Organization and heterogeneity of sequences within a repeating unit of human Y chromosome deoxyribonucleic acid

Abstract

Fragments of 3.4 kilobases (kb) are released from DNA of human males, but not DNA of human females, by cleavage with restriction endonucleases HaeIII, EcoRI or EcoRII. Most, if not all, reiterated DNA which is specific for the Y chromosome (it-Y DNA) is present within these male-specific 3.4-kb molecules. Although such 3.4-kb molecules are themselves localized to the Y chromosome, this is not true for all sequences within them. At least 2 distinguishable types of reiterated sequences are found within each 3.4-kb molecule. One type consists of at least 2 families which are highly reiterated and are not confined to the Y chromosome. The other type is composed of an estimated minimum of 39 families, each moderately reiterated and localized to the Y chromosome. Y-specific and non-Y-specific sequences are interspersed with one another in the same 3.4-kb molecule. In the average 3.4-kb molecule, 3 800 nucleotide lengths of Y-specific sequences alternate with 4 250 nucleotide lengths of non-Y-specific sequences. Since the total number of families of Y-specific sequences, calculated on the basis of reiteration frequency and total abundance in a male genome, greatly exceeds the number of Y-specific sequences present in a single 3.4-kb molecule, it follows that the population of these 3.4-kb molecules is heterogeneous.