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UGA ADSC 2010 - Mating Systems
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ADSC 2010 Lecture 21Outline of Last 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)Outline of Current Lecture I. Mating Systems1. Radom Mating2. Inbreeding3. Outbreedinga. Relationship of heritability and heterosis for different traitsb. How do we combine selection and mating systems?II. Crossbreeding Systems1. Two Breed Terminal Cross2. Two Breed Rotational Cross3. Three Breed Rotational CrossCurrent Lecture: - Requirements that make genetic progress1. Trait must be heritable2. Must be variation in population- Problems cloning- Genetic process = h2 x SD- H2: heritability- SD: selection pressure- difference between the average of the “individuals selected for mating” and the population - Ex: BackfatBF x = 0.8Boar A 0.4in 0.5in h2 = 0.5Boar B 0.6in SD= -0.3in (0.5-0.8)GENETIC PROCESS = 0.5x – 0.3 = -0.15in Population if all come from A and B will have .65in (go down .5in avg (x))I. Mating Systems- Organized manner of mating the “selected animals”1. Random mating- no selection2. Inbreeding- mating of animals that are more closely related than the average of the population- Line breeding: concentrate the genotype of one superior animal Mother to grandson.  Father to granddaughter Reduce genetic variation – look like one another  Cattle: certain lines selected Negative: issue with ?- Inbreeding depression – reduction of genetic variability and thus reduced vigor and fertility3. Outbreeding- mating of animals that are less closely related than average of population (crossbreeding)Ex: Heterosis: **lowly heritable traits Duroc Boar (2.4lbs / day)XYorkshire Sow (1.8lbs / day)||VCross bred pigs (2.3lbs / day) - Absolutely heterosis: 2.3 – 2.1 = 0.2- % heterosis: 0.2 / 2.1 = .095 = 9.5% Predictive of Duroc and Yorkshire for the specific traitSteersCull heifersMarketHerd 1Bull breed AHerd 2Bull breed BReplacement femalesReplacement femalesSteersCull heifers- Complementarity- moving forward of genetics of crossbred parents that would maintain superiority of offspringEx: Angus into crossbreeds- genes for marbling into next generation**HIGHLY HERITABLE TRAITSa. Relationship of heritability and heterosis for different traitsTrait Heritability HeterosisCarcass High (.4 - .5) LowGrowth Med (.25 - .35) MedRepro Low (.1 - .2) High **Big influence of repro traits – environment**Carcass – genotype – lower role on environment** environment – also heterosis (big impact)b. How do we combine selection and mating systems?Suffolk (male) x (merino x rambouillet – female) Highest quality cross-bred heterosisMeat complem.****SELECTION PRESSURE ON MALE.II. Crossbreeding Systems1. Two Breed Terminal Cross- End when crosses- everything produced  marketBreed A Breed BProgeny AB Marketed- Advantages: simpleo Maximized heterosis (100%) ½ A & ½ B at every gene loci: a allele and b allele- Disadvantages: have to maintain purebred herdso No heterosis in femaleso Used by small producers in cattle2. Two Breed Rational Cross Always mating females to opposite breed of their siresUsed a lot in beef cattle- Ex: Angus & Hereford: black belay- Advantages:o Simpleo Produce Femaleso Heterosis dam- Disadvantages: o 2/3 of offspring have heterosis : 67% heterosis o 2 pastures needed 3. Three Breed Rotational CrossUsed in Deseret ranches in FL- Brangus, Simbrah, Braford (54,000 moms)- Advantages:o ~86% heterosiso Produce Femaleso Heterosis in dams- Disadvantages:o Large numbers neededo Multiple pasturesHerd 2Bull breed BHerd 1Bull breed AHerd 3Bull breed C14.5 % A28.5 % B57.0 % C57.0 % A14.5 % B28.5 % C28.5 % A57.0 % B14.5 % Co Labor


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UGA ADSC 2010 - Mating Systems

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