An Sci 361 1st Edition Lecture 13 Outline of Last Lecture I. Genetic Model for Polygenic TraitsII. Basic Genetic Modela. EquationIII. Genetic Valuea. Equationb. Breeding Value i. Calculationc. Gene Combination Value i. CalculationIV. Use of Breeding ValueOutline of Current Lecture I. InbreedingII. SelfingIII. Consequences of Increased Homozygositya. Prepotencyb. Expressionc. Inbreeding DepressionIV. Inbreeding Depressiona. MeasuringCurrent LectureInbreeding- The mating of relatives- The mating of individuals more closely related than the average of the populationSelfingThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The mating of an individual with itself, is the most extreme form of inbreeding- Expected Increase in the Proportion of Homozygous Loci from Intensive InbreedingConsequences of increased homozygosity from inbreeding- 1. Prepotency - ability of an individual to produce progeny whose performance is especially like its own or is especially uniformo Example: Inbred: AABbCCdd- Types of gametes: ABCd, AbCd Noninbred: AaBbCCDd- Types of gametes: ABCD, ABCd, AbCD, AbCd, aBCD, aBCd, abCD, abCd- 2. Expression of deleterious recessive alleles with major effects - increased incidence of genetic defects- 3. Inbreeding depression - reduced performance in inbred animals for polygenic traitsWhy inbreeding depression?- Recessive alleles often result in lower performance than dominant alleles- Recessive alleles have maximum expression when they are homozygous- Inbreeding increases the proportion of loci with homozygous recessive alleles- Therefore, inbreeding results in lowered performance (inbreeding depression)- Inbreeding depression results from a loss in gene combination value caused by homozygous recessive loci replacing heterozygous loci at loci where some type of dominance exists.- Types of dominance and amount of decreased performance expected from inbreeding:o Overdominance - greatest inbreeding depressiono Complete dominanceo Partial dominanceo No dominance - no inbreeding depressionInbreeding Depression tends to be- Greatest for survival and reproduction traits o (e.g., disease resistance, conception rate)- Intermediate for production traitso (e.g., growth rate, milk production)- Lowest for product quality and conformation traits o (e.g., % milk protein, egg size, height)- Traits that show large inbreeding depression effects are those traits in which dominance effects (GCV) are relatively more important than individual additive gene effects (BV) in determining genotypic and phenotypic value. - These are the same traits that tend to have low heritability’s.Measuring Inbreeding- Fx quantifies the level of inbreeding.- Fx = the probability that both alleles of a pair (within a locus) are identical by descent (IBD) = the probability that both alleles of the pair are exact copies of a gene possessed by an ancestor.- Identical by descent calculation (Fx)- Fx for individuals from different matings:o Parents o Fx of offspringo sire x daughter o 0.25o son x dam o 0.25o full-sibs o 0.25o half-sibs o 0.125- Fx is the proportion of loci homozygous due to being inbred not the total proportion of homozygous loci.- Fx is a measure of the increased homozygosity above a non-inbred individual in the samepopulation.- Linebreeding: A form of inbreeding where a high degree of relationship is maintained to an important ancestor.- Prospector – a popular inbred line of Hereford cattle developed by Colorado State