Genetic selection tools in the genomics era
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Genetic Selection Tools in the Genomics Era. Curt Van Tassell, PhD Bovine Functional Genomics Laboratory & Animal Improvement Programs Laboratory Beltsville, MD. Outline. Background Genetic Evaluations Quantitative Genetics Genomics Integrating Genetics and Genomics Case Study: DGAT1

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Genetic selection tools in the genomics era

Genetic Selection Tools in the Genomics Era

Curt Van Tassell, PhD

Bovine Functional Genomics Laboratory & Animal Improvement Programs Laboratory

Beltsville, MD


Outline

Outline

  • Background

    • Genetic Evaluations

    • Quantitative Genetics

    • Genomics

  • Integrating Genetics and Genomics

  • Case Study: DGAT1

  • Tangent: Animal Identification

  • Crystal Ball

  • Conclusions


Background

Background

  • Bovine Functional Genomics Laboratory (BFGL)

    • Structural and functional genomics of cattle

    • Emphasis on health and productivity

    • Bioinformatics (storage and use of genomic data)

  • Animal Improvement Programs Laboratory (AIPL)

    • “Traditional” genetic improvement of dairy cattle

    • Increasing emphasis on animal health and reproduction


Traditional selection programs

Traditional Selection Programs

  • Estimate genetic merit for animals in a population

  • Select superior animals as parents of future generations


Genetic evaluation system

Genetic Evaluation System

  • Traditional selection has been very effective for many economically important traits

  • Example: Milk yield

    • Moderately heritable

    • ~30 million animals evaluated 4x/yr

    • Uses ~70 million lactation records

    • Includes ~300 million test-day records

    • Genetic improvement is near theoretical expectation


Dairy cattle genetics success

2000

Cows

Bulls

0

-2000

BV Milk

-4000

-6000

1960

1970

1980

1990

2000

Year of Birth

Dairy Cattle Genetics Success


Dairy cattle genetics industry cooperation

Dairy Cattle Genetics Industry Cooperation


Genomics introduction

Genomics - Introduction

  • Traditional dairy cattle breeding has assumed that an infinite number of genes each with very small effect control most traits of interest

  • Logical to expect some “major” genes with large effect; these genes are usually called quantitative trait loci (QTL)

  • The QTL locations are unknown!

  • Genetic markers can provide information about QTL


Genetic markers

Polymorphism

“poly”= many“morph”= form

General

population

94%

Single nucleotide

polymorphism

(SNP)

6%

Genetic Markers

  • Allow inheritance of a region of the genome to be followed across generations

  • Single nucleotide polymorphisms (SNiP) are the markers of the future!

  • Need lots!

    • 3 million in the genome

    • 10,000 initial goal


Application of genetic markers

Application of Genetic Markers

  • Identify genetic markers or polymorphisms in genes that are associated with changes in genetic merit

  • Use marker assisted selection (MAS) or gene assisted selection (GAS) to make selection decisions before phenotypes are available

  • Adjust genetic merit for markers or genes in the genetic evaluation system


Genetic selection tools in the genomics era

QTL Identification

DNA

Genetic

Merit

Data


Qtl identification and marker assisted selection

1.7

3.5

-0.1

0.7

-2.5

-6.2

QTL Identification and Marker Assisted Selection

Compare Genetic

Merit


Gene assisted selection

Gene Assisted Selection


Marker or gene assisted selection

Marker or Gene Assisted Selection

  • Largest benefits are for traits that:

    • have low heritability, i.e., traits where genetics contribute a small fraction of observed variation (e.g., disease resistance and fertility)

    • are difficult or expensive to measure (e.g., parasite resistance )

    • cannot be measured selection decision needs to be made (e.g., milk yield and carcass characteristics)

  • Evolution in traditional selection program by improving estimation of genetic merit


Example dgat1

Example: DGAT1

  • DGAT1: diacylglycerol acyltransferase

    • Enzyme involved in fat sythesis

    • Identified using

      • Genetic marker data

      • Model organism (mouse) gene function information

      • Cattle sequence verified candidate gene


Dgat1

DGAT1

  • Two forms of the gene in cattle

    • M = high milk (low fat) form of gene

    • F = high fat (low milk) form gene

  • BFGL scientists decided to characterize the gene in North American population

    • Over 3300 animals genotyped for DGAT1 SNP

    • Approximately 2900 genotypes verified and used in these analyses


Dgat1 average differences in daughters of bulls

DGAT1 – Average Differencesin Daughters of Bulls


Dgat1 genotypic frequencies

DGAT1 Genotypic Frequencies


Integrating genomics results

Integrating Genomics Results

  • Genes will likely account for a fraction of the total genetic variation

  • Cannot select solely on gene tests!!


