A study of chromosomal organization of repetitive DNA sequences by in situ hybridization.

Chromosomal DNA restriction fragments from Triturus cristatus carnifex, were cloned in pBR322. Five clones containing repetitive DNA sequences were analysed in terms of size, repetition frequencies, GC contents and interspersion patterns. All the data suggest that the cloned sequences are typical for the major repetitive classes found in carnifex and represent members of individual repetitive families. All five cloned sequences hybridize in situ to nascent RNA transcripts on lampbrush loops present in the heteromorphic region of chromosome 1. One of the cloned sequences is interesting in that it shows individual variation. The least repeated sequences are transcribed at many more loci than the more highly repeated sequences and are better represented in the total ovarian RNA.