Coancestry and Inbreeding: Consequences and Calculations - Prof. Frank Siewerdt, Study notes of Animal Biology

Download Coancestry and Inbreeding: Consequences and Calculations - Prof. Frank Siewerdt and more Study notes Animal Biology in PDF only on Docsity! 1 Consequences of Selection: Coancestry and Inbreeding ANSC450 Spring 2009 Day 26 (April 1, 2009) Definitions • Coancestry: measures if alleles are identical by descent (ibd) – Always computed for two individuals • Inbreeding: mating between relatives C t d f i di id l f l ti– ompu e or one n v ua or or a popu a on • Relatives are animals that share at least one common ancestor – Half-sibs – First cousins – Father and daughter • Coancestry and inbreeding are related concepts Sample Pedigree • Arrows indicate gene flow • Mendelian inheritance: one-half of the alleles transmitted from parent to progeny A B DC H • Which animals are inbred? • What is the coancestry between D and Y? And between B and D? • Are G and X relatives? • Common assumptions for unknown ancestors and base generation animals FK GE XY 2 The Coefficients • Coancestry coefficient (fXY): probability that a randomly chosen allele from an individual is ibd to a randomly chosen allele from another individual fXY = P(ai ≡ bj) P(ai ≡ bj) = P(a1 ≡ b1) + P(a1 ≡ b2) + P(a2 ≡ b1) + P(a2 ≡ b2) • Clarification – Identity by descent (ibd): copy of same original allele – Identity by state (ibs): same type of allele only The Coefficients (2) • Inbreeding coefficient (FX): probability that an individual is homozygote in a randomly chosen locus due to ibd – Sum over all paths between parents of X – A is the common ancestor – n is the number of individuals in each path, (including the parents) ( ) ( )∑ += AnX FF 121 Bridging the Concepts • FX: inbreeding of X • fCD: coancestry of C and DA FX = fCD • The inbreeding of an individual is equal to the coancestry of its parents YX DC E