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03 Heritability


This article is from the Juvenile Renal Disease, by Susan L. Fleisher

03 Heritability

George Padgett, D.V.M., a geneticist and professor of pathology at
Michigan State University, told me that JRD affects about 20 breeds.
In most of the breeds in which it has been studied it is a simple (one
gene), autosomal (not sex linked), recessive (both parents have to
carry the gene) disease. Both parents of an affected puppy are
therefore defined carriers. The presence of just one affected puppy
determines that both parents are carriers. Littermates of an affected
puppy have a 66% chance of being carriers. Aunts and uncles of an
affected puppy have a 50% chance of being carriers, as do
grandparents. According to Dr. Padgett, if a sire has produced an
affected puppy, and is therefore a defined carrier, he has also proven
bitches who are probably clear: those who when bred to him have
produced sizeable litters in which there were no affected puppies.
"Proven" is used rather loosely here, since statistically a dog mated
to a carrier and producing six normal offspring would still have a
17.8% chance of being a carrier. Twelve normal offspring would reduce
that chance to 3.17%. The preceding figures which refer to simple
autosomal recessive anomalies are from Malcolm B. Willis' book
Genetics of The Dog. If the disease is caused by a simple autosomal
recessive gene, both parents must be carriers of the gene to produce
an affected puppy. However, even if only the sire or only the dam is a
carrier, the other parent being clear, 50% of all the puppies born are
carriers themselves. If the cause of JRD is polygenic, several genes
would be necessary collectively in order for the disease to occur. In
Samoyeds the mode of inheritance is now known to be x-linked
recessive. In that breed, only males are affected with the disease,
but females pass it on through the x chromosome.


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