The Bourns Test Litters for Dayblindness in Malamutes
Around 1960, Dr. Kenneth Bourns, then an assistant professor of Zoology at the University of Western Ontario, and a breeder of Alaskan Malamutes, had 3 puppies in a litter of 10 that seemed to have problems seeing during the day, but not at night. Dr. Bourns went to Dr. L.H. Lord of the Ontario Veterinary College at Guelph for assistance. They started on a series of test matings that expanded to include a second kennel and Dr. Lionel Rubin, well-known for his work on inherited eye diseases. The disorder, given the name hemeralopia, is now also known as inherited cone dysplasia.
The story actually begins in the mid-50s, with the mating of a male to four different females. In the published account, the dogs are not identified either by name or even by number, which makes the story somewhat difficult to follow. To simplify things, I will call this male Alpha. As his mates are not critical to the remaining account, they can remain nameless. However, four of their progeny (one from each dam) will be designated M1, M2 (male), F1 and F2 (female).
[The litters between two dayblind dogs are designated "A", those between a dayblind and a carrier "B", and those between two carriers "C".]
When M1 was mated to half-sister F1, a litter (C1) of 10 was obtained which included 3 dayblind pups. This would be Bourns' litter, described above. Subsequently, two unaffected sibs from the C1 litter were bred to each other producing a litter (C2) of 9, with 3 dayblind. A third unaffected bitch from the litter was bred back to her father (M1) and produced a litter (C3) of 6, of which 2 were dayblind. The three litters, together, produced 25 pups, 8 of which were affected. As this is about as close as you can get to the perfect Mendelian 1/4 for a recessive trait, that mode of inheritance was strongly suggested.
The second group appears to be from the other kennel, though the paper does not clearly indicate which litters are from which kennel. F2 was mated to an unrelated male. One of the females (F3) from this litter was subsequently mated to her grandfather (Alpha) and produced at least one dayblind pup (F4). I believe it likely that F4 was acquired by Bourns and his colleagues for the test breedings. [Animals from both kennels were used for the test litters, but are not identified. However, one may make an educated guess as to which these were.]
F4 was bred twice to her grandmother's half-brother (M2) to give 16 pups, 5 of which were dayblind (litters B1a and B1b). Two of the dayblind bitches were then crossed to a dayblind male from the C2 litter, and he was also crossed to one of his dayblind sisters. Each mating was repeated to give a total of 6 litters where both parents were dayblind. If the trait is recessive, then the parents would have to be homozygous, and only homozygous pups would be expected. If the trait is fully penetrant, all should be dayblind. All 25 pups from these six litters were dayblind.
The same dayblind male was also mated with a phenotypically normal bitch from the B1a litter to produce litters B2a and B2b - total 13 pups, 6 affected (indicating that she was a carrier).
One additional litter included in the data is between a dayblind male from the C1 litter and a phenotypically normal cousin. This litter produced 4 live and 1 stillborn pup. All four were dayblind! However, when the 5 "B" litters are added together, there are 15 dayblind and 17 normal progeny, which is in good agreement with the expected 50:50 ratio. Thus, though some of the litters show surprising deviations from the expected ratios, the numbers are too small from any one litter to draw firm conclusions. [Ideally, one would like at least 30 in each group before attempting any statistical testing.]
Group A (affected x affected: expect all affected)
Group B (affected x carrier: expect 50% affected)
Group C (carrier x carrier: expect 25% affected)
Because all these dogs are inbred on Alpha, the simplest conclusion would be that Alpha was a carrier. However, the possibility cannot be ruled out that the bitches to which he was mated were all carriers and that he was clear. Be that as it may, though I would be very surprised if any of the dogs from the test litters produced descendants, there is no indication that Alpha did not have other descendants or relatives who continued to pass on the defective gene.
Summary based on "Hemeralopia in Dogs: Heredity of Hemeralopia in Alaskan Malamutes" by Lionel Rubin, T.K.R. Bourns and L.H. Lord, American Journal of Veterinary Research, Mar. 1967, pp. 355-357.
Prepared by Dr. John B. Armstrong, University of Ottawa. May 1997.
NetPets® Main Page
The Dog Center