In-Service: Animal Breeding and Genetics

Dr. Alan FaheyMarch 24th 2011

NCE-MSTL, University of Limerick

Contact Information

• alan.fahey@ucd.ie

• 01-7166248

• Room 238 Vet Sciences Centre, School of Agriculture, Food Science, and Veterinary Medicine, UCD, Belfield, Dublin 4.

Topics Covered

• Variation• Dominance• Inbreeding and Crossbreeding• Progeny and Performance Testing• Problem based learning sessions• How to use an AI Catalogue

Variation

Variation LCH 2006 7(a) iii

• Differences among individuals within a population

• Tells us about the uniformity of the population

• Variation exists for performance, genetic, and environmental components

Continuous Variation DiscreteVariation

Quantitative traits have continuous variation

Quantitative traits are controlled by many genes

Each gene has a small effect

Qualitative traits have discrete variation

Qualitative traits are controlled by a single gene

Single gene has a large effect

Why is Variation Important?

• Variation is the source of genetic change

• If there is little genetic variation then it is difficult to find an individuals with better genetic potential

Why is Variation Important?

• Variation is the source of genetic change

• If there is little genetic variation then it is difficult to find an individuals with better genetic potential

Dominance

Dominance: Glossary• Allele - Alternate forms of genes. Genes occur in

pairs in body cells, one gene of a pair may have one effect and another gene of that same pair (allele) may have a different effect on the same trait.

• Heterozygote – one dominant and one recessive allele

• Homozygote – both alleles are either dominant or recessive

• Genotype – combination of genes for a trait

Complete Dominance (2000 Q7d)

Kk, kk (wrinkled) KK (smooth)

The expression of the heterozygote is identical to the expression of the homozygous dominant genotype

Ss, ss (non-starchy) SS (starchy)

Cross: KKSS x KkSs

Alleles: K K S S x K k S s

F1 Genotype: KKSS;KKSs;KkSS ;KkSs

F1 Phenotype: All smooth and starchy

Partial Dominance

YY yy

The expression of the heterozygote is intermediate to the expression of the homozygous dominant genotype and more closely resembles the homozygous dominant genotype

Yellow Green

Yy

No Dominance

rr RR

The expression of the heterozygote is exactly midway to the expression of the homozygous genotypes

White Roan

Rr

Red

Shorthorn Cattle

Cross: Rr x Rr (Roan x Roan)

Alleles: R r x R r

F1 Genotype: RR; Rr ;Rr ; rr

F1 Phenotype: red; roan;roan; white

Over Dominance

Yy yy

The expression of the heterozygote is outside the range defined by the homozygous genotypes and most closely resembles the expression of the homozygous dominant genotypes

Yellow Green

YY

Inbreeding and Crossbreeding

Inbreeding v Crossbreeding2007 HL 7(a) i

• Recessive – an allele whose phenotype is masked when the dominant allele is present

• Inbreeding depression - loss in performance due to inbreeding

• Locus – the location of a gene on a chromosome

• Related animals have more genes in common

• Animals of outstanding genetic merit are likely to have relatives that have above average genetic merit

Inbreeding

www.eurogeneaiservices.com

C

C

• Related animals also have more unfavourable genes in common

• Some recessive genes cause genetic diseases, or adversely affect reproduction, survival or fitness of animals

• Only cause problems in animals that carry two copies of the gene - homozygous recessive animals

Inbreeding

• Matings between related animals are more likely to produce offspring that are homozygous for these genes than matings between unrelated animals

• Whenever selection is practiced in a closed population (eg breed, closed herd) over a long period of time, there is an gradual increase in inbreeding

• This increase is cumulative and inevitable

Inbreeding

• Inbreeding depression– Reverse of hybrid vigour– A decrease in performance of inbreds (fertility,

survivability)

• Line-breeding– Dramatic form of inbreeding– Mating of individuals within a particular line– Designed to maintain a substantial degree of relationship

to a highly regarded ancestor without causing high levels of inbreeding

– Many breeds were formed by line-breeding e.g. father-daughter or mother-son matings

