A cloned chicken DNA fragment includes two repeated DNA sequences with remarkably different genomic organizations.

The presence of both single copy sequences and repeated DNA sequences with a broad range of repetition frequency is a hallmark of the eukaryotic genome. The advent of recombinant DNA technology has made it possible to isolate cloned DNA fragments that encompass two or more DNA sequences with different repetition frequencies. This provides the first opportunity to investigate the structural relationships in the genome of DNA of the different repetition frequency classes in a thorough and systematic way. A cloned fragment of the chicken genome containing two different repeated DNA sequences has been used for this purpose. By hybridization of radioactive restriction fragments of the cloned DNA to filter-bound restriction fragments of total chicken DNA, it has been determined that the 5.5-kilobase inserted DNA in this clone contains a copy of each of two long, repeated DNA sequence elements with different repetition frequencies. These two repeated DNA sequences have very diverse arrangements in the chicken genome. The results establish that, in addition to the interspersion of single copy and repeated DNA sequences in the chicken genome, repeated DNA sequences with very different structural characteristics can be interspersed with one another. Thus, the chicken genome is a complex network of related sequences in which some members of a family of repeated DNA sequences are associated with other, nonhomologous repeated DNA sequences, while other members of the same family are flanked by single copy DNA.