship, r inbreeding coefficient, F likelihood that an individual is homozygous by descent at a given locus Relationship degree Parent-child 1st 1/2 Siblings 1/2 Aunt/niece 2nd 1/4 First cousins 3rd 1/8r = coefficient of relationship between two individuals = likelihood of sharing by descent a given allele at a given locus = expected proportion of all alleles (at all genes) that two individuals share by descent coefficient of relationship, r ≠ inbreeding coefficient, F (likelihood that an individual is homozygous by descent at a given locus) First cousins Aunt/niece Siblings Parent-child Relationship degree r 1st 1/2 1st 1/2 2nd 1/4 3rd 1/8