We hear more and more these days about genetic defects, and with good reason. In addition to hip dysplasia, we now worry about osteochondritis, elbow and patella dysplasia, half a dozen distinct eye problems, and more. At first it was thought that x-rays, screening and selection would ensure genetic health for our dogs. But 30 years of hip x-rays have not wiped out HD, although progress has been made in some breeds. Screening and selection for one defect is fine.
Veterinary costs soar.
You must select against so many traits that your breeding program is turned upside down, especially if you fancy a serious working breed, as I do. In a small kennel on limited funds, breeding only two litters a year, it just isn't practical. The books on dog breeding hold no answers. They tell us how to use inbreeding, linebreeding and outcrossing, and they teach us the basics of Mendelian genetics, but these help to manage one or two traits at a time. Genes are linked in groups on chromosomes.