What could be the possible result of founder effect on genetic variation

Fa child has tay sach's disease, what would her parents' genotypes be? a) her father is heterozygous; her mother is heterozygous. b) her father is heterozygous; her mother is homozygous dominant. c) her father is homozygous dominant; her mother is homozygous dominant. d) her father is homozygous dominant; her mother is homozygous recessive.