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XYY: Stereotype of the karyotype

It is not only people with disorders of sex development/intersex conditions who experience gender-related stereotyping by society

XX female fetuses can acquire an extra X chromosome, leading to XXX females (triple X syndrome, also known as trisomy X), and XY male fetuses can acquire an extra Y chromosome, leading to XYY syndrome (which affects as many as one in 600 males). Chromosome abnormalities can be picked up in a karyotype test, where the size, shape and number of a person’s chromosomes are examined under a microscope.

Triple X females are usually fertile, but sometimes go through the menopause early. XYY men tend to be taller and more wiry than other men, and can suffer from severe acne. They are also reported have higher average blood testosterone than XY men.

XYY syndrome karyotype 47,XXY

The XYY syndrome karyotype of a male has an extra Y chromosome.


Wessex Reg. Genetics Centre/Wellcome Images

XYY men in particular have been negatively stereotyped by society. When the syndrome was first discovered, popular science writers speculated that the extra Y would make males more aggressive – and more prone to criminality – than their XY peers. (This view persists: the film ‘Aliens 3’ was set in a colony for XYY prisoners.)

The myth was backed up by some rather misleading statistics. A paper published in the ‘Lancet’ in 1968 claimed that the prevalence of XYY among male prisoners was 25–60 times as high as the prevalence in the general population. This prompted some to suggest that screening for XYY would identify potentially violent and criminal males. But the quality of this research was soon questioned (it was later pointed out that only two XYY male prisoners were identified in the study) and the consensus today is that there is no strong link between XYY and criminality, especially when social and economic factors are taken into account.

XYY men may tend to share certain features, but these are well within the ‘normal’ range of human variation. Indeed, more recent studies have shown that testosterone is usually well within typical ranges in teenagers and young men with XYY.

Lead image:

Carole Raddato/Flickr CC BY


About this resource

This resource was first published in ‘Sex and Gender’ in January 2006 and reviewed and updated in October 2014.

Cell biology, Genetics and genomics, Psychology
Sex and Gender
Education levels:
16–19, Continuing professional development