If this disease is genetic--what are the possible genotypes of the parents? If the disease is a chromosomal abnormality, describe the abnormality.

This disease is genetic, so the possible genotypes of the parents are Tt and Tt.  This is the only way a child can get this genetic disease.  It is also possible that this child could be a carrier.  These outcomes are shown in the punnett square below.  If the outcome is tt that means that the child has Tay Sachs disease, Tt means that the child is a carrier of this disease, and TT means that the child does not have this disease and cannot pass it on to his or her children.
              

	T	t
T	TT	Tt
t	Tt	tt

 punnett square created by me

http://nervous-system.emedtv.com/tay-sachs-disease/inheriting-tay-sachs.html