ADSC 2010 Lecture 20 Outline of Last Lecture I Mitosis II Meiosis III Gametogenesis A Spermatogenesis B Oogenesis IV Genetic Life Cycle V Gene locus VI Father of Genetics A Gregor Mendel B Two types of inherited traits VII Inheritance VIII Multiple Allele s Outline of Current Lecture I Inheritance Continued A Co dominance B Epistasis C Over Dominance D Heterosis II Improving Quantitative Traits A Two Basic Methods 1 Selection a Methods of Selection b Selection Tools 2 Mating or Breeding Systems a Breeding Value i Transmitting Ability 1 Expected Progeny Difference EPD 2 Predicted transmitting Ability PTA Current Lecture I Inheritance Continued II A Co dominance neither alleles completely cover the other this the phenotype is a mixture or blending Ex Coat color of shorthorn R RED W WHITE RR Red WW WHITE RW ROAN B Epistasis a gene or gene pair masks or controls the expression of another nonallelic genetic pair Ex Albinoism in cats C Color c Albino B Black b brown CC or Cc then B allele determines color Black or brown cc then C allele albino C 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 cattle Breed 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 Improving Quantitative Traits B 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 population a 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 variation b Selection Tools Heritability phenotype variation passed on through generations 2 H Vphenotype Vphenotype 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 Systems a Breeding Value measure of genetic value i Transmitting Ability BV 2 amount an individual can contribute to offspring 1 Expected Progeny Difference EPD beef swine some sheep some horses 2 Predicted transmitting Ability PTA more for dairy cattle Based on records from o Individual o Pedigree o Progeny
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