HETEROMORPHISM FOR A HIGHLY REPEATED SEQUENCE IN THE NEW ZEALAND FROG LEIOPELMA HOCHSTETTERI.

A satellite DNA sequence, Lhl, was cloned from the New Zealand endemic frog Leiopelma hochstetteri. Large tandem arrays of Lh1 were localized by in situ hybridization to the long arm of a small telocentric autosome in some individuals, but these arrays were absent from other individuals. Lh1 is also present in varying amounts on some supernumerary chromosomes in some individuals. Heteromorphism for the presence of Lh1 exists in two populations that have been separated by a sea channel since the end of the Pleistocene, indicating that the heteromorphism either has arisen repeatedly or has persisted for at least 10,000 years. Individuals lacking Lh1 thus appear to be at no significant selective disadvantage. The variation in Lh1 copy number probably results from its interstitial chromosomal location, which exposes it to more frequent unequal crossovers than the pericentromeric or telocentric locations of most satellite DNA. Lh1 may be parasitic or simply inert junk, but in either case it may be deleted or dispersed throughout the rest of the genome through unequal crossing over.