by Josh Forman, Head of Science, Outreach & Education
On Wednesday 3rd July 2024, we were fortunate enough to hear insights from some world-renowned researchers and thinkers about the fascinating topic of Mitochondrial DNA in the latest instalment of Jnetics’ Scientific Lecture Series.
This DNA is little known outside of the genetics world, generally eclipsed by the far bigger, more variable and more studied nuclear DNA. In fact, of the approximately 20,000 genes that make up each human being, on 37 are found on the mitochondrial DNA.
We do not know with 100% certainty, why mitochondria even has its own DNA. It is the only organelle (component of a cell) that does. We think it is because, very early in the evolution of life on Earth, mitochondria were a separate bacterial species that could respire aerobically, using oxygen in the atmosphere to release energy. It then developed a mutualistic relationship with larger cells that could photosynthesise, i.e. produce their own food in the form of sugar from sunlight and CO2, and over billions of years, this relationship evolved to the extent that they merged and became one and the same.
They just kept some of their own DNA.
The most well-known use of mitochondrial DNA generally has been to track the evolution and movement of humanity through the maternal line. Mitochondria are only passed down through the mother, as they come from the egg, and mutate much slower than nuclear DNA. The mitochondria that power the sperm to get to the egg are discarded upon fertilisation, meaning no mitochondria are passed from father to offspring.
This means that we can track lineage through the maternal line via genetic variations in the mitochondrial DNA. This is the pathway that Dr Doron Behar, founder and CEO of Igentify, discussed with us during the Zoom webinar, and the fact that the entire Ashkenazi global population has come from 3 lineages – meaning 3 individual women. This is completely mind-blowing, yet also makes complete sense at the same time!
The fact that we can track lineage to this level of detail is phenomenal. It can also be used to demonstrate that the different Jewish ethnicities are more closely related, i.e. an Ashkenazi Jewish Brit is more closely related to a Persian Sephardi Jew, than a non-Jewish Brit. This really lends itself to the more general question of Jewish race and ethnicity versus religion, or a ‘people’, and are Jews actually European? I won’t wade into this potentially controversial topic here, but there is certainly food for thought.
Professor Joanna Poulton, Professor of Mitochondrial DNA at the University of Oxford, spoke about Mitochondrial Disease, the devastating impact of it, how inheritance works and what we can do about it.
Unlike the conditions that Jnetics screens for, Mitochondrial Disease is only passed from mother to child – due to mitochondrial inheritance being maternal. It is also an incredibly varied condition, ranging in both symptoms and severity. We now know that this is based primarily on the number of affected mitochondria in each cell, and in which cell. The next question from here is what determines how many and which mitochondria are affected? Plus, why does it very so drastically from mother to child?
Mitochondrial transfer is the newest, and potentially most effective, treatment for this condition. The concept behind this being that the nucleus of a fertilised egg is removed from the affected mother, so that the nuclear DNA is of the biological mother and father, and then implanted into an empty (i.e. nucleus removed) egg of a donor. This means that the embryo would have mitochondria from the egg donor, so that there is no risk of the disease.
This is still a very new procedure, with the only centre providing it in the UK in Newcastle. We do not yet know of the general outcome of patients of the technique, as it is too soon, and only approximately 5 children have been born using it.
Rabbi Weitzman of Machon Puah in Jerusalem then explained the Halachic considerations surrounding it. Ultimately, if this will save a life, we are duty-bound to do it. The more interesting conversation centres around who is the mother, and to what level does the DNA of a child impact this? Around 20% of the DNA in a cell, and thus an individual, is mitochondrial, simply because there are so many mitochondria in a cell. Therefore, the egg donor has contributed a significant proportion of the child’s lineage – how can this be considered?
If you would like to watch the webinar, please find it here on our YouTube channel.
For any further information, check out our website www.jnetics.org, or email info@jnetics.org.
