Introduction to Genetics Darrh Bullock University of Kentucky
The Model Trait = Genetics + Environment
Genetics Additive Predictable effects that get passed from generation to generation Non-Additive Primarily dominance and genetic interactions Influenced by how genes match up
Crossbreeding
Why Crossbreed? Heterosis Advantage a crossbred has over the average of the parent breeds Due to non-additive genetics Breed Complementarity Matching breeds to fit each other Matching breeds to fit the environment
Selection
Types of Traits Qualitative Quantitative
Qualitative Traits Usually controlled by one pair of genes Usually limited impact by environment Most that we deal with have simple inheritance
Dominance/Recessive/Carriers Black (B) is dominant to red (b) Homozygous dominant (BB = Black) Heterozygous (Bb = Black) These animals are often referred to as carriers Homozygous recessive (bb = Red)
Mating a Carrier to a Carrier Black B b Black B b BB Black Bb Black Bb Black bb Red
Mating a Homozygous Dominant to a Carrier Black B B Black B b BB Black Bb Black BB Black Bb Black
Quantitative Traits Usually controlled by many gene pairs Usually a large impact by environment Interactions between genes and between genes and the environment Heritability the proportion of a trait that is controlled by additive gene action. The resemblance between parents and offspring, for a particular trait, due to genetics
Heritability Trait h 2 Reproduction Low Production Moderate Product High
Appearance History of Selection
Appearance
History of Selection Appearance Pedigree Information
History of Selection Appearance Pedigree Information Data Collection
Body Composition
History of Selection Appearance Pedigree Information Data Collection Ratios
Ratios Individual Weight X Contemporary Group Average 100
Contemporary Group 1 Physics Test Score Ratio = 86
Contemporary Group 2 Physics Test Score Ratio = 116
History of Selection Appearance Pedigree Information Measurable Trait Ratios Breeding Value Pedigree and Phenotype
Expected Progeny Differences Physics Score EPDs 25 Points 15 Points 5 Points
Has Selection Worked? Genetic Trends All breeds show drastic changes in genetic merit of most traits. Indicate that simultaneous selection for antagonistic traits is possible.
Angus Genetic Trends
Genetic Evaluation Models Trait = Genetics + Environment Basic Statistical Model Phenotype = Genetic Merit + Environment Effects + Unexplained Variation
Genetic Evaluation Models Basic Model Phenotype Environment Effects Unexplained Variation = Genetic Merit
Genetic Evaluation Models Basic Model Phenotype Environment Effects = Genetic Merit + Unexplained Variation
Unexplained Variation Data Accuracy Zero
75 lbs 55 lbs 95 lbs Potential Genetic Merit of Gametes Produced by a Bull
Mendelian Sampling Cattle have 30 pairs of chromosome and a parent passes one from each pair to a progeny. How many genetically different gametes (sperm or eggs) can a parent produce given this sampling process? 1,073,741,824
55 lbs 75 lbs 35 lbs 95 lbs Comparing Gametes Produced by Bulls with Differing EPDs
Accuracy Yearling Weight Accuracy in Angus Bulls.10 relates to a possible change value of 15 lbs. 75 ± 15 = 60 to 90.90 relates to a possible change value of 2 lbs. 75 ± 2 = 73 to 77
Unexplained Variation Data Accuracy Zero
Selection Index Weights traits according to economic importance Allows comparison on single value Selection index = a 1 EPD 1 + a 2 EPD 2 +... + a k EPD k
Selection Index Selection index = a 1 MPV 1 + a 2 MVP 2 +... + a k MVP k Combined Selection index = a 1 MPV 1 + a 2 EPD 2 + a 3 MPV 3... + a k EPD k
Conclusions Crossbreeding is an essential part of every commercial beef operation Selection should be made on traits that economically impact your herd
Conclusions There are multiple tools to assist in making selection decisions. Visual EPDs Genomics Selection Indices