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Heterosis Genotype x Environment Interaction

Heterosis Genotype x Environment Interaction. Two General Methods of Assortative Matings / Breeding. 1. Close breeding, Inbreeding mating of two related individuals 2. Outbreeding * mating of unrelated individuals . * Today’s topic. Outbreeding Three categories:

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Heterosis Genotype x Environment Interaction

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  1. Heterosis • Genotype x Environment Interaction

  2. Two General Methods of Assortative Matings / Breeding 1. Close breeding, Inbreeding mating of two related individuals 2. Outbreeding * mating of unrelated individuals *Today’s topic

  3. Outbreeding Three categories: LineCrossing - mating of unrelated animals within the same breed or 2 lines within the same breed. aka . Outcrossing BreedCrossing - Mating of animals from different breeds aka . Crossbreeding SpeciesCrossing - Breeding of different animal species e.g. dog and wolf

  4. Genetic Effect of Outbreeding • number of gene loci that are heterozygous • degree of heterozygosity • Species Crossing > Breed Crossing > Line Crossing

  5. Phenotypic Effect of Outbreeding progeny* usually but not always perform > than the parents. Performance = hybrid vigor ; measurement = heterosis. * Progeny could perform worse than the parents

  6. Example Calculation of Heterosis Lamb weaning weight Purebred Hampshire mean = 58.3 lb Suffolk = 73.3 lb Mean of the 2 purebreds = 65.8 lb Hampshire - Suffolk hybrid mean = 72.5 lb heterosis = (mean of hybrids - mean of parents) x 100 mean of parents = 72.5-65.8 x 100 = 10.2 % 65.8

  7. Heterosis and Factors That Influence It • Genetic diversity of the parents • - The more dissimilar the parents > heterozygosity in the outbred individuals.

  8. Heterosis and Factors That Influence It...... • Non additive gene actions contribute • - Dominance, recessiveness, overdominance, epistasis in contrast to additive genes • - Heritability inversely associated with heterosis low h2, higher heterosis, etc.

  9. Heterosis and Factors That Influence It....... • Compounding the heterotic effects • - Heterosis is enhanced in multi-way crosses

  10. Individual + Maternal ((AxB) x C) Individual AxB

  11. Genotype-Environment (GxE) Interaction

  12. GxE = a situation where the same genotype responds differently in dissimilar environments -different phenotypic responses

  13. Environment: -nutrition (diets); - animal’s management protocol; - endemic pathogens (bacteria, viruses, mycoplasmas); - climate (temp., humidity, day- length; dist. to the ocean, etc.); - altitude, geography, etc.

  14. Relative Phenotypic Ranking Types of GxE Interaction None

  15. Example, Genotype x Environment, location

  16. Genotype x Environment, Vitamin (biotin)

  17. Example of GxE, Performance of Cattle in a Hot Environment 120 100 Holstein 80 Cross Bred Respirations 60 Zebu per min 40 20 0 11 19 23 29 36 Temperature, C

  18. Three Features of the GxE: • Difficult to predict in advance if the GxE will be important.

  19. Features of the GxE...... • Breeder must be aware of the animal’s response in different environments.

  20. Features of the GxE...... • Conduct comparisons in all relevant environments.

  21. Breeder’s Dilemma/Predicament: In which environment do youconduct genetic selection to improve the desired phenotypic trait? (Examples - environment for disease resist., contaminated vs aseptic environment - breed in Corvallis for an animal destined for E. OR)

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