Integrating genomic data an ideal situation

Integrating Genomic Data:An Ideal Situation!

Bull PTA


Integrating genomic data the dgat1 nm situation

MM

FF

Integrating Genomic Data: The DGAT1 NM$ Situation!

Bull PTA NM$


Integrating genomic data the dgat1 fat situation

MM

FF

Integrating Genomic Data: The DGAT1 Fat Situation!

Bull PTA Fat


Integrating genomics results1

Integrating Genomics Results

  • Combine information

    • Ideally would incorporate genomic data into genetic evaluation system

  • Adjust PTA??

    • Don’t adjust well proven animals (it’s in there!!)

    • Adjust parent average for flush mates

      • Progeny have identical parent averages

  • Adjusting other PTA is non-trivial!


Integrating genomic data another view of dgat1 nm

Integrating Genomic Data: Another view of DGAT1 NM$!

MM

FF

Bull PTA NM$


And it really works

And it Really Works!

  • Recent German study evaluated impact on adjusting historic parent averages (PA) for DGAT1 and evaluated impact of predictability of future evaluations

  • Correlations of original PA with eventual PTA for milk were 45%

  • Correlations of adjusted PA with eventual PTA for milk were 55% (10% gain)

  • Incorporation of genomic data will result in increased stability of evaluations


Genetic evaluations limitations

Genetic Evaluations - Limitations

  • Slow!

    • Progeny testing for production traits take 3 to 4 years from insemination

    • A bull will be at least 5 years old before his first evaluation is available

  • Expensive!

    • Progeny testing costs $25,000 per bull

    • Only 1 in 8 to 10 bulls graduate from progeny test

    • At least $200,000 invested in each active bull!!


Genetic evaluations genomics enhancements

Genetic Evaluations:Genomics Enhancements

  • Faster

    • Use of gene and marker tests allow preliminary selection decisions beyond parent average before performance and progeny test data are available

  • Cheaper

    • Improved selection decisions should result in higher graduation rates or enhanced genetic improvement


How do we get there

How do we get there

  • Increase number of genetic markers

  • Continue QTL discovery for MAS/GAS

  • Better characterize the genome

    • Compare genome to well characterized human and mouse genome


Bovine genome sequence

Bovine Genome Sequence


Bovine genome sequence1

Bovine Genome Sequence

  • Inbred Hereford is primary animal being sequenced

  • Genome size is similar to humans

  • Sequencing about half completed

  • First assembly released yesterday!!

    • 2.3 of 2.8 billion base pairs

    • 84% coverage

L1 Dominette 01449


Bovine genome sequence2

Bovine Genome Sequence

  • Six breeds selected for low level sequencing

  • Holstein and Jersey cows represent dairy breeds

  • Useful for SNP marker development

  • Expect 3 million SNPs in the genome

  • Preliminary goal is to characterize 10,000

Wa-Del RC Blckstr Martha-ET

Mason Berretta Jenetta


Genomic tools for parentage verification

Genomic Tools for Parentage Verification

  • Low-cost high-throughput SNP marker tests would facilitate parentage verification and traceability

  • $10 to $20 per sample seems to be a common break point

  • Progeny test herds would likely be early adopters

    • Support from studs?

  • Results in increased stability on first proofs?

    • Nearly impossible to make mistake on parentage

    • Punished on second crop proofs?

  • With widespread implementation

    • Increase effective heritability

    • Decrease evaluation variability

    • Enhanced genetic improvement


Crystal ball wishful thinking

Crystal Ball (Wishful Thinking?)

  • Large number of validated genetic tests available

  • Large amounts of marker and gene data publicly available

  • Genomic data incorporated into genetic evaluation

  • Management decisions facilitated by genomics data


Considerations in genomic tests

Considerations in Genomic Tests

  • How big is the effect?

    • Traits of interest, economic index (NM$, TPI, PTI)

    • How many genetic standard deviation units?

  • Has this been validated by a sufficiently large independent study?

  • What correlated response is expected & observed?

  • What are allele frequencies?

  • What is the value of this test?

    • not simple to answer


Conclusions

Conclusions

  • Genomics is enhancing genetic improvement

  • DGAT1 has large impacts on milk, fat, protein, SCS

  • Genetic tests need to be weighted appropriately for optimal selection decisions

  • Genomic tools will be extremely powerful for parentage verification and traceability

    • Could impact genetic evaluations


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