• Question: Why is the mitochondria only passed on by the X chromosome

    Asked by charlieduffy on 15 Nov 2021.
    • Photo: Amy Holt

      Amy Holt answered on 15 Nov 2021:

      Mitochondria are not linked to the X chromosome, they actually have their own DNA which is separate to the 23 pairs of chromosomes that are found in the cell nucleus.

      Mitochondria and their DNA are only inherited from your mother because the egg cell contains all of the mitochondria that will be present in the developing embryo. When the sperm cell fertilises the egg, the mitochondria from the sperm don’t remain in the embryo.

      It’s not completely clear how/why this happens, there’s a good article about it here: https://www.nytimes.com/2016/06/24/science/mitochondrial-dna-mothers.html

    • Photo: Thomas Nicol

      Thomas Nicol answered on 15 Nov 2021:

      Mitochondria are not passed on by the X chromosome, rather they are inherited with the egg. In mammals this means that mitochondria are maternally inherited. Sperm have their own mitochondria but they are not typically transferred to the egg upon fertilisation.

    • Photo: Magdalena Sutcliffe

      Magdalena Sutcliffe answered on 15 Nov 2021:

      Inheritance of mitochondria is independent of the rest of the genetic material. Chromosomes sit inside the cell nucleus and fusion of nuclei from a mother’s and a father’s gamete (reproductive cell) produces a complete set of chromosomes needed for the new human to develop. But the mother’s gamet, the egg, also contributes the “filling” of the cell (cytoplasm) that contains all the machinery needed for the cell to function. The cytoplasm contains mitochondria and that’s why the baby only inherits them from the mother.
      Because of this it was recently possible to make a baby with 3 parents, where one woman contributed the chromosomes and another one the egg cytoplasm with mitochondria. The father contributed the other part of the chromosomes.

    • Photo: Madeleine Heep

      Madeleine Heep answered on 19 Nov 2021:

      Mitochondria are not passed on by the X chromosome, but you do get your mitochondria from your mum. When an egg inside a woman gets fertilized, it passes on some components (like the mitochondria) to the baby.

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