This study investigates the presence and function of Y-chromosome-specific reiterated DNA (it-Y DNA) in individuals with aberrant Y chromosomes. The authors isolated and radiolabeled it-Y DNA, which represents at least 10% of the Y chromosome's DNA, and used it to perform reassociation assays with DNA from normal and variant individuals. The results show that it-Y DNA is primarily located on the long arm of the Y chromosome. However, the study found no evidence that it-Y DNA plays a role in male determination. The reassociation rates of it-Y DNA were significantly altered in individuals with specific chromosomal abnormalities, such as those with a doubled long arm or a deleted portion of the long arm. These findings suggest that while it-Y DNA is not involved in male determination, it may have other regulatory functions that are yet to be fully understood. The study also highlights the potential of using mutant-based approaches to purify specific sequences of it-Y DNA and map the chromosomal organization of various DNA classes.This study investigates the presence and function of Y-chromosome-specific reiterated DNA (it-Y DNA) in individuals with aberrant Y chromosomes. The authors isolated and radiolabeled it-Y DNA, which represents at least 10% of the Y chromosome's DNA, and used it to perform reassociation assays with DNA from normal and variant individuals. The results show that it-Y DNA is primarily located on the long arm of the Y chromosome. However, the study found no evidence that it-Y DNA plays a role in male determination. The reassociation rates of it-Y DNA were significantly altered in individuals with specific chromosomal abnormalities, such as those with a doubled long arm or a deleted portion of the long arm. These findings suggest that while it-Y DNA is not involved in male determination, it may have other regulatory functions that are yet to be fully understood. The study also highlights the potential of using mutant-based approaches to purify specific sequences of it-Y DNA and map the chromosomal organization of various DNA classes.