What Does Normal By Descent (NBD) mean?
When a dog tests Normal it means he is carrying two normal copies of the gene in question, therefore he can only pass on a normal copy. When two normal tested dogs are bred their off-spring will also carry two normal copies, hence the term NBD. However there’s one important aspect being forgotten. This rule only holds true if you are using gene based testing. If you use marker tests or linkage tests you must test every generation. This is why AKC and OFA will only certify first generation NBD’s from gene based testing and WILL NOT certify NBD’s from marker and linkage testing.
The JRT Health Registry only accepts test results from the University or Research facility that isolated the gene for the disease. We then accept NBD’s when tested relatives provide the necessary proof of Normal linage for that offspring providing the test is also from the university that isolated the gene.
So please remember if your terrier has been tested at a facility using marker/linkage tests you must test all of your offspring, as these tests are probability tests and the genes are subject to rearrange in sequencing in the next generation, therefore the offspring cannot be considered NBD’s.