The Merle Gene

Extract from "Coat Colour in the Cardigan Corgi". An interim study of colour inheritance.

By Ken Linacre.

The blue merle Cardigan Corgi is essentially a modified tricolour. The dominant gene M produces dilution of dark coat colour in a blotched or patched pattern. If combined with tan point pattern, with either clear or brindle points, a blue merle is produced. If combined with other dark colour coats, so called off-colour merles result. If present in a red or sable, the merle is often observd in the grey puppy coat when the pup is in the nest, but may be totally masked in the adult red dog.

The M gene frequently produces whole or partial silver or white marking in the iris of the eye, and such eye markings are known in colours other than merle when the M gene is present.

Merle inheritance is illustrated in Table 5.

In 5a) i) the normal practice of mating tan points with blue merle is illustrated; tan point and bue merle offspring are produced. Note that the tan point offspring do not carry the M gene; they cannot transmit it and can freely be used for interbreeding with stock of other colours.

5a) ii) shows the cross with a brindle tan point, which produces blue merle with brindle points.

5b) shows the result of mating blue merle to blue merle. The resulting litter may be expected to contain both tan point and blue merle puppies. In addition, som puppies carrying two M genes may be expected. The presence of two M genes may have profound effects. Such animals may have largely white coats with only limited patches of colour, and cases are recorded where eyes are small or even absent and ears are affected. It is claimed that the MM foetus is sometimes reabsorbed.

It is possible to obtain blue merle offspring from stock of non-merle breeding, if it carries the a^t tan point gene.

5 c) shows the result of mating a red/sable carrying a^t with a blue merle. The litter would be expected to contain tan point and bue merle pups. It would also contain red offspring which did not carry the M gene and offspring which did: the latter might or might not show evidence of this in the coat colour or pattern.

In 5d) a similar pattern resulting from mating a brindle with a blue merle is shown. Here brindle puppies which do not carry M are probable, together with puppies which do carry M: these may be off colour merles or may not indicate merle in the coat colour.

5d) uses the brindle formulation a^ya^tEe^br; the results of using the other brindle formulations a^ya^yEe^br, a^ya^ye^bre^br and a^ya^te^bre^br may be similarly derived. Note that mating of a blue merle with a black brindle is quite different from using a tan point "black".

As in the mating of two blue merles, the mating of other animals which each carry the M gene can produce MM puppies: these may have the consequent defects, and instances of this are recorded.

Animals which are not merles but carry the a^t and M gene, can when mated with tan point stock or in matings which can produce tan point stock, produce bue merle offspring.

In 5e) such a mating is shown. It may be recalled that the blue merle colour was "recovered" after being "lost" in Cardigan Corgis for many years, from such mating. Three important cases are recorded.

a) Samswn Bach, the blue merle dog from which the Rozavel blue merles descend, was by Minor of Taxicar, a red dog with a white marked eye, out of Jill Fach, a tricolour bitch (CWCA 1962 Year Book).

b) A puppy which died, by N.Z.Ch. Binder of Greenfarm, a brindle dog, out of N.Z.Ch. Kentwood Fflur, a tricolour bitch. This mating also produced red, brindle and tricolour offspring (CWCA 1960 Year Book).

c) Farsdale Silver Smoke, a blue merle dog bred by Mrs Farley in California by Ch. Aru Dan, a red ad white dog out of Brown One, a brindle and white bitch. (Data provided by Mrs Glennis Miller).

In these cases it is interesting to note that Binder of Greenfarm was said to have been "a lovely dark brindle with quite a lot of blue about him" and Brown One was said to have had a "silver sheen" overlying the brindle. Although the colour of all the ancestors of these dogs are not known, there are no obvious blue dogs for several generations.

Table 5 – Inheritance ivolving the "merle" gene

a) tan-point to blue merle

i) a^ta^tEEmm (tan point clear) x a^ta^tEEMm (blue merle clear points)

Ž a^ta^tEEmm (tan-point clear)

Ž a^ta^tEEMm (blue merle clear points)

ii) a^ta^tEe^brmm (tan-point brindle) x a^ta^tEEMm (blue merle clear points)

Ž a^ta^tEEmm (tan-point clear)

Ž a^ta^tEEMm (blue merle clear points)

Ž a^ta^tEe^brmm (tan-point brindle)

Ž a^ta^tEe^brMm (blue merle brindle points)

b) blue merle to blue merle

a^ta^tEEMm (blue merle) x a^ta^tEEMm (blue merle)

Ž a^ta^tEEMM (double merle)

Ž a^ta^tEEMm (blue merle)

Ž a^ta^tEEmm (tan-point clear)

c) red/sable to blue merle

a^ya^tEEmm (red sable) x a^ta^tEEMm (blue merle)

Ž a^ya^tEEmm (red/sable)

Ž a^ya^tEEMm (red/sable and carrying merle – possible off-colour merle)

Ž a^ta^tEEmm (tan-point clear)

Ž a^ta^tEEMm (blue merle)

d) brindle to blue merle (using one of the brindle formulations)

a^ya^tEe^brmm (brindle) x a^ta^tEEMm (blue merle)

Ž a^ya^tEEmm (red/sable)

Ž a^ya^tEEMm (red/sable and carrying merle – possible off-colour merle)

Ž a^ya^tEe^brmm (brindle)

Ž a^ya^tEe^brMm (brindle and carrying merle – possible off-colour merle)

Ž a^ta^tEe^brmm (tan-point brindle)

Ž a^ta^tEe^brMm (blue merle brindle points)

Ž a^ta^tEEmm (tan-point clear)

Ž a^ta^tEEMm (blue merle clear points)

e) brindle carrying merle with-tan point clear

a^ya^tEe^brMm (brindle carrying merle) x a^ta^tEEmm (tan-point clear)

Ž a^ya^tEEmm (red/sable)

Ž a^ya^tEEMm (red/sable and carrying merle – possible off-colour merle)

Ž a^ya^tEe^brmm (tan point brindle)

Ž a^ya^tEe^brMm (blue merle brindle points)

Ž a^ta^tEEmm (tan point clear)

Ž a^ta^tEEMm (blue merle clear points)

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