In vitro fertilisation, or IVF, is the last hope for infertile couples hoping to have children, but the technique is fraught with complications. Many embryos are rejected, as they develop defects; for example, mosaic embryos contain some cells with abnormal numbers of chromosomes, a condition known as aneuploidy. By observing developing mouse embryos, like the one pictured, researchers have recently uncovered a possible explanation for this problem. When cells multiply, they duplicate their genetic material, then carefully distribute copies of each chromosome into their daughter cells. Any mistakes can cause the formation of micronuclei, structures containing isolated chromosomes, which are not correctly allocated during subsequent cell divisions. In developing mice, and most likely in humans too, this leads to embryos with cells containing different numbers of chromosomes. Understanding how these mosaics arise may help ensure more embryos develop without defects, hopefully increasing the chance of success for IVF patients.
Written by Emmanuelle Briolat
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