Gross Anatomy and Histology of Tongue by Dr. Rabia Inam Gandapore.pptx
Coat Colour Genetics in the Connemara Pony Population of New Zealand
1. Coat Colour Genetics
in the
Connemara Pony
Population
of New Zealand
Sheila Ramsay
29 June 2013
2. Reasons for this Study
• to look at whether there is a correlation between
the development of Grey horse melanoma
and birth coat colour.
• to determine the level of the chestnut allele in
the New Zealand Connemara pony population.
• to determine the level of the cream dilution allele
in the New Zealand Connemara pony population.
4. Basic Colour Genetics of
Equus caballus
the domestic horse/pony
• The genotype is the genetic code and controls
every function in the body.
• The phenotype is what we see.
• The genotype and the phenotype can be at
variance with each other.
7. The Extension locus ‘E’
• ee = chestnut (recessive)
• Determines black or red
• Black is dominant
• EE or Ee = black
8. Agouti locus ‘A’
• Modifies black by changing black pigment to red
on specific areas of the body.
• Produces bays and browns.
• Does not affect chestnut (red)
• A is dominant A/A or A/a = bay or brown
• a/a = recessive
9. Cream Dilution Cr
Modifies the base coat colour by reducing the level
of pigmentation produced by the melanocytes
Is dominant. If the mutation is present it HAS to be
expressed.
Works only on red pigment.
One copy of the gene results in Palomino or
Buckskin (dun) or Smokey Black. (single dilution)
Two copies of the gene results in Cremello,
Perlino or Smokey Cream (double dilution)
10. Grey Modification ‘G’
• Is a dominant gene – if present in the genotype it
has to seen (expressed) in the phenotype. G/G, G/g
• The grey gene has a further mutation which causes
melanoma .
• The grey mutation works on the cells in the neural
crest of the developing embryo – well before cell
differentiation (about day 12 after conception)
11. What does this all actually
mean?
That what you see may just NOT be what you have
actually got, and is this one reason why many
people colour test their ponies.
12. Black + Cream + Grey
E+
a/a CCr
G+
All three of these photographs are of the same pony
13. Black + Agouti = Bay or Brown +
Cream + Grey
E+
A+
CCr
G+
15. A grey pony can be any colour
‘under’ the grey.
Unless you bred the pony the only way to know
for certain what is the birth coat colour of a grey
is, is by colour testing.
A GG parent can ONLY produce grey progeny
Gg/Gg matings have a 1:4 chance of producing a
non grey foal.
This is why the progeny of grey to grey matings
can surprise.
17. Colour Testing is a multi-step
process
This work requires significant ‘bench time’ in the lab.
1. Preparation of the sample then DNA extraction using a
thermocycler
2. Preparation of digest with the primers specific for each test,
restriction enzymes and then PCR.
3. Where necessary, incubation maybe required
4. The product is then run on an electrophoresis gel
19. How were samples obtained?
Some of the samples were collected at the same time as the blood
samples for the Hoof Wall Separation Syndrome (HWSS) research
at UC Davis. However there was also help from another source.
20. So what was looked at and
what were the results?
1. Relationship (if any) between birth coat
colour and melanoma development.
2. Allele distribution within the New Zealand
Connemara pony population
3. How this compares to that found in Ireland.
21. The Study Population
Of the 45 ponies in the study, nine ponies were
imported from Australia since 2005. 13 ponies are
the progeny of parents imported from Australia
since 2005. One pony is the product of frozen
semen from the UK. The balance of 22 ponies is
derived from the original bloodlines which were
imported to New Zealand from Australia, the UK
and Ireland in the 1970's and 80's.
22. Of the estimated 88 mares considered to still be
alive, 34 were enrolled into the study; therefore
this study covers 38.6% of the present estimated
female Connemara pony population in this
country.
The number of stallions registered since 1970
stands at 20 of which nine have died, been gelded
or exported, leaving 11 stallions standing at stud
at present. Of these 11 stallions, eight were
enrolled in this study. Thus 72.7% of the present
breeding stallions in this country are represented.
23. B a y B u c k s k in C h e s t n u t P a lo m in o B la c k
0
5
1 0
1 5
B ir th C o a t G e n o ty p e o f 4 5 C o n n e m a r a P o n ie s in N e w Z e a la n d
G re y
N o n -G re y
B a s e C o a t G e n o ty p e
Number
24. 33/45 of the ponies were phenotypically grey; 73.3% of the
study population. Of the 26.6% of non grey ponies 58.3% were
bay, a third were bay dilutes (buckskin) with chestnut being the
balance (8%)
The Grey phenotype in the
New Zealand Connemara
Pony Population.
In Ireland the prevalent colour in adult ponies is grey, with 70% of
ponies exhibiting this phenotype. Followed by bay (15%), dun
(12%) [buckskin] with the remaining 3% comprised of brown,
black, roan or chestnut.
25. 77.7% of the population tested were
either 'ee' (24.4% chestnut) or
carrying 'e' as a recessive (53.3%).
E e e e N o e
0
5
1 0
1 5
2 0
D is tr ib u tio n o f th e C h e s tn u t ( 'e ') A lle le in a P o p u la tio n o f
C o n n e m a r a p o n ie s in N e w Z e a la n d
G r e y
N o n G r e y
A l l e l e s
Number
26. The grey phenotype and
melanoma
1. Researchers in Sweden proposed that aggressive
melanoma appeared to be associated with the true
black genotype – E+ aa - homozygous or
recessive for Agouti (carries no agouti allele).
2. Their study population was the Lipizzaner.
3. The chestnut allele is not present in the
Lipizzaner breed.
27. PROBLEM!!!!!
How do you determine which genes might
influence melanoma development if you do
not have them all??
Study another ‘grey breed’ which does have
a full complement of colour alleles.
28. The results found in this study supports
the work released by University of
Minnesota
January 2013.
1. The extension locus E is not the determining factor
in melanoma development.
2. Agouti does appear to have a definite influence.
3. Agouti changes black pigment to red. It may have
functions in addition to colour change.
4. Presence of Agouti appears to be beneficial in
reducing the aggressiveness of melanoma
development BUT
29. It Appears
1. Homozygosity for grey is of the greatest influence
in melanoma development.
2. Multiple crossing of homozygous parents has an
exponential effect on melanoma development.
3. ‘aa’ increases the risk of melanoma development.
30. B la c k (E E / E e a a )
C h e s t n u t (e e / a a )
C h e s t n u t (e e / A a )
C h e s t n u t (e e / A A )
B la c k (E + / A a )
B la c k (E + / A A )
0
2
4
6
8
1 0
1 2
A g o u ti s ta tu s , B a s e C o a t C o lo u r a n d R e p o r te d I n c id e n c e o f M e la n o m a
in a P o p u la tio n o f G r e y P h e n o ty p e C o n n e m a r a P o n ie s in N e w Z e a la n d
M e la n o m a + ve
M e la n o m a -ve
A g o u ti S ta tu s a n d B a s e C o a t C o lo u r
Number
31. Take Home Message
1. Homozygous greys have a higher incidence of
melanoma.
2. AA ponies can NEVER produce a true black foal.
4. Smokey blacks (when they do not go grey) look
brown (often a seal brown)
5. Buckskins can sometimes look bay.
3. EE ponies can NEVER produce a chestnut foal.
