Scientists believe the fatherhood gene which is inherited from both a man's parents, comes in one of three variations and affects the number of sperm carrying male or female chromosomes.

The British scientists say because of the gene, men inherit a tendency to have more sons or daughters from their parents and a man with many brothers is more likely to have sons, while a man with many sisters is more likely to have daughters.

The scientists from Newcastle University say men with a version of the gene known as "mm" produce more sperm with the Y chromosome and are likely to have sons, while another variant, known as "mf", produces roughly equal numbers of sperm with the female X and male Y chromosomes which gives a man a 50/50 chance of having a son or daughter - the third variant, "ff", produces more X sperm and more daughters.

The study involved research into 927 family trees containing information on 556,387 people from North America and Europe dating back as far as 1600 - but despite the suggestion of the existence of three types of fatherhood gene, the gene itself remains elusive.

According to researcher Dr. Corry Gellatly, from the University of Newcastle, the system possibly balances out gender numbers and the gene that is passed on from both parents, which causes some men to have more sons and some to have more daughters, may explain why the number of men and women are roughly balanced in the population.

Gellatly says if for example there are too many males in the population, females will more easily find a mate, so men who have more daughters who will pass on more of their genes, causing more females to be born in later generations.

In the work now published in Cell, the Bockamp/Eshkind work group reported on the construction of a type of gene switch with which a specific characteristic - in this case fluorescence - can be switched on or off in a living mouse. "We can therefore externally control gene expression in stem cells," Bockamp added. "In the field of switchable, genetically-modified mouse models, we are among the leaders in Germany and want to use this extremely effective technology increasingly in future."

Control over the labeling process is indispensable - after all, the aim is to observe the behavior of the stem cells. Should the cells divide because they have been activated - perhaps by an injury - the fluorescence in the two daughter cells is reduced to 50 percent, then to 25 percent if they divide again, and so on. "In this way we can accurately determine how often the labeled stem cell has divided once the labeling process has been stopped," said Bockamp. His colleagues in Lausanne and Heidelberg found out that there is a small group of special blood stem cells that divide extremely rarely, i.e. only once every 145 days or five times during the life span of a mouse, and which can switch between dormancy and self-renewal in an emergency. Bockamp pointed out that the actual analysis of the cell division processes is not possible in Mainz, due to a lack of technical infrastructure. The group plans to focus increasingly on cancer research in its future work.

Original publication:

Anne Wilson, Elisa Laurenti, Gabriela Oser, Richard C. van der Wath, William Blanco-Bose, Maike Jaworski, Sandra Offner, Cyrille F. Dunant, Leonid Eshkind, Ernesto Bockamp, Pietro Li , H. Robson MacDonald and Andreas TrumppHematopoietic Stem Cells Reversibly Switch from Dormancy to Self-Renewal during Homeostasis and RepairCell, 4 December 2008, doi:10.1016/j.cell.2008.10.048

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