Dachshunds, DNA & DNA Testing - The Dachshund Breed · PDF fileDachshunds, DNA & DNA Testing...
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Dachshunds, DNA & DNA Testing Cathryn Mellersh, Animal Health Trust, November, 2009
Transcript of Dachshunds, DNA & DNA Testing - The Dachshund Breed · PDF fileDachshunds, DNA & DNA Testing...
Dachshunds, DNA & DNA TestingCathryn Mellersh, Animal Health Trust, November, 2009
Talk Layout
• DNA – what it is, what it does, and how mutations in DNA cause
inherited disease.
• How a mutation progresses through a pedigree.
• How a mutation is tracked down
• Cord1 DNA test
• Genotype-Phenotype discrepancies & possible causes
• EBVs
• DNA is a very long molecule & is found in virtually every cell of the body.
• The canine genome consists of approximately 2,500,000,000 nucleotides of DNA
• If each nucleotide was 1mm long the canine genome would stretch from Land’s
End to John O’Groats and back.
• ALL the DNA is copied every time a cell divides
• DNA is responsible for every aspect of you and your dog that is not controlled by
the environment.
DNA
Coding DNA
AAU GGGGG A UUU CCCmRNA
A T V WTProtein
AC T GA A A CCCCT TG G
AAT GGGGG A TTT CCCDNA
Transcription
Translation
DNA
• DNA is a code/blueprint for every physical characteristic of a dog that is not
determined by the environment.
• The code is determined by the order of nucleotides along the DNA.
• ALL 2,500,000,000 nucleotides are copied every time a cell divides.
• Mistakes that arise are called MUTATIONS.
• Most mutations that arise are repaired whereas a tiny minority persist.
• Most mutations have no effect, whereas some can be advantageous.
• Some mutations have a deleterious effect & cause inherited disease.
*
Chromosomes
+
Egg Sperm
Cell division &
differentiation
X
X
Y
Y
fertilisation
38 pairs of autosomes &
1 pair sex chromosomes
DNA is carried on chromosomes
Inheritance of Mutation Down a Pedigree
Parents G-Parents G G-Parents G G G-Parents
Cord1 Mutation
• 44 nucleotide insertion in RPGRIP1 gene
• The insertion lies in a coding part of the gene
• The insertion changes the reading frame of the gene
• The change in reading frame generates a premature STOP codon in an
early part of the gene.
• DNA test launched in 2005
• The DNA test assays whether the dog under investigation carries zero,
one or two copies of the RPGRIP1 mutation.
• It does not assay for any other mutation anywhere else in the DNA.
Numbers of dogs tested
0
100
200
300
400
500
600
2005 2006 2007 2008 2009
MLHDs Tested 2005 - 2009
200
220
240
260
280
300
320
340
360
380
400
2007 2008 2009
MSHDs Tested 2007 - 2009
MLHDs
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
2005 2006 2007 2008 2009
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
2005 2006 2007 2008 2009
Normal allele frequencyMutation frequency
CarriersClearsAffecteds
MSHDs
0.30
0.40
0.50
0.60
0.70
2007 2008 2009
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
40.0%
45.0%
50.0%
2007 2008 2009
CarriersClearsAffecteds
Normal allele frequencyMutation frequency
Variation
• Not all dogs that are homozygous for RPGRIP1 mutation
develop PRA at the same age.
• Some dogs that are homozygous for RPGRIP1 mutation don’t
develop clinical signs until middle – late age.
WHY?
Could there be other genes involved?
Further Research
• Established a collaboration with David Sargan at University of Cambridge
Vet School to investigate the causes for the observed variation.
• Keiko Miyadera, PhD student – investigating the variation at a
molecular level.
• Claudia Busse, Ophthalmology resident – investigating the
variation at a clinical level.
Multiple Mutations
x
Gene 1 Gene 2 Gene 3
x x
Healthy eyes
Late-onset PRA
Early-onset PRA
phenotype
genotype
106
0
non-genetic or
environmental
effects
feed intake
season of birth
exercise
diet
radiographic variation
Why do we need Estimated Breeding Values?
BUT - only the genes
are passed on to the
next generation.
Muttley
Snoopy
Dougal
Pluto
Phenotypic scale
106
0
EBVs are simply estimated genetic liabilities of individuals to disease…
Genotypic scale
Dougal
Muttley
Pluto
Snoopy
REML analysis
Uses pedigree
and hip score
data to calculate
the genetic
liabilities of
animals to the
disease
What are Estimated Breeding Values?
