Miscounting Chromosomes

Egg cells or oocytes have unique characteristics that make them different from other cells. One of the main differences is the number of chromosomes – condensed structures of DNA. Most human cells have 46 – 23 pairs – but eggs (and sperm) have only 23. This number is critical because any more or less can lead to infertility and miscarriages. These errors occur during meiosis; specialised cell division that generates egg cells, and these errors become more common as women age, but we didn’t know why. By imaging oocytes from younger women (left) and older women (right), researchers have found that a protein called Sgo 2 (green) is vital to helping the chromosome pairs to line up correctly before being pulled apart by microtubules (orange). In older women, Sgo2 doesn’t localise to the right locations meaning that the chromosomes are not lined up correctly for the big divide, increasing the chances of older eggs not meeting that magic number of chromosomes.

Written by Sophie Arthur

Sophie Arthur

former Science Communications Officer MRC LMS

Formerly a stem cell biologist, Sophie has since moved into science communication working at the MRC LMS. She also writes an award winning science and education blog Soph talks science.

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• Image from work by Bettina P Mihalas and colleagues
• The Wellcome Centre for Cell Biology, Institute of Cell Biology, University of Edinburgh, Edinburgh, UK
• Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Published in bioRxiv, January 2023 (not peer reviewed)