|
Genetics Can Be Fun
Part 1
Author:
DR. BRUCE M CATTANACH
Downs Edge, Harwell, Oxfordshire OX11 0JJ
Tel: (0)1235 835410
Fax: (0)1235 820584
www.steynmere.com
I have often thought with envy about dog breeding at the turn of the Century. This must have been a truly exciting period. It was a time of construction when older breeds and varieties were melded together to make new and exciting ones, each developed for specific purposes. Today, crossbreeding is no longer a recognised option but for the first 50 or so years of this century, crossbreeding to allow the introduction of new or otherwise desirable characters into established breeds was permitted by the Kennel Club, and this too must have been fascinating. I believe that only three backcrosses were needed before registration was again permissable. Nowadays, however, with K.C. registered dogs, pure breeding is the only option. Crossbreeding for any purpose is not considered, and I'm sure that even the idea may be thought of as heresy by most present-day breeders.
During my 50 or so years in Boxers I have, like everyone else, pretty well accepted the status quo. The challenge has been to produce the top class specimen excelling in type, construction and temperament etc.. But, in Boxers, the need to dock tails has, for me, always been an irritant. Why does one have to cut something off to achieve the required overall appearance.
Why, therefore, not develop a Boxer with a naturally short tail - and maybe with erect ears too, if one prefers this image, instead of the cropped ear still largely accepted on the Continent or in American? How easy would it be in any case to introduce a gene from one breed into another?
With such thoughts in mind several years ago, I looked up the literature on short tails and ear carriage to see what might be possible but, finding the evidence sparse and unconvincing, I went no further. However, on coming across a couple of related Boxers with short, screw tails soon afterwards, I was prompted to see if the condition was inherited. I bought the two dogs, one a male from the South West and the other a female from Yorkshire, placed them in pet homes and when they were old enough, mated them together. A healthy litter of seven pups was obtained, but all had full length, normal tails. It therefore seemed unlikely that the condition was inherited; and I was already aware that abnormalities of tail development are fairly common in dogs as I know they are in laboratory mice. This could have been the end of the story, but the tail docking issue that has been emerging in recent years has gradually converted my flights of fancy about inherited short tails in Boxers into perceived need. And similar thinking by two astute Pembroke Welsh Corgi breeders, Peggy Gamble (Blands) and the late Patsy Hewan (Stormerbanks) led me to look seriously upon what I began to see as a realistic option.
They had asked me to look into the inheritance of a bob-tail condition that exists in a few show lines, notably Patsy Hewan's Stormerbanks. Apparently the condition had been a characteristic of the breed in its early days as a working farm dog. The pedigree data I was given suggested a simple dominant inheritance, with about half the progeny from bob-tail x normal outcross matings showing the effect. Tail length, I was told, varied from almost tailless to about one-third normal and no associated abnormalities had been seen. There were no data from bob-tail x bob-tail matings, which was worrying, because from genetic studies upon similar tail anomalies in mice it might be expected that animals with two doses of the responsible gene might not survive to birth. On the other hand, were the condition one of those described in the scanty dog genetic literature, there was a possibility that the double dose animal might survive, so that the condition might breed true. This, at least, might fit better with the existence of the gene in working farm dogs. Interestingly, some 50 - 60% of Swedish Vallhunds are born with bob-tails and may carry the same gene. So far as I have been able to discover, there are no associated abnormalities in this breed either, but there appear to be no records which would indicate if the condition might ever breed true. A few other breeds also appear to carry either this bob-tail gene, or perhaps another with similar affect, and different modes of inheritance have been suggested.
It is now a matter of history that Peggy Gamble (jointly with Cliff Whitwell) bought a Stormerbank bitch with a bob-tail, crossed it with a dog of her breeding to establish a bob-tail line. A bob-tail dog, Vaquera of Pemwell, from this first mating was to become the sire of Peggy's first bob-tail champion (made up at Bath 1994, I think). Therefore, could the gene be crossed into the Boxer? Peggy Gamble was willing to help and, for me, the opportunity was too good to miss. It would really be fun to try and breed a Boxer with an inherited short tail. The attempt would also permit evaluation of the difficulties of transferring a single gene from one breed to another, a procedure which might have wider applications someday in the world of dog breeding. And, of more immediate scientific genetic interest, DNA analyses could contribute to the Canine Genome Mapping Project under way both in this country and in the United States. Plans were made for a Boxer x Pembroke Welsh Corgi cross.
