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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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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


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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


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  • Genetic Effect of Outbreeding

    • number of gene loci that are heterozygous

    • degree of heterozygosity

  • Species Crossing > Breed Crossing > Line Crossing


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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


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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


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  • 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.


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Individual + Maternal

((AxB) x C)

Individual AxB



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GxE = a situation where the same genotype responds differently in dissimilar environments

-different phenotypic responses


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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.


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Relative

Phenotypic

Ranking

Types of GxE Interaction

None


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Example, Genotype x Environment, location



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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


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  • Features of the GxE......

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


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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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