Breeding with a New Mutant
Author: Roy Robinson
From Issue 37 Apr 2001
Editor's note: Roy Robinson was known personally to several BHA members in the 1990s. His book Colour Inheritance in Small Livestock is regarded as something of a "bible" for small animal breeders and fanciers. He was a geneticist and author of many scientific papers in a variety of journals, especially the Journal of Heredity. He also wrote books on inheritance in larger animals such as cats and dogs. Aside from his scientific and literary output, there is little written about him or his life. If any readers can point toward sources of information about him, we'd love to include it here. Please use the contact page.
All of the varieties of hamster have arisen by mutation of the genes. The majority have produced novel colours (e.g. Cream, Grey, etc.) while others have produced novel coats (e.g. long hair, rex). How should one proceed if a new mutation is discovered?
In the first instance, It has to be established if the new form is actually a new mutation. For example, suppose one has been breeding Black Eyed Creams for a number of generations. All of the offspring have been Black Eyed Creams. However, in the fifth generation. a red eyed cream baby Is produced. Could this represent a new mutation? Well a mutant producing red eyes Is known already as Cinnamon. Before one could claim a new mutant the red eyed cream would have to be mated to a Cinnamon.
If the resulting babies are Cinnamon, the answer is no. The new mutant is actually the Cinnamon gene which has remained hidden in the black eyed animals until a chance mating between two carriers brought the gene to the surface. This "hiding" is not unknown for a recessive gene despite the passage of five generations of Black Eyed Cream breeding. On the other hand, suppose a unique colour has been found? The natural tendency is to mate the form to other colours to see "what will happen". This may satisfy one's curiosity but it is not the right way to proceed, genetically speaking. The first task is to establish if the new colour is inherited and, if so, how.
The correct procedure will be to mate the new colour to an unrelated normal coloured or Golden hamster. If all of the offspring are Golden (say 10 or more), this will indicate that the new colour is not inherited as a dominant (otherwise, babies of the new colour would have been produced). Two possibilities exist: (1) that the new colour is not inherited: or (2) that the colour is inherited as recessive to Golden.
It is too soon to accept that the new colour is not inherited, so one should proceed as if the colour is inherited as a recessive. To do this, the Golden offspring are mated to each other. It is rather difficult to obtain pure breeding Goldens and not all of the first generation offspring need be Golden. In this case, provided all of these are known colours, these should be discarded to concentrate on the Goldens.
The majority of the second generation offspring will be Golden but, if the new colour is inherited, about a quarter will be of the new colour. Now suppose after breeding a number of litters, the new colour has failed to appear. Does this mean that the new colour is not inherited? The answer lies in the number of second generation offspring which are bred. The colour may not have reappeared due to chance.
Fortunately, for a quick breeding animal such as the hamster, this is not too difficult. If the new colour has not reappeared after breeding the above numbers, the likelihood Is that it is not inherited.
However, it is possible that the chance of reappearance of the colour is less than one quarter. Suppose animals of the new colour are less likely to survive in comparison to Golden? This is not unusual, new mutants often have less stamina than normal. If this is regarded as likely, the number of second generation offspring must be increased, say, to 50 or more.
The possibility must be considered but one can make an educated guess whether it is likely by examination of the original individual. Does it appear healthy and lively or is it undersized or less energetic than normal? If the answer is no, the likelihood of it being a random non-genetic event will have to be accepted. These events do occur but rarely. The chances are that a new colour (or coat type or whatever) will be inherited.
Suppose, now, that the first mating to the unrelated Golden produced progeny, some of which are of the same colour as the mutant. Two explanations are possible: (1) that the Golden just happened to be a carrier of the new colour: or (2) the new colour is inherited as dominant. As the Golden is unrelated, the first possibility will be discounted for the moment.
To prove the dominance of the colour, the mutant coloured offspring should be mated to each other. The expectation is that one quarter of the young will be Golden. But suppose only young of the new colour are produced? In that case, at least 16 or 24 offspring, as discussed above, should be bred to minimise the risk of Golden babies not being bred by chance.
However, suppose all of the 16 or 24 babies are of the new colour? One must assume the Golden must have been a carrier however unlikely this may have seemed. The procedure will be to assume that the colour is inherited as a recessive and to proceed to the second generation as described above.
The purpose of this note is to argue that breeding with a potential new form should be placed on a sound basis. In this manner, the mode of inheritance of the colour can be quickly established. That is not all, it is just as important to discover precisely how the mutant gene produces the new colour. To establish the gene's mode of action as geneticists say. If the new gene has been combined with previously known genes. this may still be possible but could be rendered more difficult. These could confuse the issue and possibly lead to incorrect conclusions.
Finally, it would be wise to seek advice if you are unsure how to proceed. Indeed, it is probably wise to seek advice in any event. Seeking advice will not distract from the fame or excitement of finding a new mutant gene.