Figure 2.21 on p. 32 shows the inheritance of Huntington disease in a family from a small village…

Figure 2.21 on p. 32 shows the inheritance
of Huntington disease in a family from a small village near Lake Maracaibo in
Venezuela. The village was founded by a small number of immigrants, and
generations of their descendents have remained concentrated in this isolated
location. The allele for Huntington disease has remained unusually prevalent
there.

a. Why could you not conclude definitively
that the disease is the result of a dominant or a recessive allele solely by
looking at this pedigree?

b. Is there any information you could glean
from the family’s history that might imply the disease is due to a dominant
rather than a recessive allele?