This article was first written by Eddie Crutchley in 1998 as part of a supplement to the NCS gazette.
INTRODUCTION
Plainly no gene is actually lethal in its action, however, the homozygous state of the Gunning Black and the Wilson White where the genes for either black or white are in double dose has not appeared as a live animal. We should actually modify this statement to say that no black or white animal has been produced which has lived to an age when it is possible to prove that it carries two genes for this dominant characteristic. The test would be to have such an animal mated to a large number of standard animals , if it was male, or to have a large number of offspring sired by a standard male if it was a female. If all the young showed the dominant characteristic then it could be assumed that the animal in question was a homozygous dominant. Similar to the condition where the homozygous Beige is mated to standards and all the young are heterozygous Tower Beige. So far no animal has been produced, in the black and white colour varieties mentioned above, which has produced in such a manner and this has led to the conclusion that the combination of two such dominant genes is a lethal mix. At what stage in the development this combination proves to be lethal is a matter of conjecture.
Does the effect take place at conception when the sperm meets the ovum?
Does the combination prevent the developing embryo from implanting in the wall of the womb?
The evidence taken from the book, "The Breeding of Mutation Chinchillas" by Mildred Adams where she asserts that when two homozygous white animals are mated together then the production of kits is reduced by 25 % (the homozygous offspring are not produced) seems to indicate that this is the case. I am rather sceptical about this and feel that this is really stretching the theory to its limits since in practice it is known that many more kits are conceived than are born. There are many reasons why the embryos may not attach to the womb wall and I do not discount the above as one of them but the number of animals produced will have more to do with the condition of the mother at conception than upon the genetic code which the embryo contains. One thing is certain, that nobody has yet claimed to have had a Gunning Black or Wilson White which only produces its own phenotypic colour in its offspring over a sufficient period of time and scale. Until such a time arrives we will call this combination of genes lethal.