In-Service: Animal Breeding and
Genetics
Dr. Alan Fahey
March 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
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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
DiscreteVariation
Continuous Variation
2
1
0
Red
Roan
White
Quantitative traits have
continuous variation
Qualitative traits have discrete
variation
Quantitative traits are controlled
by many genes
Qualitative traits are controlled by a
single gene
Each gene has a small effect
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)
Ss, ss (non-starchy)
SS (starchy)
Kk, kk (wrinkled)
KK (smooth)
Cross:
KKSS x KkSs
Alleles:
K K S Sx K k S s
F1 Genotype:
KKSS;KKSs;KkSS ;KkSs
F1 Phenotype:
All smooth and starchy
The expression of the heterozygote is identical to the
expression of the homozygous dominant genotype
Partial Dominance
Yellow
YY
Green
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
No Dominance
Shorthorn Cattle
White
Roan
Red
rr
Rr
RR
Cross:
Rr x Rr (Roan x Roan)
Alleles:
R r x
F1 Genotype:
RR; Rr ;Rr ; rr
F1 Phenotype:
red; roan;roan; white
R
r
The expression of the heterozygote is exactly midway to
the expression of the homozygous genotypes
Over Dominance
Yy
Yellow
Green
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
Inbreeding and Crossbreeding
Inbreeding v Crossbreeding
2007 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
Inbreeding
• Related animals have more genes in common
• Animals of outstanding genetic merit are
likely to have relatives that have above
average genetic merit
C
C
www.eurogeneaiservices.com
Inbreeding
• 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. fatherdaughter 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 % in Irish Cattle
Charolais (-∆-), Limousin (--), Hereford (-•-), Angus (--), Simmental
(-▲-), and Holstein-Friesian (-₀-) breeds across year of birth.
Mc Parland et al., 2007
Inbreeding Depression
Inbreeding
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)
Performance
Hybrid Vigour= extra performance
above mid-parent mean
Breed A
AxB
Breed B
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 Testing
2007 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 resources
General 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
Breeding Game
• http://pbskids.org/dragonflytv/games/dog_br
eeding_v37.swf