What are the possible genotypes of the parent?

Parents that have children affected by XP:

Heterozygous (Xx) and Heterozygous (Xx)

Heterozygous (Xx) and Homozygous Recessive (xx)

Homozygous Recessive (xx) and Homozygous Recessive (xx)

There are no chromosomal breaks, gaps, or rearrangements. There is increased frequency of UV-induced chromosome breaks and sister chromatid exchanges.