IF IT weren’t for “junk” DNA, women would be in trouble. Some of this
apparently useless DNA may be essential for silencing one of their X
chromosomes, say researchers in Ohio.
In mammals, one X chromosome is enough for both sexes, so females would get a
lethal double dose if one X weren’t shut down (New Scientist, 1 April,
p 4). This is done by wrapping up one X very tightly, with the help of RNA made
by a gene called Xist. Two years ago, Mary Lyon of the MRC’s Mammalian
Genetics Unit in Oxfordshire suggested that junk DNA…
