~ ~ ~ MERLE  GENETICS ~ ~ ~
aka:  Dapple
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I will do my best to 'try' to educate those wishing to learn the truth about the merle gene.  
Others have consistently posted knowingly false or unproven or even dis-proven theories on the merle gene in their bias attempt to make others fear the gene.

KNOWLEDGE  IS  A  WORTHY  OPPONENT
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"THE  TRUTH  ABOUT  MERLES"

Merle is a modifying gene found in many breeds of dogs including the Rat Terrier and Harlequin Pinscher.

It works to lighten areas of the dogs body in which the gene touches, sometimes

including the Eyes and Nose.

M- a merle allele responsible for merle colouring of the coat - dominant gene
m - an allele responsible for normal coat pigmentation - recessive
mm- Normal pigmentation - NO MERLE - homozygote of mm - genotype.
Mm - single merle - heterozygote
​MM -  homozygote merle

An indepth research has shown even more forms of Merle genetics
and can be found by searching for Mary Langevin - Merle Genetics.

(Langevin et al: 2018)

Additional Merle Genetics include Mh,  Ma+, Ma, Mc+, Mc bringing the

total to 7 when you include M and m.

Wall eyes (*blue eyes caused by Merle gene) are not inferior in vision

to normal colored eyes.

In single form the Merle gene only modifies areas of the dogs coat and

sometimes the eye color.

A  homozygous merle (*once called double merle), is exactly that - the

breeding of a merle to a merle resulting in merle offspring with 2 Merle genes.  
There is no special gene these dogs carry, they simply have two copies

of the normal merle gene.  

The homozygous merle gene is considered semi-lethal as it does
not adversely affect every dog with the homozygous merle gene inheritance.

 In homozygous form (*double merle) the gene can cause in utero death of fetus

or deaf, blind, deformed offspring.  

Keep in mind this is NOT the single merle form.  

The answer to not producing homozygous merles is to simply not
breed Merle to Merle.  

It's a pretty simple concept even for those on a learning curve.  BUT I regress ...

When breeding merle to merle there is a doubling up of the Merle gene and 25% of the HOMOZYGOUS  MERLE offspring  resulting in excessive white coat.  

(100 puppies X 25% = 25  25 x 25% = 6  so on average 6 out of a 100 puppies
from Merle to Merle breeding have the possibility of having genetic

issues from breeding Merle to Merle).    

It is that 'WHITE" which causes deafness and while the doubling up of the merle gene can cause the deafness so can any associated white gene such as the Piebald gene.  

LSU states "Evidence suggest that deafness is inherited in a
non-Mendelian manner in piebald breeds".  LSU went on to state in their article

that all 18 Merle Chihuahuas and the  4 Merle Dachshunds  in their testing

panel were all single merles and none had a deaf ear.  

LSU further stated "Consequently, the deafness in this study cannot be positively

attributed to the SILV mutation ... The SILV gene has been eliminated as a

cause of deafness in the Dalmation breed".

Deafness is completely determined by the pigment of the hair in the inner ear.  

If the hair lacks pigment then the dog will be deaf -
irregardless if it is merle or not.  Many white dogs of other breeds

(*ie Boxer, Dalmation, White Bull Terrier, Piebald Dachshund)
have been known to be prone to deafness and yet they do not have the

merle gene associated with their deafness.

There has been so much 'bad research' related to the merle gene that we have

to wonder who is monitoring these professionals leading us astray.  

Gen Mark claimed to of found the gene related to merle, more specifically

calling it the "SILV" then in 2006 recalled the testing due to inaccurate results being found.   The Journal of Veterinary Medicine in 2009 posted an article stating that while

merle dogs had a slightly elevated deafness rate over dog breeds

homozygous for the piebald gene, the merle dogs also had a lower deafness

rate than that of the Dalmation or White Bull Terrier.  

Genomia claims to of identified the merle gene on CFA 10 or Canine Chromosome 10.   Genetic DNA studies performed at LSU, Texas A&M,
Cornell, Auburn, Clemson and the University of Viriginia have some

very different views of the Merle gene than some others.  Some of their studies

have shown that the merle gene may affect some breeds differently than others.  

Their studies showed dogs having both the Homozygous (*double) Merle and piebald gene have a greater propensity for producing deafness in their offspring.  

Double merle breedings in Catahoulas during their research did not show to have an
increased incident of deaf offspring.  

Testing for Merle gene is being offered by several Laboratories such as Orivet (* U.S., Australia and New Zealand), IDEXX in Canada, U.C. Davis, Embark, Paw Print, GenSol and others.  

LSU has a test called the BAER test available for those wishing to have their

dogs hearing tested.
LSU states on their website "Breeds with white pigmentation are most affected".
LSU also list 97 breeds of dogs with Reported Congenital Deafness and

VERY FEW of those breeds listed have the merle gene associated with it.

No 2 merles are ever just alike and their markings are as distinctive as finger-prints.

The merle gene has long been a bias subject for myth and false statements

with a sprinkling of truth woven into the story.

With all of this being said we can only hope some will be less likely to jump on the

Merle-Haters band wagon.

The Double Merle gene is semi-lethal in some Merle Lengths.

Some Merle X Merle breedings are highly UNETHICAL breedings.
Merles with certain Merle lengths can have severe health issues, be blind, deaf, deformed and/or die in-utero.

 HPA and BYA do not allow Merle x Merle breedings or Merle x Merle registrations.

There is a MERLE GENETIC TEST to test for Merle Length as shown above

and a chart to follow to breed merle dogs safely and responsibly.

ALL MERLE Breeders should be testing and breeding Merles Responsibly.

Please Check out the NEW Research and the Breeding Chart.

https://images.app.goo.gl/7agmN5o4TUYuqRCZ9

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m - non merle

Mc 200-230 - cryptic merle

Mc+ 231-246 - cryptic merle plus

Ma 247-254 - atypical merle

Ma+ 255-264 - atypical merle plus

M  265-268 - merle (*classic/standard)

Mh  269+ - harlequin merle

Please note the harlequin merle shown here and found in the

Mosaic Yorkies and Harlequin Pinschers is NOT the same

Harlequin gene found in Great Danes.

SAFE BREEDINGS:

no pigment deleted to white, no impairments

m/m

m/Mc

m/Mc+

m/Ma

m/Ma+

m/M

Mc/Mc

Mc/Mc+

Mc/Ma

Mc/Ma+

Mc/M

Mc+/Mc+

Mc+/Ma

Ma/Ma

LOW  RISK  BREEDINGS:

some impairment may occur, mainly auditory

m/Mh

Mc/Mh

Mc+/Ma+

Mc/M

MEDIUM  RISK  BREEDINGS:

can have vision and/or hearing impairments

Mc+/Mh

Ma/Ma+

Ma/M

Ma+/Ma+

HIGH  RISK  BREEDINGS:

vision and hearing impairments are common

Ma/Mh

Ma+/M

Ma+/Mh

M/M

M/Mh

Mh/Mh

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