Abstract
Under normal conditions, men have 46 chromosomes, including 44 numbered chromosomes (two copies of each chromosome numbered 1 to 22) and two sex chromosomes, one X and one Y. Men with Klinefelter syndrome have an arrangement with an extra sex chromosome: 47,XXY instead of the usual 46,XY (Bock, Understanding Klinefelter syndrome: a guide for XXY males and their families, su NIH Pub. No. 93–3202, Office of Research Reporting, NICHD, agosto 1993).
Chromosome abnormalities can occur for the first time when a sperm or an egg is formed; fertilisation of this mutated gamete leads to conception of affected offspring (homogeneous Klinefelter syndrome).
In some cases, genetic mutations can occur for the first time after sperm fertilises egg, when the embryo is formed and cells are dividing. Post-zygotic division error may occur only in one or more than one cell line. These are conditions of mosaicism for the extra X chromosome.
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Dipresa, S., Garolla, A. (2020). Causes of Extra Chromosome(s). In: Garolla, A., Corona, G. (eds) Klinefelter’s Syndrome. Trends in Andrology and Sexual Medicine. Springer, Cham. https://doi.org/10.1007/978-3-030-51410-5_3
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DOI: https://doi.org/10.1007/978-3-030-51410-5_3
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