Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother's X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother's to make a boy (XY).

A Newcastle University study suggests that an as-yet undiscovered gene controls whether a man's sperm contains more X or more Y chromosomes, which affects the sex of his children. On a larger scale, the number of men with more X sperm compared to the number of men with more Y sperm affects the sex ratio of children born each year.

The immune system's battle against invading bacteria reaches its peak activity at night and is lowest during the day, according to Stanford researchers who based it on experiments with Drosophila melanogaster and reveal that the specific immune response known as phagocytosis oscillates with the body's circadian rhythm. They presented their findings at the American Society for Cell Biology (ASCB) 48th Annual Meeting, Dec. 13-17, 2008 in San Francisco. "These results suggest that immunity is stronger at night, consistent with the hypothesis that circadian proteins upregulate restorative functions such as specific immune responses during sleep, when animals are not engaged in metabolically costly activities," explains Mimi Shirasu-Hiza of Stanford University.

Is obesity all in your head? A new study says that genes that predispose people to obesity act in the brain and that perhaps some people are simply hardwired to overeat. An international research team found six new genes that help explain body mass index and obesity, and all but one of the genes are tied to the brain rather than to metabolic functions, such as fat storage and sugar metabolism. In addition to the six new genes, the study also confirmed the role of two other genes previously associated with obesity, said co-principal investigator Goncalo Abecasis, an associate professor at the University of Michigan School of Public Health. The study is in the journal Nature Genetics.

The first demonstration that a single adult stem cell can self-renew in a mammal was reported at the American Society for Cell Biology (ASCB) 48th Annual Meeting, Dec. 13-17, 2008 in San Francisco.   The transplanted adult stem cell and its differentiated descendants restored lost function to mice with hind limb muscle tissue damage.

Meiosis, the process of halving a germ cell’s chromosomes in preparation for egg or sperm production, has been one of the most studied areas of cell biology. But in mammals, the field has been divided over the question of whether meiosis is triggered by a signal within a cell or by a signal coming from the cell’s environment. Now new research from the lab of Whitehead Director David Page reveals that both sets of signals are needed to initiate meiosis.

Determining the mechanisms that shape biological membranes has long been a tricky business. Like a factory assembly line, eukaryotic cells are organized into membrane-bound, functional compartments called organelles. For instance, the nucleus is the repository of genetic information and houses the machinery that creates the messenger RNA transcripts, which direct the synthesis of new protein. Secreted proteins are synthesized in a second organelle, the endoplasmic reticulum (ER), which are exported to the cell surface by a third organelle, the Golgi complex. All membrane bound organelles are characterized by dynamic changes in membrane structure that are closely coupled to the function of these compartments.