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Ranking the animals

36 important questions on Ranking the animals

Why does breeding still remains 'gambling' for an individual animal?

- The breeding value is estimated and therefore not 100% accurate
- Even in you know the breeding value of an animal with 100% accuracy, so you know its the true breeding value, you cannot predict which half of the genetic potential is passed onto each of the progeny due to mendelian sampling

What provides the estimated breeding value on performance?

It is twice the expected performance of offspring compared to the population mean

What is mass selection?

Is based on ranking the animals on their own performance. The success of mass selection is dependent on the heritibility of the trait under selection

When is genomic selection very useful?

- In the case of phenotypes that are very difficult or expensive to measure
- If you want to estimate breeding values for very young animals, before the phenotype can be measured
- Sex-limited traits

What is a disadvantage of genomic selection?

- The reference population needs to be of sufficient size to be able to estimate accurate assocations between genotype and phenotype
- It needs to be updated on a regular bases

What is the true breeding value?

Represent the genetical potential of a animal; what is the real value of the animal for breeding. The perfect EBV would be equal to the TBV

What is the formula for the TBV?

TBV= b * phenotypic deviation + error

How do you calcualte the phenotypic calculation?

= the phenotypic information of the animal - the population average

How is the EBV expressed?

As deviations to the population average

What do you need for the EBV to become as close as the TBV as possible?

Try to find the best regression coefficient and the most informative phenotypic information

What happens when the regression coefficient increases?

The phenotypic information has become a better predictor of the TBV

How can the phenotypic deviation be improved?

By cleaning the data from systematic environmental effects

What does the accuracy of the breeding value estimation represent?

The correlation between the EBV and the true genetic deviation, and has a value between 0 and 1 (100%)

How do you estimate the breeding value for mass selection?

EBVmasselection = h2 * (P-P_)

Where does repeated observations of own performance add to?

The estimation of the regression coefficient. The lower the repeatibillity is, the higher the benefit of repeated observation

How is the EBV of offspring calculated?

EBVoffspring=bsingleparent-offspring*(Psingleparent-P_) = 1/2 h2 * (Psingleparent-P_)

What is the expected performance of an animal?

The population average in absence of other information

What is the formula for the regression coefficient?

The regression coefficient is equal to the additive genetic relationship times the heritability: b=a*h2

What does the regression coefficient to estimate the breeding value use for other sources than own performance?

Depends on the additive genetic relationship, the heratibility, the number of information sources and the size of the shared common effect

What are the three steps to take to estimate a breeding value?

- Determine the phenotypic deviation of your information source
- Determine the regression coefficient
- Combine the previous to estimate the breeding value

What does the presence of a common environmental effect have?

A reducing effect on the estimated breeding value

What is the EBV with phenotypic information of multiple relatives?

The EBV is the sum of phenotypic deviations times multiple regresion coefficients

What is the animal model?

The animal model represents a method that makes use of phenotypic information of relatives to estimate the breeding value of an animal

What is the accuracy of an EBV?

gives an indocation of how likely it is that the EBV is correctly estimated. t this is an indication of the value of the EBV as selection criterion. The accuracy (rIH) is a correlation, but with values between 0-1

Why is information on offspring more value than that of sibs?

Because the offspring receives half of the genes from the animal. If a sufficient nukber of offspring are available then the mendelian sampling effect can be quantified and the EBV of the animal can be estimated very accurately

What happens when the accuracy of an EBV is low?

The risk of a change in EBV when new information sources become available get larger

How can the accuracy reach 1 for traits with low heritability?

When there is information available from sufficiently large number of offspring

What is the best estimate of the breeding value of an animal?

The EBV. The accuracy indicated the risk f a difference between EBV and TBV, where the TBV may be higher or lower with equal probabillity

Why is the accuracy of the EBV of young offspring not equal to the average of their parents?

Because of the relatively large influence of mendelian sampling

What is genomic selection?

Is based on estimation of associations between a very dense set of genetic markers (SNP) and phenotypes on a select group of animals; the reference population

What is the result of genomic selection?

the resulting prediciton equations are then applied to SNP genotypies in the target population to estimate their genomic breeding value (gEBV), without the need of additional phenotypes

Why do reference populations need to be updated regularly?

To maintain associations between SNP and phenotypes

Where is the genetic relationship between reference population and target population influence to?

On the accuracy of genomic selection

Where do the accuracy of genomic selection depend on?

- Heritability
- The number of animals in the reference population
- Population parameter q that reflects the relation between the size of the genome and the level of inbreeding

What can be a limiting factor for the gEBV?

The size of the reference population especially not for traits with a low heritabillity.

What can be a solution for the limiting factor of the gEBV?

To combine forces across breeding associations

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