Breeding and Genetics 101. Understanding Breeds Outline What's the “Best” animal –Traits, Genotypes, Phenotypes Genes, Chromosomes and Genotypes –Dominance

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  • Breeding and Genetics 101

  • Understanding Breeds

  • OutlineWhat's the Best animalTraits, Genotypes, PhenotypesGenes, Chromosomes and GenotypesDominance and EpistasisSimply inherited vs. polygenic traitsStatistics and Their Role in Animal Breeding.Variation, Heritability, Genetic EvaluationHybrid Vigor/HeterosisThe Genetic ModelBreeding Value, Producing Ability

  • What's the BestAnimals are usually characterized in terms of appearance or performance or a combination of both.Traits Any observable or measurable characteristic of an animal.Coat colorMusclingWeaning WeightMarblingTemperment

  • Traits and PhenotypeTraits do not describe an individual.A red calf has weighted 576 lbs at weaning.Phenotype an observed category or level of performance for a trait.Red and 576 are phenotypes for coat color and weaning wt

  • What Determines Phenotype?P = G + EGenotype the genetic makeup of an animalEnvironmental Effects the effect of an external (non-genetic) factor has on phenotype

  • G x E Interaction

  • Genetics to GenesDNA deoxyribonucleic acidGenetic code of 4 basesChromosome a long strand of DNA, present in cell nucleus.Cattle have 30 pairsHumans have 23 pairsDogs have 39 pairsGene the basic unit of inheritance.Consists of DNA at a specific region on a chromosomeAllele alternate forms of a gene

  • DNA

  • HetrozygosityHomozygous posessing two copies of the same allele for a particular locusHeterozygous having two different alleles for a particular locus

  • DominanceDominant Allele - when present will override expression of any other allele for that traitRecessive Allele can only be expressed when both recessive copies of the allele are present for a particular trait

  • Punnett SquareHomozygous HornedHomozygous Polled100% Polled


  • Punnett SquareHeterozygous PolledHetrozygous Polled75% Polled


  • Punnett SquareHeterozygous polledHomozygous Horned50% Polled


  • Gene InteractionEpistasis An interaction among different loci such that the expression of one gene depends on another

  • Epistasis100% Black Coat Partial Diluted = GreyAngus





  • EpistasisA x C





  • Simple and Polygenic TraitsSimply inherited trait a trait that is affected by only one genePolygentic trait a trait affected by many genes, no single gene having an overriding influence

  • StatisticsMean the averageVariation differences among individuals within a populationVariance is the measure of variationCovariation is how two traits vary together

  • Variation and CovariationVariation - Good or Bad?Bad adds to inconsistencyGood Allows for increase selection efficiencyMeasured as varianceCovariation Good or Bad?Good allows for one trait to indicate anotherBad negative trait may be coupled with a positiveMeasured as covarianceCorrelation is the square root of covariance

  • Breeding ValuePart of the animals genotypic value that is due to transmittable gene effectsThe value of a parents genes to its progenys performanceNot all of the genotypic value is heritableAn EPD is the expected breeding value (EBV)

  • HeritabilityMany ways to look at it:The extent that the difference we observe in animal performance are due to inheritance.A measure of the strength of the relationship between performance (phenotypic values) and breeding values for a trait.It is a measure of correlation between breeding value and phenotype

  • Heritability Estimates

    Traith2Calving interval.05Birth Weight.40Weaning Weight.30Mature Weight.40Feed Conversion.40Scrotal Circumference.50Backfat Thickness.40Marbling Score.35

  • Heritability and SelectionHeritability is critical to selectionThe objective is to choose the animals with the best breeding values to become parentsTo do this we need the best info available, in most cases phenotype is usedSo the strength of relationship between phenotype and breeding values is very important

  • Genetic ModelRemember P = G + E?Lets expand that to:P = BV + GCV + EGCV = Gene Combination valueIncludes Epistatic effects and heterorsis

  • HeterosisAn increase in performance of hybrids over that of purebreds. Also caller Hybrid VigorResults in increased heterozygosityHereford 500 lb wwt averageAngus 500 lb wwt averageH x A 525 lb wwt average

  • HeterosisMore noticeable improvement in reproductive traitsLow heritability traitsHeterosis effects are not heritable, must be created every generation

  • Genetic ModelP = BV + GCV + EThe only heritable portion of this is BVAll national cattle evaluation programs center on prediction of BV (EBV)

  • Questions