Identification of a case of Y:18 translocation using a Y-specific repetitive DNA probe

We have used a recombinant DNA clone derived from the Y-specific 3.4-kb repeats for in situ chromosome hybridization and Southern blotting analysis to identify a case of de novo Y;18 translocation. The proband has a chromosome complement of 46,XY and a variant chromosome 18 with a Q-bright and C-positive short arm. The father has a normal male karyotype of 46,XY. The mother has a female karyotype of 46,XX and an unusually large Q-bright satellite on one chromosome 22. In situ hybridization with the 3.4-kb probe to the metaphase preparations of family members indicated that the additional Q-bright material in the proband's variant chromosome 18 derived from the Y chromosome of his father, and not from the variant chromosome 22 of his mother. On Southern hybridization, the proband had approximately twice the amount of 3.4-kb repeats per cell as his father. These observations suggest a de novo genetic rearrangement in the proband which probably occurred during the father's spermatogenesis.