Lecture 16 - Alleles And Inheritance (part 2)

Question 1

What are qualitative traits?

Answer 1

Traits that can be described but only measured subjectively

• categories
• coat color, horns

(Controlled by a relative small number of genes; simply-inherited traits)

Question 2

What are quantitative traits?

Answer 2

Numerically measured : continuous expression
- milk yield, litter size, mature weight

Controlled by many genes (polygenic)

Question 3

What are the differences between qualitative and quantitative traits?

Answer 3

Quantitative - greater environmental influence, variable heritability

Qualitative - less environmental influence, greater heritability

Question 4

What is heritability?

Answer 4

Proportion of phenotypic variation that van be passed to next generation

• measure of the strength of the relationship between phenotypes and breeding values
• not constant; vary across populations and over time

Question 5

How is heritability quantified?

Answer 5

A number between 0 and 1 (proportion)

• low heritability = 0 - 0.2 (example reproductive traits)
• moderate heritability = 0.2-0.4 (ex growth traits)
• high heritability = 0.4-0.6 (ex carcass merit traits)

Question 6

What is the influence of heritability on traits?

Answer 6

Low heritability -> no substantial change from generation to generation with selection

High heritability -> greater degree of change (can be selected for superiority

Question 7

What is genetic progress?

Answer 7

Selection differential x heritability

Question 8

What is selection differential?

Answer 8

The phenotypic advantage of animals selected to be parents over the population average

Question 9

What is the rate of genetic progress?

Answer 9

(Selection differential x heritability)/ generation interval

Question 10

What is the generation interval

Answer 10

Average time required to replace one generation with the next

Question 11

What are steps taken in mating systems to breed animals?

Answer 11

Selection : identify animals to breed

Mating : determine which selected males will be bred to which selected females

Question 12

What is random mating?

Answer 12

Selected animals mate at random

• mating of selected animals is not controlled

Question 13

What is inbreeding?

Answer 13

Mating of related animals (within a breed)

• purebreds
• to concentrate desired genes
• creates inbreeding depression

Question 14

What is line-breeding

Answer 14

• mating animals that have one common ancestor

(Mild form of inbreeding)

Question 15

What are some examples of line breeding and inbreeding?

Answer 15

Inbreeding : mating of sire to a daughter

Line-breeding : mating of a grand sire to a granddaughter

Question 16

What is outbreeding?

Answer 16

Mating of a relative that is not closely related

• opposite of inbreeding
• increase heterozygosity and decrease expression of deleterious recessive genes

Question 17

What is heterosis?

Answer 17

Hybrid vigor
- superiority of an out red animal

• inversely related to heritability

Question 18

What is breeding value?

Answer 18

Mating of individual with different but complementary breeding values