THE CROSS
The first attempt was not successful. I opted to try a last litter from our Steynmere Top Bid, who had been a reasonably successful show bitch in her day. It meant a trip up to Yorkshire one Christmas eve. My wife was not impressed. Biddy, however, thought it all the greatest fun, but despite a good mating, achieved with the help of a series of drawers stacked high to compensate for the height difference and much handling dexterity by Peggy Gamble, no litter resulted. It seemed that I would have to start from scratch with a younger bitch. But I did not want to commit a show bitch to such a cross. The solution was to keep a white one, such as commonly occur in Boxer litters, specifically for the purpose. White Boxers are not usually kept as they do not conform to the Standard of the breed, and they are also at risk of being deaf.
A white bitch was to appear in a 1991 litter by Ch Skelder Singing Sleuth ex our Charivari Amber of Steynmere, a Ch Garnet Gelert of Steynmere daughter.
Steynmere Pearl (known as Polly, short for Polyfilla) was not deaf and, apart from her white colour, became a very nice bitch. So, in November 1992, off I trailed to Yorkshire to visit Peggy Gamble and her bob-tail Corgis. Prof Morton, a specialist in artificial insemination at the University of Birmingham was on standby in case of emergency. However, again with Peggy Gamble's expertise, a natural mating to Cliff Whitwell's Vaquera of Pemwell was achieved. In due course we got our litter.
THE GENETIC EXPECTATIONS
A first prediction from crossing of two breeds (Fig. 1) is that, barring the segregation of individual genes in each breed, eg red versus brindle, all the progeny should look alike. But, what else could be expected?
Corgis have a fawn colour with the same genetic basis as Boxers, but they differ with regard to several known genes;
1. the white markings are caused by a different form of the gene responsible for whites and white markings in Boxers;
2. the legs are short (dominant);
3. the coat is long relative to that of the Boxer (supposedly dominant);
4. the ears are erect (supposedly recessive);
5. Corgis do not have the black masking factor (dominant); and finally,
6. the Corgi used in the cross had a single dose of the bob-tail gene (dominant).
The Corgi-Boxer crossbreds were therefore expected not only to be uniform in appearance; they should be fawn, have intermediate near-50:50 levels of white markings (piebald), perhaps show a black mask (dependent upon white markings), have short legs, a longish coat, and drop ears, but the bob-tail gene was expected to segregate such that only half the puppies would have bob-tails. Beyond this, the unique head features of the Boxer might be expected to give way to the more normal Corgi head.
THE LITTER
In total, 7 pups were born and all indeed looked alike. They weighed about 14ozs, and all were fawn. Confirming the genetic basis of Boxer and Corgi white markings, they all showed the piebald level of white markings (Fig. 2). Traces of black masks could be seen on some. But, more importantly, 5 had bob-tails of lengths varying from that of the docked Boxer (Fig.3) to about one-third normal, while the other 2 had tails of normal length. No other anomalies were detected at birth or subsequently. All the expectations were therefore met and the dominant bob-tail inheritance was further established. However, in our eyes the pups looked horrendously ugly, at least at birth. They simply looked like very bad, overmarked Boxers. Initially we did not like them at all.
By the age of 5-6 weeks things were better. The pups no longer looked like awful Boxers, but rather like an unrelated and somewhat cute breed (Fig. 4). And they all still looked alike. The Corgi overwhelmed. The heads were Corgi-like, the legs were short, the coats were longish and somewhat wavy, the tails of bob-tail pups (and normals) were free from kinks, though tended to bend over the back, but all the pups appeared to have drop ears. Only in eyes, expression and temperament did they resemble Boxers. They looked ideal puppies for little girls, and a photo in the vets' surgery a few weeks later had them selling like hot cakes. The "Borgies", as they were to be known, became famous in the local community and also at my Genetics lab where they were a source of much interest.
We had a Borgy party in our garden when the pups reached 7 months of age. Seen together they all then looked like strong Corgis, but one had erect ears (Fig. 5) which does not accord with the supposedly recessive inheritance of this character. On close inspection of the others, all the ears were found to be stiff, almost cardboard-like to touch, unlike the soft, velvety Boxer ear, and tended to stick out at odd angles. Erect ear carriage would therefore appear to be at least semi-dominant. It seems likely that if the ear is small enough it may stay erect, even with only one dose of the gene.
