Fertilisation is arguably the most important point in our life. Egg and sperm unite pairing together one half of their chromosomes. Both cells have to lose half this genetic information to facilitate the process. Researchers can track the carefully orchestrated sequence of events in a mouse egg by injecting beads (shown in blue) that mimic the DNA. For the all-important separation step the DNA strands must be precisely positioned in the outer reaches of the cell (right). Long, spindle-like proteins (green), tease chromosomes apart inside an awning of sorts at the cell surface. The proteins then rotate leaving half of the DNA in the awning. Other proteins (here coloured red) encourage the awning to break away with the doomed strands. If the chromosomes are wrongly positioned (left and middle), separation begins, but ultimately stalls before they can be extruded.
Written by Hayley Birch
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