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Inside the X-(Chromosome) Files

Not to stir up a battle of the sexes, but the X chromosome (females have two of them, while males have one) is five times larger than the Y chromosome, and has 10 times the number of genes. That means it carries more traits — and diseases — than the Y chromosome. The Y chromosome is important in determining a person’s biological gender. But it has much less of a say in someone’s genetic makeup, since the X chromosome likely has more than 1,000 genes whereas the Y chromosome has fewer than 80. And some scientists believe that over subsequent generations, the Y chromosome may lose even more genes.

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 The X factor, and why the sexes are so different

Scientists have deciphered the chromosome that explains the difference between men and women and holds the secrets to at least 300 inherited diseases. Chromosome X could reveal the precise machinery behind mental retardation, autism, colour blindness, muscular dystrophy, a host of other diseases - and even the colour pattern of calico cats. Haemophilia - an inherited condition linked to a gene on the X chromosome - played a role in the Russian revolution of 1917. Other X-linked genes, involved in gout, obesity, blindness, deafness, anaemia, cleft palate, epilepsy, leukaemia and infertility, affect the lives of millions.

Articles of Interest

Scientists discover why X chromosome lacks 'housekeeping genes'

Men have one copy, women have two, but scientists have long puzzled over why the human X chromosome mostly contains genes that are active in a small number of tissues. Now, a team of researchers led by the University of Bath studying the evolution of this X chromosome has discovered why it contains such an unusual mixture of genes. In humans, males have XY chromosomes, females have XX but only one of these is active, meaning that both sexes only have one active copy of the X chromosome.

Sexing the X: How the X Became the “Female Chromosome”

Unexpected.” “Counterintuitive.” “Intellectually surprising.”1 These were among the exclamations of researchers upon the 2001 discovery that the human X chromosome carries a large collection of male sperm genes (Wang et al. 2001). Although both males and females possess an X chromosome, the X is frequently typed as the “female chromosome” and researchers assume it carries the genes for femaleness.

The X chromosome: The supermom that's inside of us all

Although the precise details of its chemical structure and performance are only just emerging, the X chromosome has long been known and was named X by geneticists not because of its shape, as is commonly presumed - the non-sex chromosomes also vaguely resemble an "X" at times during cell division - but because they were baffled by the way it held itself apart from the other chromosomal pairs. "They called it X for unknown," said Mark Ross of the X Chromosome Group at the Wellcome Trust Sanger Institute in Cambridge, England.

Why Do Women Have More Autoimmune Diseases? Study Points to X Chromosome

The molecules that silence a woman’s second X chromosome can confuse the immune system, a new study suggests.

Why is the X chromosome so odd? Traffic analogy helped us crack the mystery

You may not be aware of it, but one of your chromosomes – the X chromosome – is considerably different from the rest and has posed a puzzle for scientists for over a decade. Early in mammalian evolutionary history, what is now the X chromosome was just like any of our other chromosomes. But at some point it evolved to be different. Unlike all other chromosomes, one of the two X chromosomes in women is inactivated in nearly all cells. It also has an extremely low mutation rate and – most perplexingly – the genes that are found on it are active in relatively few of our tissues. Now a study we recently published in PLOS Biology, has begun to shed light on what’s going on – by using a traffic analogy.

X Marks The Genetic Mystery

The X chromosome is one of those things that we learn about early on in school, and yet it still contains mysteries–ones that potentially have a direct impact on our health. Men have one X chromosome and one Y, while women have two X’s. This imbalance has led to all sorts of remarkable things–most remarkable of which is the fact that women shut down one of their X chromosomes–but which chromosome (mom or dad’s) depends on the cell.