Two of the bob-tail pups were bitches and these were sold on condition that each would have a litter. Both had 6 month seasons and at 18 months we attempted to mate one of them, named Dolly (Fig. 6),to our Boxer male, Steynmere Foreign Service (Fig. 7).
Disaster. While it was love at first sight, the deed seemed impossible. She stood on her tip toes and he stood on his hocks, but to no avail. And attempts to use a platform were foiled by Dolly's refusal to be held by the collar. As a last ditch approach I rushed the pair off for an artificial insemination attempt by the UK expert, Garry England, at Potter's Bar. We were running late in the season by this time, but all went very well. However, no litter resulted. The other bitch, Tess, had come into season only two weeks after Dolly, but we had opted not to mate her. So, another 6 months went by. Then Dolly came into season again .
This time I was determined to get a natural mating and persuaded friend and neighbour, Gordon Seeney of Maranseen Boxers, to shed his principles regarding the whole business and come to help. Dolly was so ready mate, but still refused to be held even loosely by the collar. Sharp dewclaws slashed the back of my hand (a case for their removal if ever there was one), but with heavy duty lifting by Gordon we succeeded in getting a brief mating, if without a tie. The chances of her getting pregnant seemed remote, so when sister Tess came into season on cue two weeks later we opted to take her directly for artificial insemination. And this was done. But, both bitches became pregnant. Dolly had 9 pups and Tess 7, both completing their whelping in about 2 hours, and without any assistance. Moreover, both bitches reared their litters without loss or any intervention until weaning time. Borgy breeding was a doddle. I had 16 pups from which to choose one or more for the next generation.
In Part 2 of this article, the revelations of the backcross will be described..
Legends to Figures (Part 1)
Fig. 1 The introduction; the white Boxer and the Pembroke Welsh Corgi.
Fig. 2 The crossbred litter - all alike with near 50:50 (piebald) levels of white markings.
Fig. 3 Bob-tail and normal tail.
Fig. 4 The results - Polly and her crossbred litter.
Fig. 5 One of the crossbred puppies (seen here as an adult) had erect ears.
Fig. 6 Dolly, one of the two crossbreds used for breeding.
Fig. 7 Steynmere Foreign Service, the mate for Dolly and Tess.
Part 1 of this article described the cross of a Boxer with Pembroke Welsh Corgi having an inherited bob-tail. A primary object was to determine if through a series of backcrosses the Corgi bob-tail gene could be introduced into the Boxer. Here, the results of backcrossing two Corgi x Boxer crossbred bitches to a Boxer are described.
THE FIRST BACKCROSS: EXPECTATIONS AND ODDS
As both the crossbred dams and Boxer sire were fawn, all the pups were expected to be likewise, and all should have dominant black mask of the Boxer. However, all the main Corgi-Boxer differences (leg length, coat length, ear carriage) as well as tail type should separate out among the offspring. Moreover, because the Boxer sire, Foreign Service, carries the gene for white and the crossbreds carry both the Boxer and Corgi forms of the gene, further complexity regarding white markings was anticipated. It is perhaps best to present the expected outcomes in terms of the odds of their occurrence:
1. To take the project into the next generation, and also for practical and economic reasons, it was necessary to keep a bitch. Therefore, from the 16 puppies obtained in the backcross, only 8 on average might be expected to be bitches.
2. Any bitch to be of use for further breeding must, of course, have a bob-tail. Therefore, with a dominant inheritance, it could be expected that only half the pups would inherit the gene from their crossbred dams. Thus, of the possible 8 bitches, perhaps only 4 could be expected to have bob-tails.
3. Because of all the difficulties in mating short and long legged dogs, I desperately wanted any bob-tail bitch which I was lucky enough to get to have long legs. Again, only half of the possible 4 of interest might have this characteristic; maybe 2 out the original 16!
