An Sci 361 1st Edition Lecture 17 Outline of Last Lecture I. Covariationa. Positiveb. Negativec. MeasuresII. Covariance’s and the Genetic ModelIII. RegressionOutline of Current Lecture I. Phenotypic Valuea. HeritabilityII. Heritabilitya. Traitsb. Usesc. What it isd. What it is note. How to increase itf. Narrow Senseg. Broad SenseIII. Genetic DifferencesCurrent LectureModel of Phenotypic Value- P = μ + G + E- P = μ + BV + GCV + Eo Where: BV = Breeding Value GCV = Gene Combination Value- Heritability o (h2) is a characteristic of a trait in a population. High h2: High (low) phenotypes tend to be associated with high (low) breeding values and vice versa.o Measures the strength of the relationship between phenotypes and breeding values of individuals within the population.I. Portion of phenotypic variance that is due to BV varianceThese 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.II. Regression of BV on PDifferent Traits – Different Heritability’s- High heritability (h2 > .35): o Indicates strong relationship between P and BVo Little environmental influenceo P is a relatively accurate predictor of BV Examples: Product quality and stature traits, e. g., milk fat %, milk protein %, back fat thickness, loin eye area, wool staple length, mature size, body conformation/type- Moderate heritability (0.15 < h2 < 0.35):o Examples: Production traits; e. g., milk yield, growth rate, juvenile body weights, egg production- Low heritability (h2 < .15):o Indicates weak relationship between P and BVo Strong environmental influenceo P is an inaccurate predictor of BV Examples: Reproduction, health, and survival traits- Uses of Heritabilityo Predict an individual’s BV from its own single phenotypic recordo Predicted portion of the difference between individuals that is due to their difference in BVo Measures the accuracy of the prediction of BV from a single phenotypic record on the individualHeritability IS- A measure of the strength of the relationship between performance (phenotypic values) and breeding values for a trait within a population – the degree to which a phenotype is predictive of the BV.Heritability is NOT- Ability of an animal to transmit its genes - All reproductively capable individuals have that ability- Percentage of genes transmitted to progeny - This is always 50% - A measure of the quality or value of genes transmitted - This is determined by BV and Mendelian samplingHow to increase heritability of a trait- Raise animals under a uniform environment so environmental variation is reduced- Measure the trait accurately- Mathematical adjustments for known environmental effectsNarrow Sense and Broad Sense Heritability- Heritability in the narrow sense (h2)o Relationship of P with BV)P(V)BV(Vh2- Heritability in the broad sense (H2)o Relationship of P with G [G = BV + GCV])P(V)GCV(V)BV(VH2How do we discover genetic differences/determine that a trait is heritable?- Differences among averages of large half-sib familieso Somatic cell score:  Lowest sires average 2.6; highest average 3.6o Calf mortality: Lowest sires average 1.1%; highest average 9.4%- Regression of offspring performance on parental performanceo Measures the portion of phenotypic differences among parents (e. g., sires) that are seen in [or literally transmitted to] their progeny performanceo A sire and his progeny have in common one-half of the sire’s breeding valueo Twice the regression of sire phenotype on progeny phenotype is an estimate of heritability o Requires hundreds of parent-offspring