Inbreeding

• Why inbreed?1) Increase in uniformity

2) Create opportunity for hybrid vigour (in crosses of inbreds

3) To identify deleterious recessive alleles in population

4) Necessary for breeders of registered purebreds as matings to non-purebred ineligible for registration

Inbreeding

Inbreeding % in Irish Cattle

Charolais (-∆-), Limousin (--), Hereford (-•-), Angus (--), Simmental(- -), and Holstein-Friesian (-₀-) breeds across year of birth.▲

Mc Parland et al., 2007

Inbreeding DepressionInbreeding Class (%)

Milk Yield (kg) Fat Yield (kg) Protein Yield (kg)

Somatic Cell Score

0 <F ≤ 6.25 6.8 1.9 0.2 7.6

6.25 <F ≤ 12.5 -47.5 -0.9 -1.9 10.8

12.5 <F ≤ 25 -160.9 -6.0 -4.8 2.4

> 25 -172.5 -4.8 -5.9 14.6

Mc Parland et al., 2007

Crossbreeding• Mating of two non-related individuals from

different breeds• Breed A are homozygous recessive at the B

locus (bb)• Breed B are homozygous recessive at the B

locus (BB)• Crossing breed A and B lead to heterozygosity

at locus B (Bb)• Creates hybrid vigour (heterosis)

Hybrid Vigour= extra performance above mid-parent mean

Breed A A x B Breed B

Per

form

ance

Hybrid Vigour• Greatest in traits associated with reproduction,

survival and overall fitness

• Opposite of inbreeding depression

• Crossbreeding creates animals which are heterozygous at more loci

• Lower proportion of offspring are homozygous for recessive genes that adversely affect reproduction etc.

• Greater between genetically diverse breeds

Progeny Test

Performance v Progeny Testing2007 HL 7(a) ii

• Performance testing is carried on the individual animal e.g feed intake, growth

• This is carried out at a central location (one environment)

• This information is used to determine the genetic merit of the animal and its ancestors

Progeny Test

• A team of sires are mated to females in several herds

• Detailed phenotype information is recorded on all progeny

• This provides information on sires progeny across several environments

• This is used to calculate the genetic merit of the sire, dam, and progeny

Sire

Progeny Farm 1

Progeny Farm 2

Progeny Farm 3

Progeny Farm n

Phenotypes and Pedigree Stored in Database e.g ICBF and Sheep Ireland

A.I. Catalogues

Teaching resourcesGeneral Information• www.icbf.com• http://www.icbf.com/publications/glossaryatol.php (glossary)• http://www.icbf.com/publications/2008cattlestat.php (cattle statistics)• http://www.icbf.com/publications/index.php (publications)• www.sheep.ie• http://www.sheep.ie/publications/glossary.php (glossary)• http://www.sheep.ie/publications/referencedocs.php (publications)

Sheep Breed Societies• www.belclaresheep.com• www.charollaissheep.com• www.pedigreesheep.com• www.irishtexel.com • www.vendeensheep.ie• www.mayosheepproducers.com• www.suffolksheep.org

•

Teaching resources• Dairy Cattle

– www.irishshorthorns.com– www.ihfa.com– www.ukjerseys.com– www.brownswissusa.com

• Beef Cattle – www.aberdeen-angus.co.uk– www.irishangus.ie– www.ibbcs.com– www.aubrac.ie– www.irishblondedaquitaine.ie– www.charolais.ie– www.irishhereford.com– www.irishlimousin.com– www.irishpiemontesesociety.ie– http://www.irishsimmental.com/

• Rare Irish Breeds– www.kerrycattle.ie– www.irishspecklepark.com– www.dextercattle.co.uk

Rare Irish Breedswww.kerrycattle.iewww.irishspecklepark.comwww.dextercattle.co.uk

Breeding Game

• http://pbskids.org/dragonflytv/games/dog_breeding_v37.swf