The diаgrаm belоw illustrаtes the results оf electrоphoresis of DNA sequences obtained from a family of two adults and three children, and amplified using PCR. The bands represent short repeating sequences of variable length. Results for another female (X) are included for comparison. Beginning with the origin there are six lengths of DNA fragments that have separated on the gel. For each fragment the individual that has a band at that basepair length on their gel will be listed. The largest fragment, fragment one: father, child one. Fragment two: child three. Fragment three: mother, child one, child two, X. Fragment four: X. Fragment five: father, child two, child three. Fragment six: mother. Which of the following is the best explanation for the fragment pattern for individual X ?