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If one of these atypical sperm cells contributes to the genetic makeup of a child, the child will have an extra Y-chromosome in each of the body's cells. [23] In some cases, the extra Y-chromosome results from nondisjunction during mitosis in early embryonic development. This can produce 46,XY/47,XYY mosaics. [23]
XYYY syndrome, also known as 48,XYYY, is a chromosomal disorder in which a male has two extra copies of the Y chromosome. The syndrome is exceptionally rare, with only twelve recorded cases. The presentation of the syndrome is heterogeneous, but appears to be more severe than its counterpart XYY syndrome.
48,XXYY syndrome is a condition related to the X and Y chromosomes (the sex chromosomes). People normally have 46 chromosomes in each cell.Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics.
The cells of those born male contain an X chromosome and a Y chromosome that make a pair and give instructions on which genes should be expressed in the body, the researchers said.
The human Y chromosome is composed of about 62 million base pairs of DNA, making it similar in size to chromosome 19 and represents almost 2% of the total DNA in a male cell. [ 54 ] [ 55 ] The human Y chromosome carries 693 genes , 107 of which are protein-coding . [ 56 ]
While all human chromosomes contain repeats, more than 30 million letters of the Y chromosome — out of 62.5 million — are repetitive sequences, sometimes called satellite DNA or junk DNA.
Among the six species, the Y chromosome exhibited much more variability than the X chromosome. For example, the X chromosomes of humans and chimpanzees are about 98 percent identical in makeup.
In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively. Hormone levels in the male parent affect the sex ratio of sperm in humans. [25]