Part of the repeated deoxyribonucleic acid (DNA) in the chicken genome had a clustered organization. The following description of clustered repeated sequences is derived both from analysis of DNA segments cloned in lambda and from hybridization of individual cloned sequences to Southern blots of restricted total DNA. A cluster usually exceeds 20 kbp in length and consists principally, if not entirely, or repetitive DNA. Each cluster contains one cope of several different repeated sequences. The individual sequences occur several hundred times in the genome, but only once per cluster. Many of the clusters contain the same assortment of sequences but in scrambled order. In the genome, those repeated sequences that are elements of clusters occur mainly within the clustered context and are seldom, if ever, found as isolated elements flanked by nonrepeated DNA. These aspects of cluster organization suggest that the clustered sequences undergo limited rearrangement, maintaining the associations within clusters but allowing variability of sequence arrangement from cluster to cluster. The clusters that occupy the cloned DNA segments together represent at least 10% of the repetitive DNA of the chicken.

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