I got a brain in left hand drive

A long one today, sparked off by an interesting chatroom discussion the other day, which made it clear to me how the same technical term can vary from one application to another. We were discussing the basic principles of animal breeding, and how, in cats the term ‘out-cross’ means crossing two pure breeds, whereas in dogs the same term means mating two unrelated animals of the same breed. That lead onto a discussion about breeding and genetics in general, but as it was late at night there simply wasn’t time to explain it properly.

There was a lot of confusion about ‘in-breeding’ and ‘line-breeding’, with some expressing the view that these are wrong. However, people who are experienced in the practical aspects of breeding animals as well as having qualifications as geneticists explain it thus:

In-breeding is where the mating involves close relatives, such as grand-father to grand-daughter, half-brother to half-sister. This system will quickly ‘fix’ good points in the resultant offspring, and will also expose any major faults carried in the family line. It cannot create problems which aren’t already there - it can only bring them to light, which, if you’re concerned in trying to eradicate hereditary problems and breeding only healthy stock is a definite benefit to the breed as a whole. It can be used with great success, but only if the parent animals are of better-than-average quality to start with, and the breeder is knowledgeable enough to recognise when to stop. It’s certainly not a system that should be used without careful thought and planning, and a wealth of knowledge about all the animals in the pedigree, not just as names, but as individuals. This is the form of ‘marriage’ which, if it involved humans, would be forbidden by the Church.

Line-breeding involves using animals with common ancestors in their pedigrees three or four generations back, and is used by the majority of dog breeders. It helps ‘fix’ characteristics at a slower rate than in-breeding, but there’s less chance of potentially serious problems coming to light. They’ll still be lurking in the woodwork, though. If applied to humans, this marriage would be perfectly legal.

Out-crossing uses animals from totally different families. Offspring produced by this system will vary tremendously, and although the occasional super example will be produced, the vast majority will be mediocre at best. A carefully chosen out-cross is used every few generations to bring a new quality into a family, and then two or three generations of line-breeding will try to fix the good points and eradicate the bad ones that will inevitably have been introduced at the same time.

Providing the parents and grandparents are healthy (research, research!) basically the system that is most likely to produce the healthiest offspring is line-breeding. Out-crossing is a complete gamble. Also gene mutation is completely random and shouldn’t be associated with any particular breeding system. Indeed, a mutation is as likely to be of benefit to the species as otherwise.

In the effort to breed healthy pets for people to enjoy sharing their lives with, it’s vital to only breed from animals who aren’t carrying serious conditions. Where possible you make the most of the screening tests (BAER, hip-scoring, elbow-scoring, ophthalmic tests etc) while DNA tests are slowly being developed. In-breeding is one of the tools that, in the absence of laboratory tests, can be used to bring to light hidden conditions. When you know they’re there you can start to do something about them. If you deliberately avoid discovering them then all you’re doing is disseminating them to spread more widely in the population. And not just the ‘pedigree’ population.

Of course, the ultimate gamble, both looks- and health-wise, is a mongrel. Everyone knows that various breeds usually have a tendency to suffer from hereditary conditions – just like people do. What a lot of people forget is that crossbreeds and mongrels frequently suffer from the same hereditary diseases. Just because the parents are of different breeds it doesn’t mean all the ‘bad’ genes are instantly removed. Each parent passes 50% of their genes to their offspring, whatever breed they’re mated to. If a Labrador with dodgy hips mates with a German Shepherd with dodgy hips then the resulting pups are just as likely to have dodgy hips as if both parents had been mated to their own breed. The people who tell you that mongrels are healthier simply aren’t telling the truth. So if you choose a crossbreed (the offspring of two different pure breeds) or mongrel (where more than three breeds are involved in the first generation of the ancestry) - and there’s no denying they can be delightful animals - you really need to know the breeds which have gone into making them. But as many mongrels are the result of irresponsible owners allowing their pets to roam as the mood takes them the pups could be carrying absolutely anything in their genes – undoubtedly something from all the breeds that have gone into their make-up – and could be a timebomb. There again, they could have got lucky. What’s certain is that their parents won’t have been screened for genetic conditions, which is something responsible breeders do.

Don’t forget, the ultimate aim of the game is to produce animals which are most likely to live long, happy, healthy lives – not just take a chance. Reputable breeders do this by trying to identify carriers of hereditary conditions and remove them from the gene pool, leaving only those who are clear of the various conditions.

If anyone’s bothered to read through to the end of this, and is remotely interested in the subject, this and this may be of interest. I suggest they also read the works on genetics, both practical and theoretical, by Dr Malcolm Willis BSc, PhD. He can explain it so much better than I can!