Comparative sequencing of a multicopy subtelomeric region containing olfactory receptor genes reveals multiple interactions between non-homologous chromosomes.

In this study, we assess the evolutionary relationships among different chromosomal copies of a subtelomeric block of sequence. This block contains homology to three olfactory receptor genes and is dispersed on at least 14 different chromosome ends in humans. It is single-copy in non-human primates. We analyzed single nucleotide polymorphisms in two 1 kb subregions and a polymorphic Alu insertion within 181 copies of this block from 12 chromosome ends and found evidence for recent interactions between the subtelomeric regions of non-homologous chromosomes. First, several sequence haplotypes are each present on multiple chromosomes, and several chromosomes each have multiple alleles with divergent haplotypes. Secondly, the observed variation clearly indicates that chromosomes 5q, 8p, 11p and/or 15q have each received the block from at least two different sources by non-homologous exchange. In addition, we observe at least one ectopic gene conversion event. Awareness of such exchange among sequences on non-homologous chromosomes is critical for accurate analysis of these complex and dynamic regions of the genome.