MEIOTIC nondisjunction during spermatogenesis can give rise to abnormal numbers of Y chromosomes. When present with a single X chromosome, excess Y chromosomes may be associated with mental retardation.1,2 When a supernumerary Y chromosome is coupled with two or more X chromosomes, low intelligence and the clinical picture of Klinefelter's syndrome is observed.3 No constant abnormality has been ascribed specifically to an extra Y chromosome.
Sandberg et al4 explained the relative genetic inactivity of the supernumerary Y chromosome by postulating a low content of genes in the Y. Townes et al2 speculated that the Y chromosome might behave like the X chromosome, and undergo specific inactivation when more than one is present in the cell. Uchida et al5 have made the puzzling observation that individuals with an XXYY chromosome complement have highly characteristic dermatoglyphic patterns, while the XXY and XYY people do not.* This suggests
WATERMAN DF, LONDON J, VALDMANIS A, MANN JD. The XXYY Chromosome Constitution: Deoxyribonucleic Acid Replication and the Xg Blood Groups. Am J Dis Child. 1966;111(4):421–425. doi:10.1001/archpedi.1966.02090070119019
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