Exam 4

Question 1

Heritability can be estimated by the ___, ___ between genetics values and phenotypes

Answer 1

squared correlation, regression

Question 2

Repeatability can be estimated by the ___, ___ between genetics values and phenotypes

Answer 2

Squared correlation, regression

Question 3

Two variables involved in calculating heritability

Answer 3

Breeding values (genetic values) & Phenotypes

Question 4

Two variables involved in calculating repeatability

Answer 4

PA & Phenotypes

Question 5

Define heritability

Answer 5

Percent trait variation that can be explained by genetic differences among animals

Question 6

Important use for heritability

Answer 6

Use heritability to predict BV

Question 7

What is the essential principle involved in the several approaches to increasing heritability and repeatability

Answer 7

Decrease environmental variation

Question 8

Ways to increase heritability and repeatability

Answer 8

• treating animal groups more similar
• Increase # of records on animal
• Make more accurate measurements
• Use contemporary grouping

Question 9

How does increasing heritability and repeatability benefit produces

Answer 9

It increases the accuracy of selection

Question 10

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.

Answer 10

To eliminate environmental effects which increases the accuracy of selection

Question 11

What is adjustment for contemporary group average and age of dam important in calculating breeding values for birth weight

Answer 11

• Increase accuracy of selection

- Removing environment effects

Question 12

Why do actual breeding values not line up exactly on the regression line

Answer 12

Because phenotype does not equal BV, because of E and GCV

Question 13

What size contemporary groups provide the best estimate of group average

Answer 13

Large groups

Question 14

What is the range of possible values for heritability

Answer 14

0-1

Question 15

Why is heritability for a trait not constant among different groups of animals

Answer 15

Because the herds may be managed differently & one herd may use contemporary grouping

Question 16

Define contemporary group

Answer 16

A group of animals that have been managed similarily

Question 17

Why should producers use contemporary grouping

Answer 17

increase the accuracy of selection

Question 18

Why would livestock producers calculate ratios of trait values

Answer 18

Because it is easier for producers to see which animals are above or below the mean

Question 19

Why should data on all of producers’ animals be reported to breed associations

Answer 19

Because the average animals in the herd will look bad if the poor animals are not reported

Question 20

4 factors that affect rates of genetic gain in a herd or breed

Answer 20

• Selection accuracy
• Selection intensity
• Genetic variation
• Generation interval

Question 21

What piece of info is needed to find appropriate selection intensity value on the truncation table

Answer 21

The proportion of the population that is saved

Question 22

What does it mean when we say that EBV is an “unbiased” estimate of true breeding value

Answer 22

As we add more info for calculating that EBV, it is equally likely to increase as it is to decrease

Question 23

Which selection method is used by breed associations

Answer 23

BLUP (Best Linear Unbiased Prediction)

Question 24

Why is BLUP used instead of selection index

Answer 24

• 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

Question 25

Why are large scale genetic evaluations more often used on sire summaries than on dam summaries

Answer 25

Because 1 sire will have more effect on the herd than will 1 dam