If this mode of inheritance is confirmed as the only mode operating, the matter of concern then, in this respect, is reducing the frequency of both long-tailed offspring and Spina Bifida.
There are then three possible gene combinations:
If the animal has a "T" allele present, i.e., its genetic make up is TT or Tt, then it would be expected to have a stumpy tail. If the genes were tt the animal would have a long tail. However, occassionally, for some unknown reason, the "T" does not have its usual dominant effect and the animal will have a long tail, even though it does have a "T" allele. This effect would produce more long-tails than would be expected.
The defect may be seen as a faulty formation of the underside of the spine with varying degrees of defective development of the internal organs.
Spina Bifida is a congenital (present at birth) defect of development,marked by a defective closure of the bony encasement of the spinal chord, through which the meninges (membranes covering the brain and spinal chord) may or may not protrude as a sac. If they do protrude, the condition is known as Spina Bifida Cystica; if not, it is Spina Bifida Occulta. This defect can range all the way from a form with few visible symptoms to a complete open spine.
The causes of Spina Bifida are not fully understood. they are thought to be a combination of genetic and environmental influences.
Spina Bifida commonly affects the lower back regions of the spine. The sac, if there is one, may collapse while still in the uterus, but fills with cerebrospinal fluid soon after birth. If the sac is not covered with skin it can rupture and perhaps lead to meningitis.
Spina Bifida can be accompanied by varying degrees of paralysis, depending on involvement of the spinal chord and/or its nerve roots. Since the paralysis is usually present in the foetus, it can lead to peoblems such as club foot or dislocated hip. In addition, the paralysis may affect the sphinciters (closure muscles) of the bladder and rectum, resulting in genetiourinary disorders and damaged kidneys. An abnormal, convex shape to the curve of the spine may occur and can hinder surgical closure. Hydrocephalus (accumulation of cerebrospinal fluid within the skull) also accompanies many cases of Spina Bifida.