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