Genetics

Question 1

Bio review

Answer 1

-Animals are diploid= two copies of genetic material, one from each parent
-DNA organized into long, unbroken strands called chromosomes
-Gene: functional units within chromosomes, position of gene on chromosome=locus
-Genes usually have 2 alternate forms, called alleles

Question 2

Alleles and gene action

Answer 2

-alleles are considered dominant or recessive
-Homozygous=two alleles for a particular gene are identical
-Heterozygous-two alleles for a particular gene are different
-Dominance= simple dominance

Question 3

Gene Combinations

Answer 3

-possible combinations of mating homozygous short-haired tom to heterozygous queen
-short hair is dominant

Question 4

Type of gene action (incomplete)

Answer 4

Incomplete dominance
-Heterozygote is intermediate of the two homozygotes
-R-“dominant”
-r-“recessive”
-other: stress gene in swine

Question 5

Types of gene action (codominance)

Answer 5

Codominance
-Heterozygote express both alleles
-Shorthorn cattle coat color
-Often denoted by X, X’

Question 6

Overdominance

Answer 6

-Heterozygote is superior to either homozygote
-Usually associated with fitness or survivability
-often what we get with heterosis

Question 7

Epistatic gene actions

Answer 7

-epistatic = interaction of non-allelic gene
-Ex) coat color in Labrador Retrievers. Locus 1= coat color gene: Black(B)/chocolate(b). Locus 2= expression gene locus: yes(E)/(e)
-E/e gene influences B/b gene even though they are not alleles

Question 8

Gene Action - Sex influence traits

Answer 8

-Autosome=all chromosomes but the sex chromosomes
-sex chromosomes= mammals, XX=female, XY=male. =Birds, ZZ=male, ZW=female

Question 9

Gene Action- Sex linked inheritance

Answer 9

-X-chromosomes=larger and longer than Y
=Male portion of X that does not pair with Y
=These genes are sex-linked
-Usually, recessive
-red-green colorblindness, hemophilia
-Orange color in cats

Question 10

Gene Action- Sex limited traits

Answer 10

-Genes transmitted by both sexes (influenced by both chromosomes), but only expressed in one sex
-Ex) lactation, egg-laying

Question 11

Traits

Answer 11

-observable or measurable characteristics
-height
-eye color
-hair color

Question 12

Phenotype

Answer 12

-observed category or level of performance
-what you see
-5ft 4in
-Blue
-Blonds

Question 13

Types of Traits

Answer 13

How many genes affect the trait?
-A few=monogenic (think Mendel)
-Many=polygenic (animal breeding)

Question 14

Polygenic Traits

Answer 14

How is trait evaluated?
-Defined categories=Qualitative
-Continuous spectrum= Quantitative
-Often, monogenic traits are qualitative

Question 15

Qualitative Traits

Answer 15

-Coat color
-Udder score, vulva score, foot and leg score
-puppies, kittens in a litter

Question 16

Quantitative Traits

Answer 16

-continuous spectrum
-objectively measured
-carcass data, weight related measures, muscle ultrasound, running speed, methane emissions

Question 17

Genotypes

Answer 17

The genes an animal possesses (DNA)

Question 18

Phenotype =

Answer 18

Genotype + Environment

Question 19

Heritability

Answer 19

-degree of phenotypic variation that is due to genetics
-Lower=less responsive to selective breeding and slower the genetic progress

Question 20

Low and High Heritability

Answer 20

-Low~ phenotype = genetics + ENVIRONMENT
-high~ phenotype =GENETICS + environment

Question 21

Genetic Change

Answer 21

-Mutation
-Migration (all white sheep and add a black one)
-Drift (one white and most brown move to all brown bunnies)
-Selection

Question 22

Genetic Improvement

Answer 22

-goal of breeding is to improve populations, not individuals
-Breeding value= value of that animal as a parent

Question 23

Genetic Improvement: Ways to make genetic change

Answer 23

-selection: which animals reproduce
-Mating: which males to which females

Question 24

Genetic Improvement: Breeding Objective/Goal for breeding program

Answer 24

-Best animal for production system
-beef producer increasing profit when selling calves at weaning
-Sheep producer increasing profit from selling meat to ethnic market

Question 25

Genetic Improvement: Expected progeny difference (EPD)

Answer 25

-difference in performance from expected progeny of a sire compared to the performance of progeny of an average sire
-Accuracy=level of confidence in EPD value (0-1.0)
-Used to COMPARE animals (either to each other or the breed average)

Question 26

Mating systems: Inbreeding

Answer 26

-mate related animals
-Increase homozygosity, uniformity
-reduced performance and survivability

Question 27

Mating System: Linebreeding

Answer 27

-form of inbreeding
-maximize relationship to a superior ancestor
-minimize inbreeding
-swine, poultry, horses

Question 28

Mating System: Crossbreeding

Answer 28

-less related individual’s mates
-often different breeds
-increased heterozygosity, performance
-Heterosis=hybrid vigor, superiority of crossbred relative to average of parent breeds
-Complementarity= mating breeds that excel at different traits to match strengths and weakness

Question 29

Heterosis example

Answer 29

Weaning weight in cattle
-weaning weight has 2% heterosis in beef cattle (in our example)
-Angus average 550lbs and Hereford average 500lbs so the average is 525lbs
-Angus x Hereford cross average 536lbs
-Main reason why we use crossbreeding

Question 30

Which mating system has most complementarity?
1.Angus x Hereford
2.Angus x Charolais
3.Yorkshire x Landrace
4.Duroc x Hampshire

Answer 30

Angus x Charolais because Angus is a maternal breed and Charolais are a terminal breed.