Introduction to Genetics - NCBA · Genetics Additive ... Basic Statistical Model Phenotype =...
Transcript of Introduction to Genetics - NCBA · Genetics Additive ... Basic Statistical Model Phenotype =...
Introduction to GeneticsDarrh Bullock
University of Kentucky
The Model
Trait = Genetics + EnvironmentTrait = Genetics + Environment
Genetics
AdditivePredictable effects that get passed from generation to generation
Non-AdditivePrimarily dominance and genetic interactionsInfluenced by how genes match up
Crossbreeding
Why Crossbreed?
HeterosisAdvantage a crossbred has over the average of the parent breedsDue to non-additive genetics
Breed ComplementarityMatching breeds to fit each otherMatching breeds to fit the environment
Selection
Types of Traits
QualitativeQuantitative
Qualitative Traits
Usually controlled by one pair of genesUsually limited impact by environmentMost 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
B b
B BBBlack
BbBlack
b BbBlack
bbRed
♂♂
♀♀BlackBlack
BlackBlack
Mating a Homozygous Dominant to a Carrier
B B
B BBBlack
BBBlack
b BbBlack
BbBlack
♂♂
♀♀BlackBlack
BlackBlack
Quantitative TraitsUsually controlled by many gene pairsUsually a large impact by environmentInteractions between genes and between genes and the environmentHeritability – 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 h2
Reproduction
Production
Product
Low
Moderate
High
History of Selection
Appearance
Appearance
History of Selection
Appearance Pedigree Information
History of Selection
Appearance Pedigree InformationData Collection
Body Composition
History of Selection
Appearance Pedigree InformationData CollectionRatios
Ratios
Individual Weight Individual Weight
Contemporary Group AverageContemporary Group AverageX 100X 100
Contemporary Group 1Physics Test Score
Ratio = 86Ratio = 86
Contemporary Group 2Physics Test Score
Ratio = 116Ratio = 116
History of Selection
Appearance Pedigree InformationMeasurable TraitRatiosBreeding Value
Pedigree and Phenotype
Expected Progeny DifferencesPhysics Score EPDsPhysics Score EPDs
25 Points25 Points
15 Points15 Points
5 Points5 Points
Has Selection Worked?
Genetic TrendsAll 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
Basic Statistical Model
Phenotype = Genetic Merit +
Environment Effects + Unexplained Variation
Trait = Genetics + EnvironmentTrait = Genetics + Environment
Genetic Evaluation ModelsBasic Model
Phenotype –Environment Effects –
Unexplained Variation =
Genetic Merit
Genetic Evaluation ModelsBasic Model
Phenotype –Environment Effects =
Genetic Merit + Unexplained Variation
Unexplained Variation
ZeroZero
DataData AccuracyAccuracy
Potential Genetic Merit of Gametes Produced by a Bull
95 lbs95 lbs55 lbs55 lbs
75 lbs75 lbs
Mendelian Sampling
Cattle have 30 pairs of chromosome and a parent passes Cattle have 30 pairs of chromosome and a parent passes one from each pair one from each pair to a progeny.to a progeny.
1,073,741,8241,073,741,824
How many genetically different gametes (sperm or eggs) How many genetically different gametes (sperm or eggs) can a parent produce given this sampling process? can a parent produce given this sampling process?
Comparing Gametes Produced by Bulls with Differing EPDs
55 lbs55 lbs
95 lbs95 lbs35 lbs35 lbs
75 lbs75 lbs
AccuracyYearling 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
ZeroZero
DataData AccuracyAccuracy
Selection Index
Weights traits according to economic importanceAllows comparison on single valueSelection index
= a1EPD1 + a2EPD2 + . . . + akEPDk
Selection Index
Selection index = a1MPV1 + a2MVP2 + . . . + akMVPk
Combined Selection index = a1MPV1 + a2EPD2 + a3MPV3. . . +
akEPDk
ConclusionsConclusions
Crossbreeding is an essential part of every commercial beef operation Selection should be made on traits that economically impact your herd
ConclusionsConclusions
There are multiple tools to assist in making selection decisions.
VisualEPDsGenomicsSelection Indices