23: Genetic Change and Genetic Prediction Flashcards
Genetic Prediction is the area of animal breeding concerned with what?
Measurement of data, statistical procedures, and computational techniques for predicting breeding values and related values
Four methods for genetic prediction
- mass selection
- selection index
- best linear unbiased prediction (BLUP)
- genomic selection
What is mass selection
Selection based solely on an individual’s own phenotype
Animals ranked based on their performance (no pedigree info, performance data of sibs, parents, progeny)
Mass selection selects members of breeding stock exhibiting…
desirable qualities, or eliminates those showing undesirable ones
Mass selection increases the occurrence of…
desirable genes in a population
How does mating work in mass selection
Animals with superior characteristics are selected and allowed to mate at random
When will results from mass selection be the best?
With high heritability of the trait (phenotype is a good indicator of genotype)
Why is mass selection usually not the choice?
We have other sources of information, such as performance of relatives (dam, sire, siblings, progeny)
More info = more accurate EBV
What is selection index
Linear combination of various kinds of phenotypic information and appropriate weighting factors
What sources of information are used for selection index
Individual’s own performance record, pedigree data, progeny data
Selection indexes should only be used for…
genetic prediction when performance data comes from contemporary groups thought to be genetically similar
What is a contemporary group
A group of animals that have experienced a similar environment with respect to the expression of a trait
Factors affecting the accuracy of selection index
Number of records, heritability of the trait, pedigree relationship
What is the Best Linear Unbiased Prediction (BLUP)
Extension of selection index methodology that requires intensive computation
Allows the use of phenotypic info of genetically different contemporary groups (diff farms and herds)
BLUP is the preferred method for…
large-scale genetic evaluation/prediction using performance records collected from the field
The BLUP model accounts for…
differences in the mean BVs of contemporary groups
BLUP accounts for…
selection over time and accepts non-random mating of sires and dams
BLUP can be thought of as a …
family of statistical models, including various genetic and environmental effects
What is Animal Model
genetic statistical model that combines phenotypic information of related animals to achieve a better estimate of the breeding value for the animal
Important advantages of the Animal Model
- Dont necessarily need a record from each and every animal to be able to estimate its BV
- Even if we have a phenotype, the extra info on related animals increases the accuracy of EBV
What is genomic selection
Based on estimation of detailed associations between a very dense set of genetic markers (SNPs) and phenotypes on a select group of animals (reference population)
Factors affecting accuracy of genomic selection
- trait heritability
- number of SNPs (higher better)
- population size (large better)
- genetic relationship between populations (closer relationship = better estimate of SNP effects)
Benefits of genomic selection
- Decrease generation interval due to estimation of BVs for young animals before they have their own performance
- Reduce need for phenotyping for hard/expensive to measure phenotypes
Genomic selection useful for selection of traits that are…
- very difficult or expensive to measure
- expressed later in life
- lowly heritable
- measured in only one sex
Why do reference populations for genomic selection need to be updated on a regular basis
Associations between SNP and phenotype may be lost across generations
Genomic estimated breeding value (GEBV) estimates…
the effect of each SNP marker and its association with the phenotypes economically important traits
