Humans are born with 46 chromosomes in 23 pairs. Most women are 46XX and most men are 46XY. Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome 45X or 45Y sex monosomies and some with three or more sex chromosomes 47XXX, 47XYY or 47XXY, etc. In addition, some males are born 46XX due to the translocation of a tiny section of the sex determining region of the Y chromosome. Similarly some females are also born 46XY due to mutations in the Y chromosome.
Sweat mutation may have helped us colonise Asia
WHO | Gender and Genetics
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By Michael Marshall. How did our species become the dominant one on Earth? Pinpointing the genetic changes that made this possible is one of the great challenges of evolutionary biology. Now, a team has developed a method that could allow us to reconstruct a detailed, step-by-step genetic history of our species spanning tens of thousands of years.
Republish our articles for free, online or in print, under Creative Commons licence. Some babies are born with a genetic variant that leads to atypical sexual development. It can result in the child being neither a typical boy nor girl. Genetic differences between men and women lie in sex chromosomes.