How many people does it take to make an embryo? It may sound like a rather simple question or even bizarre riddle, but the recent announcement that British scientist have created an embryo with DNA from three people has caused a bit of a stir.
How is it even possible? Why was DNA from 3 people necessary, when the DNA from 2 people has, for the most part, worked well in generating Homo sapiens and their predecessors for millions of years (Leakey 1978)? Well, this new twist on fertilization has to do with mitochondrial DNA (mtDNA) and mutations that can lead to serious health problems in humans.
* Mitochondria: The Cell's Powerhouse *
The mitochondrion is a type of cellular organelle, and each cell of the body typically has hundreds to thousands of them. These microscopic organelles are the powerhouses that provide the energy to run our cells.
Mitochondria are the sites of cellular respiration, a series of reactions that turn food energy into ATP (adenosine triphosphate) energy. ATP is like the "cellular Euro" of energy currency; a molecule that can be used to drive many types of reactions within the cell. Since most of our ATP is generated by the mitochondria, the role of this organelle is absolutely vital to the viability of every cell in our body (Campbell & Reece 2005).
* What Does The Three-Parent Embryo Have to Do With Mitochondria? *
The "DNA-from-three" technique is a procedure that researchers hope may be used in the future, to produce embryos free of certain inherited diseases related to mitochondrial DNA. Mutations, or mistakes, in the mitochondria's genetic code can contribute to serious genetic disorders such as muscular dystrophy, epilepsy, strokes and mental retardation.
The British scientists first created normal embryos from the sperm of a man and egg of a woman (as per usual). However, the woman's egg contained defective mitochondrial DNA.
Humans inherit their mitochondria only from our mother. So, in order to fix the defective mtDNA, the researchers transplanted the existing embryo into an egg with no nuclear DNA (no genome) that had been donated from a second woman who had healthy mitochondria (BBC 2008).
* Inherited Mitochondrial Mutations *
Inherited changes in mitochondrial DNA (those passed on through the egg of the mother) can cause problems relating to growth, development, and function of the body's systems. These mutations disrupt the mitochondria's ability to generate ATP energy, and often involve multiple organ systems, particularly organs and tissues that require more energy (such as the heart, brain, and muscles). This new research may be a way of circumventing some of these devastating genetic disorders (National Library of Medicine).
* Sources *
BBC News (2008) "Three Parent Embryo Formed In Lab".
Campbell & Reece, Biology, 7th Edition, Pearson Publications.
Leakey, R. E., and Lewin, R. (1978) People of the Lake: Mankind and its Beginning. Anchor Doubleday.
National Library of Medicine, Mitochondrial DNA National Institute of Health, US Government.