Heterosis

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• Heterosis
• Genotype x Environment Interaction

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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
Todays topic
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Outbreeding Three categories Line Crossing -
mating of unrelated animals within the same breed
or 2 lines within the same breed. aka .
Outcrossing Breed Crossing - Mating of animals
from different breeds aka . Crossbreeding Specie
s Crossing - 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 gt Breed Crossing gt Line
  Crossing

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Phenotypic Effect of Outbreeding progeny
usually but not always perform gt 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
• Genetic diversity of the parents
• - The more dissimilar the parents gt
  heterozygosity in the outbred individuals.

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

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Individual Maternal ((AxB) x C)
Individual AxB
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Genotype-Environment (GxE) Interaction
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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) - animals
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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Genotype x Environment, Vitamin (biotin)
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(No Transcript)
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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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• Three Features of the GxE
• Difficult to predict in advance if the GxE will
  be important.

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• Features of the GxE......
• Breeder must be aware of the animals response
  in different environments.

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

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Breeders Dilemma/Predicament In which
environment do you conduct 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)