A new study has confirmed that males and females have at least 1 thing in common - both sexes up-regulate X-chromosome gene expression.
The finding by a group of scientists including UNC biologist Jason Lieb, PhD, supports a longstanding hypothesis that explains how males can survive with only one copy of the X chromosome.
"The issue is important because many diseases are tied to a defect in a regulatory mechanism within the cell," said Lieb, who is also a member of UNC Lineberger Comprehensive Cancer Centre.
Women have two X chromosomes, while men have one X and one Y.
The lack of a 'back up' copy of the X chromosome in males contributes to many disorders that have long been observed to occur more often in males, such as hemophilia, Duchene muscular dystrophy, and certain types of colour blindness.
Biologists have been debating how organisms and cells manage the imbalance between X and other chromosomes for years, with the dominant theory being that both sexes up-regulate the expression of X-linked genes, essentially doubling their expression to '2X' in males and '4X' in females.
Then, to correct the imbalance that now appears in females, they then 'turn off' one of the hyperactive X chromosomes, resulting in a balanced '2X' expression of those genes across both sexes.
Lieb and his colleagues re-analysed data used in previous analyses, along with new data from humans, mice, roundworms, and fruit flies and found more evidence that the up-regulation hypothesis is correct - but with some interesting twists across species.
In mammals - humans and mice - both males and females up-regulate X-chromosome gene expression and females then equalize expression by turning off the one X chromosome.
The study has been just published in the journal Nature Genetics.