We start life as a single cell, created when dad's sperm meets mum's egg cell. The fertilised egg has a complete set of DNA, half from mum and half from dad. In order to create eggs and sperm that carry only half a set of DNA, specialised germ cells go through a process called meiosis. Here, a female mouse germ cell is in the final stage of meiosis. Shown in pink, the DNA is about to be divided to create a large egg cell and a much smaller cell called a polar body, which sticks to the side of the egg and plays no part in making a baby. This uneven division ensures that the cell destined to be the egg gets the biggest share of nutrients, to fuel the early stages of development. Researchers are studying how this process is controlled, to gain insights into the earliest stages of life.
Written by Kat Arney
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