4. Then there was the coat length; only half again. Therefore, if I wanted to the short coat too, there would be only 1 chance in 16 of getting the combination wanted, a bitch with bob-tail, long legs and short coat. And this is without the white markings problem. Adding this:
1. one-quarter of the pups were expected to be white, with the risk of deafness that this would entail;
2. one-quarter were expected to show the piebald level of white marking like the crossbred dams;
3. one-quarter were expected to have flashy white markings like the sire; and,
4. one-quarter were expected to be near-solid, but carry the gene for the Corgi type of white markings.
THE RESULTS
At birth, the pups appeared to range from Boxer type to Borgy (Fig.8) and we could, of course, immediately recognise tail length; 7 had bob-tails (almost all of docked Boxer length and straight) and 9 had normal length tails. None had any unwanted abnormalities. And importantly, 4 of the bob-tails were bitches. So we were off to a good start.
In all, the base colour was fawn with black mask. The white markings were of the four expected types. Two pups were white, 4 were of the piebald type, 8 were flashy and 2 were near-solid. However, what stunned us most was that some of the pups looked like pure bred Boxers of pick of litter quality (Fig.9).
I was desperate to have one like this with a bob-tail but, frustratingly, these had long tails.
By about 4 weeks we could distinguish different leg lengths. There were 8 of each type and this could be better seen at yet greater ages. It was clear that the pups either had Boxer length legs or short legs. But leg length, tail length and colour were inherited independently to give all possible combinations. At 6 weeks the two litters contained puppies that seemed like a collection of different breeds (see examples in Figs 10-13).
Yet luck was with us for we did manage to get the critical combination of characters we wanted, even in this first backcross generation. Thus, of the 4 bob-tail bitches, one had the long legs and a short coat, and although Boxer white (with only two tiny red spots), she was not deaf.
More than this, Jane, as she was to be called, looked very like a Boxer, both as a small pup and subsequently when she reached normal Boxer size (Fig. 14). And her temperament was delightful, being Boxer in most ways if perhaps more sweet and gentle. In effect, we had got our "Boxer" back in the first backcross generation.
But there were other points of interest. Ear carriage and mouths were checked at later ages. Of 11 pups examined at 10 months, 4 had the stiff "cardboard" ears that could partially or completely stand erect (Fig. 15). This did not include our selected long legged, bob-tail, white bitch, but the 4 stiff eared ones were bitches, giving me thoughts on creating an erect eared Boxer. Six of the 11 were also undershot (including Jane), even if they were narrow of jaw. But with the teeth large and regularly placed. Head types all still tended towards Corgi, but were generally deeper and stronger, with some stop and wrinkle. Size varied considerably, some being quite small while one male was huge weighing in at 80lbs (Fig. 16).
Coat type was rather confusing. At about 8 weeks there appeared to be two coat types which I assumed would develop either as long coated like the crossbred dams, or short coated like the Boxer sire. But at 10 months there appeared to be several coat lengths. One dog was very short coated, as are many Boxers, several others fell within what I would still consider the normal Boxer range, but the remainder were definitely on the long side with some wave, although not nearly as long or as wavy as that of the dams. Contrary to the indications in the literature, therefore, more than a single gene seems to be involved in coat length and type.
In all the excitement of the Borgy breeding, the scientific component of the study was not forgotten. Blood samples have been collected from the original Boxer and Corgi parents, from all the first cross progeny, from our Boxer male (Foreign Service) used in the backcross and from nearly all of the 16 backcross generation pups. When I get blood samples from the remainder, Dr Jeff Sampson from Leicester will make DNA from them for analysis. Half of this DNA will be used in Cambridge as part of the UK Canine Genome Mapping Project and half will be sent to California where a similar programme with different genetic markers is in progress. The same collection procedure will be followed in subsequent generations as appropriate.
WHAT NEXT?
The surprising discovery at this stage was that few genes seem to distinguish two such diverse breeds as the Boxer and Corgi. Apart from those concerned with head properties, these specifically include those for leg and coat length.
The presence of finer points that distinguish the Boxer from other breeds could still be said to be variably evident however.
Thus, so far as even the most Boxer-like dogs from the first backcross were concerned, there still seemed to be something foreign about them. In the case of Jane, further development of head was required, she needed a larger eye, stronger and harder musculation, a shorter, harder coat and more bone. So, further improvements were needed, but perhaps little more than those involved in the ordinary task of trying to breed good show animals.
