Exam 4 Flashcards
Heritability can be estimated by the ___, ___ between genetics values and phenotypes
squared correlation, regression
Repeatability can be estimated by the ___, ___ between genetics values and phenotypes
Squared correlation, regression
Two variables involved in calculating heritability
Breeding values (genetic values) & Phenotypes
Two variables involved in calculating repeatability
PA & Phenotypes
Define heritability
Percent trait variation that can be explained by genetic differences among animals
Important use for heritability
Use heritability to predict BV
What is the essential principle involved in the several approaches to increasing heritability and repeatability
Decrease environmental variation
Ways to increase heritability and repeatability
- treating animal groups more similar
- Increase # of records on animal
- Make more accurate measurements
- Use contemporary grouping
How does increasing heritability and repeatability benefit produces
It increases the accuracy of selection
Why do quantitative animal breeders manipulate animal performance data by applying adjustments for factors such as age, sex, contemporary group effect, type of birth (single, twin, etc.) etc. etc.
To eliminate environmental effects which increases the accuracy of selection
What is adjustment for contemporary group average and age of dam important in calculating breeding values for birth weight
- Increase accuracy of selection
- Removing environment effects
Why do actual breeding values not line up exactly on the regression line
Because phenotype does not equal BV, because of E and GCV
What size contemporary groups provide the best estimate of group average
Large groups
What is the range of possible values for heritability
0-1
Why is heritability for a trait not constant among different groups of animals
Because the herds may be managed differently & one herd may use contemporary grouping
Define contemporary group
A group of animals that have been managed similarily
Why should producers use contemporary grouping
increase the accuracy of selection
Why would livestock producers calculate ratios of trait values
Because it is easier for producers to see which animals are above or below the mean
Why should data on all of producers’ animals be reported to breed associations
Because the average animals in the herd will look bad if the poor animals are not reported
4 factors that affect rates of genetic gain in a herd or breed
- Selection accuracy
- Selection intensity
- Genetic variation
- Generation interval
What piece of info is needed to find appropriate selection intensity value on the truncation table
The proportion of the population that is saved
What does it mean when we say that EBV is an “unbiased” estimate of true breeding value
As we add more info for calculating that EBV, it is equally likely to increase as it is to decrease
Which selection method is used by breed associations
BLUP (Best Linear Unbiased Prediction)
Why is BLUP used instead of selection index
- Accounts for genetic trends
- Accounts for non-random mating
- Accounts for contemporary grouping
- Uses all available info on an animal
- Accounts for culling for poor performance
- Estimates maternal and paternal genetic trends
Why are large scale genetic evaluations more often used on sire summaries than on dam summaries
Because 1 sire will have more effect on the herd than will 1 dam
