Genetics Flashcards
Bio review
-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
Alleles and gene action
-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
Gene Combinations
-possible combinations of mating homozygous short-haired tom to heterozygous queen
-short hair is dominant
Type of gene action (incomplete)
Incomplete dominance
-Heterozygote is intermediate of the two homozygotes
-R-“dominant”
-r-“recessive”
-other: stress gene in swine
Types of gene action (codominance)
Codominance
-Heterozygote express both alleles
-Shorthorn cattle coat color
-Often denoted by X, X’
Overdominance
-Heterozygote is superior to either homozygote
-Usually associated with fitness or survivability
-often what we get with heterosis
Epistatic gene actions
-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
Gene Action - Sex influence traits
-Autosome=all chromosomes but the sex chromosomes
-sex chromosomes= mammals, XX=female, XY=male. =Birds, ZZ=male, ZW=female
Gene Action- Sex linked inheritance
-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
Gene Action- Sex limited traits
-Genes transmitted by both sexes (influenced by both chromosomes), but only expressed in one sex
-Ex) lactation, egg-laying
Traits
-observable or measurable characteristics
-height
-eye color
-hair color
Phenotype
-observed category or level of performance
-what you see
-5ft 4in
-Blue
-Blonds
Types of Traits
How many genes affect the trait?
-A few=monogenic (think Mendel)
-Many=polygenic (animal breeding)
Polygenic Traits
How is trait evaluated?
-Defined categories=Qualitative
-Continuous spectrum= Quantitative
-Often, monogenic traits are qualitative
Qualitative Traits
-Coat color
-Udder score, vulva score, foot and leg score
-puppies, kittens in a litter
Quantitative Traits
-continuous spectrum
-objectively measured
-carcass data, weight related measures, muscle ultrasound, running speed, methane emissions
Genotypes
The genes an animal possesses (DNA)
Phenotype =
Genotype + Environment
Heritability
-degree of phenotypic variation that is due to genetics
-Lower=less responsive to selective breeding and slower the genetic progress
Low and High Heritability
-Low~ phenotype = genetics + ENVIRONMENT
-high~ phenotype =GENETICS + environment
Genetic Change
-Mutation
-Migration (all white sheep and add a black one)
-Drift (one white and most brown move to all brown bunnies)
-Selection
Genetic Improvement
-goal of breeding is to improve populations, not individuals
-Breeding value= value of that animal as a parent
Genetic Improvement: Ways to make genetic change
-selection: which animals reproduce
-Mating: which males to which females
Genetic Improvement: Breeding Objective/Goal for breeding program
-Best animal for production system
-beef producer increasing profit when selling calves at weaning
-Sheep producer increasing profit from selling meat to ethnic market
Genetic Improvement: Expected progeny difference (EPD)
-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)
Mating systems: Inbreeding
-mate related animals
-Increase homozygosity, uniformity
-reduced performance and survivability
Mating System: Linebreeding
-form of inbreeding
-maximize relationship to a superior ancestor
-minimize inbreeding
-swine, poultry, horses
Mating System: Crossbreeding
-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
Heterosis example
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
Which mating system has most complementarity?
1.Angus x Hereford
2.Angus x Charolais
3.Yorkshire x Landrace
4.Duroc x Hampshire
Angus x Charolais because Angus is a maternal breed and Charolais are a terminal breed.