Fortuitously, because of the dominant inheritance of the main unwanted characteristics (short legs and long coat), there was no need to worry about these appearing in Jane's descendants. She had the long legs and a short coat and therefore did not carry the short leg and long coat genes, and so could not transmit them. All that needed to be done was to breed selectively over a further generation or two of backcrossing the bob-tail gene into the Boxer to create a bob-tailed but otherwise typical "Boxer". And, this might be achieved in a single further generation, with a judicious choice of sire and a little bit of luck.
THE SECOND BACKCROSS: OBJECTIVES AND EXPECTATIONS
In this generation there were just two objectives in addition to retaining the bob-tail gene; the improvement in breed type plus show points, and re-establishing the accepted colour.
For our selected bob-tail bitch, Jane, we needed a stud dog excelling in breed type, size and substance and with good head and eye qualities. And, as usual in choosing a stud dog, he had to be of good show quality. Finding such a dog would not be easy, and then there was the issue of colour.
Trivial as this is, it was a critical point. The possibility of getting a white puppy with all the other characteristics wanted, but then found to be deaf, was a horrendous thought. Therefore, priority was given to ensuring that all the pups would be coloured. If colour had been the only consideration, this could easily have been resolved through the use of any "solid" stud dog, that is, one which does not carry the gene for white (identified by white markings on the limbs confined to the toes). Such a dog when mated with a white would produce only flashily marked pups, carrying only a single dose of the responsible gene.
The problem in practice was that, as almost all show dogs are flashily marked and therefore carry the gene for white, finding a solid dog of show quality, and with the specific characteristics needed would be difficult. In addition, would a committed breeder of show stock allow any significant stud dog to be used on a crossbred bitch?
Fortunately, there are people in Boxers who are as wrapped up in the breeding of animals as I am. Enquiry quickly raised two breeders who had potentially suitable dogs and were willing to participate in the project. The MacLarens from Scotland had a suitable dog but he was still too young at the time Jane came into season. However, the Rallings who had a dog with absolutely all the requirements. The dog, Boxella's Chief of Zenmaxkay, is a Continental import of outstanding German - Dutch parentage.
Not surprisingly for this breeding he is big substantial male, excelling in bone substance and above all breed type. More than this he has produced progeny which excel in head qualities and which have notably good eye shape and size. And, as well as qualifying as a solid on the basis of his limited white markings, it was clear from his past breeding performance that he did not produce whites; he did not carry the gene. A brindle, he was known to carry the gene for red/fawn.
In summary, the expectations for the litter were as follows:
1. all the pups should be coloured and have flashy white markings within the recognised Boxer range. There would be no whites, solids or piebalds;
2. half the litter should be brindle like the sire and half should be red/fawn, Chief being a carrier of red and Jane being a red/fawn "under" the white, as indicated by her two tiny spots of red/fawn coat;
3. half the litter should inherit the bob-tail gene from Jane and be bob-tails, while the rest would have normal length tails;
4. all the pups should look like Boxers, with no "throwbacks" to the dominant Corgi characteristics (short legs, long coat); and,
5. head types, hopefully, would be much improved and, barring any total surprises, these should fall within the range exhibited by the parents.
Stud arrangements were made, and when Jane came into season when about 18 months old, she was duly mated to Chief. Being of normal Boxer height there was no difficulty in mating her.
Part 3 of this article, will describe the outcome of the mating and consider future options.
Legends to Figures (Part 2)
Fig. 8 Crossbred Dolly and backcross litter; a range of types
Fig. 9 Backcross pups (1/4 Corgi) of Boxer pick of litter quality.
Fig. 10 Boxer markings, short legs, longish coat, long tail.
Fig. 11 Piebald white markings, short legs, short coat, bob-tail.
Fig. 12 Boxer markings, long legs, short coat, long tail.
Fig. 13 Boxer conformation, piebald white markings, long legs, long coat, bob-tail.
Fig. 14 Jane, the first bob-tail 'Boxer' at 12 months. Boxer white, long legs, short coat, bob-tail. Compare her with her mother, Dolly, Part 1, Fig. 6.
Fig. 15 Erect to semi-erect ears in a first backcross bitch at 10 months.
Fig. 16 An 80lb dog at 10 months.
Fig. 17 Boxella's Chief at Zenmaxkay, the 'solid' dog mated to Jane.
|
