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The two cells produced at the end of the first stage of meiosis (meiosis I), each containing one chromosome from each homologous pair still joined to the sister chromatid.

Use in clinical context

In oogenesis, primary gametes are formed during embryonic development and they remain at this stage until puberty is reached at which point meiosis continues. It may take up to 45 years for the eggs in a woman to complete meiosis, whereas in a man the whole process takes only a few hours as sperm are produced all the time from puberty. This difference can explain why the chance of a baby having a chromosomal condition increases with the mother’s age.

Last updated on 31st May, 2019