Understanding Heterosis and Crossbreeding in Animal Breeding, Study notes of Animal Biology

Download Understanding Heterosis and Crossbreeding in Animal Breeding and more Study notes Animal Biology in PDF only on Docsity! 1 Crossbreeding Plans ANSC327 Spring 2009 Fifth Lecture (Siewerdt) Definitions • Hybridization: mating between animals of different species; the progeny usually infertile (why?) Mating a male ass (jack) with a female horse– (mare) produces a mule – Mating of a male horse (stallion) with a female ass (jenny) produces a hinny • Crossbreeding: mating between animals of different breeds (lines, varieties, strains) Definitions • Heterosis: observed increase in production of crossbred animals compared to the parental breeds )(1 yyyH + • Heterozygosity: proportion of loci in which an organism is a heterozygote )( 100% 212 1 212 BreedBreed BreedBreedCROSSBRED yy HH + × = −= Heterosis: Example • Trait: litter size in pigs • Landrace gilts: average of 8.6 piglets • Large White gilts: average of 10 piglets • Crossbred gilts: average of 11 piglets %3.18 )106.8( 7.1100% 7.13.911)106.8(11 2 1 2 1 = + × = =−=+−= H pigletsH 2 Heterosis: Basis and Types • Genetic basis for heterosis – (Think gene action!) • Individual heterosis: attributed exclusively to the genes that the animal carries • Maternal heterosis: attributed to the genes that the mothers carry that are reflected in the progeny • Paternal heterosis: attributed to the genes of the father, reflected in the progeny Maternal Effect • Effect of the mother’s genotype on the progeny’s phenotype • Symbol: mX (“X” is the breed) – Effect is not observed on the mother’s own phenotype! – Genes are transmitted to progeny through nuclear and cytoplasmic inheritance Working Example, Slide 1 • Male: Merino (M) • Female: Suffolk (S) • Progeny: 50% M, 50% S – Progeny expresses 100% individual heterosis – No maternal heterosis – No paternal heterosis – Maternal effects from the Suffolk breed Working Example, Slide 2 • Male: Merino (M) • Female: Merino x Suffolk cross • Progeny: 75% M, 25% S – Progeny expresses 50% individual heterosis – Progeny expresses 100% maternal heterosis – No paternal heterosis – 50% of maternal effects from the Suffolk breed; other 50% from Merino