The first large-scale, high-resolution study of human genetic recombination has found remarkably high levels of individual variation in genetic recombination, the process by which parents pass on a mosaic-like mixture of their genes.  In an article appearing February 1, 2008, in Science Express about 25,000 recombination events were identified to have occurred in the transmission of the parental genomes to 364 offspring.  High-resolution maps created using multiple SNPs allowed them to provide the precise location of where these genetic exchanges occurred, and assess the differences in recombination rates between individuals.  Recombination occurs during meiosis, a special kind of cell division that takes place only in the testicles and ovaries. In the process of making sperm or egg cells, the parent-to-be takes the chromosomes inherited from each of his or her parents and reshuffles them, swapping parts of one chromosome for the matching segments of the other version of that same chromosome. The result is a reproductive cell with a mosaic, or patchwork, of genes, about half from each parent, but shuffled together into entirely new combinations. This process leads to offspring having different combinations of genes than their parents and is thought to have many advantages. Errors in this recombination process during the production of sperm or egg cells underlie a variety of chromosomal abnormalities and can cause deletions of regions of the genome, miscarriage, or genetic disorders such as Down syndrome.  According to the study chromosomes from the mother (not including the X chromosome) averaged around 40 recombination events per gamete, and those from the father had only 26. The authors confirm a previous finding that older mothers have more recombination events in the transmission of their genome to their offspring, while the father’s age has no such effect.  For both sexes, the majority of crossovers occur at genetic “hotspots,” small regions where genetic exchanges are unusually common. Although the overall rate of hotspot use was similar between the two sexes, a subset of hotspots seems to be used mainly by one sex of the other.  Strikingly the pattern of hotspot used varied among individuals, but seemed to be passed on from generation to generation–a heritable difference potentially pointing to differences in the recombination machinery among individuals.  The study uncovered tremendous variation in recombination rates over all genomic scales considered and in particular heritable variation in hotspot use.  Further studies will reveal the genetic basis of recombination-rate variation and the selective forces governing the evolution of recombination rates.