In a Certain Community,a Mutant Allele for Tay-Sachs Disease Is

Essay

In a certain community,a mutant allele for Tay-Sachs disease is prevalent.This mutation removes a Hind III restriction site in the gene sequence.A probe is available for this region,with the following homology:

Two couples in this community are expecting children.Each couple has a DNA test to determine if their child will have Tay-Sachs.The results of the Southern blot,probed for the region described above is shown below.
$$\begin{array} {cccccc } \text { M1 } & \text { F1 } & \text { Child 1 } & \text { M2 } & \text { F2 } & \text { Child 2 } \\\end{array}\\\begin{array} { | l l l l l l | } \hline \underline{\quad\quad} &\underline{\quad\quad} & \underline{\quad\quad} & \underline{\quad\quad}& \underline{\quad\quad} & \underline{\quad\quad}\\\underline{\quad\quad}&\underline{\quad\quad} & & \underline{\quad\quad} & \underline{\quad\quad} & \underline{\quad\quad} \\ \hline\end{array}$$

Using these results,how would you counsel the couples?