In humans, the correlation between recombination frequency and length of DNA sequence is, on average, 1 million bp per 1% RF. During the process of mapping the Huntington disease gene (HD), it was found that HD was linked to a DNA marker called G8 with an RF of 5%. (The Fast Forward box Gene Mapping Has Led to Treatments for Cystic Fibrosis explains that a DNA marker is a region of a chromosome in which differences in DNA sequence can be followed as alleles.) Surprisingly, when the HD gene was finally identified, its physical distance from G8 was found to be about 500,000 base pairs, instead of the expected 5 million base pairs. How can this observation be explained