Understanding Heterosis and Crossbreeding in Animal Breeding: A Case Study of Pigs - Prof., Study notes of Animal Biology

Download Understanding Heterosis and Crossbreeding in Animal Breeding: A Case Study of Pigs - Prof. and more Study notes Animal Biology in PDF only on Docsity! 1 Unit 6: Crossbreeding Lecture: “Heterosis” ANSC450 Spring 2009 Day 33 (April 17) 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 + × = −= 2 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 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