Lec 19

• Genotype x Environment Interaction (GEI)


  P = G + E + G x E<|>If G and E act independently then no GEI<|>GEI is a situation where different genotypes (breeds, strains, lines) respond differently in different environments<|>Different response includes changes in mean performance and variability in performance of different genotypes
• Commercial poultry breeders often compare performance between purebred lines and their crossbred progenies which are distributed to commercial farms
• Environments

  • Breeder farm
  • Commercial farms
• Genotypes


  • Purebred lines
  • Crossbred progenies
• Genotype differences


  Increase with increasing divergence between environments
• 1. Way Analysis of Variance for GEI

  1. Mean Squares

  2. Total

  3. Genotypes (G)

  4. Environments (E)

  5. G x E (Error)
• Genotype x Environment Interaction


  Different from correlation between genotypes and environments, r
• Examples of GEI

  • Better environments are provided to better genotypes
  • High producing cows receive more feed
• Rank correlation


  Compute Spearman (rank) correlation of genotype evaluation in different environments<|>If rank correlation is 1.0, genotypes rank same in different environments
• GEI classification according to Haldane (1946)


  • Ranking the same, bigger difference
  • Ranking the same, smaller difference
  • Significant GEI, reranking
  • Significant GEI, reranking & scaling effect
• Falconer (1952) on GEI


  A trait assessed in 2 different environments considered as 2 distinct traits but treated as correlated traits<|>Use genetic correlation between Trait 1 in Environment A and Trait 2 in Environment B to check for GEI
• Genetic correlation r_G


  If r_G < 1 it means there is some re-ranking (or rescaling) of genotypes<|>Example: Sire x Region, if r_G is much smaller than 1.0 there should be a different sire listing for different regions
• 2 possible effects when GEI is present

  • Scaling effect - Ranking of sires the same in the 2 environments, but the sire differences may be smaller/bigger in 1 environment than the other environment
  • Re-ranking of genotypes - Genotypes perform differently in different environments and requires a different list of genotype ranking in the other environment
• Example of GEI with scaling effect

  • Charolais crossbred cattle had better ADG than KK cattle on both native and improved pastures, but the magnitude of differences in performance between the 2 breeds was smaller on native pasture compared to improved pasture
• Genotype x Environment Interaction is commonly used in plant breeding, where many crops have different varieties meant for planting in different parts of the country
• Predictable (fixed) environments


  • Feeding level or type
  • Disease or parasitic load
  • Climate differences
  • Maternal environment in breed of dam
• Ideally, the goal is to select breeds or individuals for performance in the target environment
• Unpredictable (random) environments


  • Year - season - herd
• Multi-locational trials are commonly done in crop varietal assessment to evaluate breed suitability across a range of environments
• Interactions with region

  • Breed x region interaction
  • Sire x region interaction
• Interactions with sire

  • Sire x region
  • Sire x herd
  • Sire x breed of dam
• If sire x region interaction, evaluate sires unique for each region
• If sire x breed of dam interaction, use some specific sires depending on breed of dam
• Study to identify best system for dairy cattle (Kearney et al, 2004)

  1. Testing different genotypes (sires) in 2 environments/management systems (Grazing & Confinement)

  2. Questions:

  3. Is there G x E Interaction - Sire x Management System?

  4. Is there a scaling effect - Is ranking of sires the same in the 2 environments?

  5. Results:

  6. Some GEI as indicated by genetic correlation between traits in 2 environments (r_G < than 1)

  7. Re-ranking of sires
• Examples of GEI studies

  • Milk yield of strains of Holstein cows in Mexico & USA (Significant GEI)
  • Milk yield of strains of Holstein cows in Canada & New Zealand (Significant GEI)
  • Milk, fat & protein yield of high merit imported animals and medium genetic merit animals for 3 intensive grazing systems (Non-significant GEI)
  • Milk yield of heifers of imported vs NZ origin on pasture (Non-significant GEI, but foreign more weight loss)
• Commercial poultry breeders have improved control over genotypes and environments, allowing them to reduce GEI variance
• Commercial poultry breeders develop strains matching specific environmental conditions, such as strains for hot environments and strains for cooler climates, as well as strains for specific nutrient levels
• Commercial poultry breeders have developed strains specific to nutritional environments, such as strains for maize and soybean based diets which are used worldwide, and strains for intensive rearing in enclosed houses
• Examples of specific poultry strains

  • Rhode Island Red
  • White Leghorn
• Poultry industry questions on GEI

  • Will GEI increase with worldwide distribution of poultry strains?
  • Should selection lines be bred in optimal or stress environments?
  • Should the breeding goal be general or specialized adaptability?
  • Should selection be under uniform & optimal conditions, less than optimum, or specific strains for unique adaptation to specific environments?
• Selection objectives for most poultry markets

  • Rapid growth
  • Good conformation and feed efficiency
  • Low variability in body weight
  • High yield of saleable meat, especially prime cuts - breast meat
• Developing livestock strains for a tropical hot humid environment requires considering environmental characteristics like high temperature, high humidity, and prevalent disease organisms
• Reducing adverse GEI can be done by using crossbreds in different environments due to greater tolerance and resistance to environmental stress
• Taking advantage of beneficial GEI can be done by using purebred lines