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. Housekeeping 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. Scientists discovered in 2002 that the X chromosome is unusual because it contains very few of the most important genes needed for basic cell function - dubbed "housekeeping" genes. Now the team, a collaboration between researchers at the University of Bath and Uppsala University, along with members of the FANTOM consortium , have found out why. They analysed the world's largest compendium of data on gene activity (expression) and looked at how activity on the X chromosome compares with that on other chromosomes.