ADSC 2010 Lecture 20Outline of Last Lecture I. MitosisII. MeiosisIII. GametogenesisA. SpermatogenesisB. OogenesisIV. Genetic Life CycleV. Gene locusVI. Father of GeneticsA. Gregor Mendel B. Two types of inherited traitsVII. InheritanceVIII. Multiple Allele’s Outline of Current Lecture I. Inheritance ContinuedA. Co-dominanceB. EpistasisC. Over DominanceD. HeterosisII. Improving Quantitative TraitsA. Two Basic Methods1. Selectiona. Methods of Selectionb. Selection Tools2. Mating or Breeding Systemsa. Breeding Valuei. Transmitting Ability1. Expected Progeny Difference (EPD)2. Predicted transmitting Ability (PTA)Current Lecture: I. Inheritance ContinuedA. Co-dominance: neither alleles completely cover the other, this the phenotype is amixture or blendingEx: Coat color of shorthornR: RED W:WHITE- RR: Red- WW: WHITE- RW: ROAN!B. Epistasis: a gene or gene pair masks (or controls) the expression of another non-allelic genetic pairEx: Albinoism in catsC: Color c: AlbinoB: Black b: brown- CC or Cc then B allele determines color: Black or brown- cc then C allele = albinoC. Over Dominance: heterozygote is superior to either of the homozygotes D. Heterosis (Hybrid Vigor): performance of cross-bred offspring is superior to the average of the parents (due to over dominance) Ex: Beef Cattle cross of Brahman with Bos Taurus Breeds.Ex of Traits: milk production, growth traits, ***REPRODUCTION***Another Example: Weaning weight in cattleBreed A: avg. ww = 540# avg.: 550#Breed B: avg. ww = 560# Heterosis amount: 30#A x B: avg. ww = 580#- Absolute heterosis: 30#- % Heterosis: 30# / 550# = ~5.5%II. Improving Quantitative TraitsB. Two Basic Methods for improving traits:1. Selection: choosing animals to be parents and source of genetic material- Selection changes the allelic “frequency” of a gene in the populationa. Methods of Selection- Single Trait Selection: make greatest change- Tandem Selection: select for a trait until some desired level is reached, then select for another trait- Independent Culling Level: set minimum standards for a trait and cull animals for that [cow: reproduction/calving]** Normally cow is best in other traits though…- Selection Index: combine traits into one value, based on their economic importance and level of genetic variationb. Selection Tools- Heritability: phenotype variation passed on through generationsH2 = VphenotypeVphenotype = Vgenotype + Venvironment- Appearance: Eliminate physical abnormalities Select for certain conformation- Pedigree: record of ancestry (family tree) Identifies lines that excel in traits- Family Selection: based on performance- Individual performance Records Trait has to be moderately to highly heritable- Progeny Testing: evaluation of an individual based on offspring (Takes a long period of time)- Genotyping ***Selection is trying to develop “Breeding Value”2. Mating or Breeding Systemsa. Breeding Value: measure of genetic valuei. Transmitting Ability: BV / 2 : amount an individual can contribute to offspring1. Expected Progeny Difference (EPD): beef, swine, some sheep, some horses2. Predicted transmitting Ability (PTA): more for dairy cattle Based on records from:o Individualo Pedigreeo
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