Ed’s note: The author of this post is Andrew, a Cell Biologist (more information at the bottom).
Every so often, a discovery is made, a technology is developed, or a news item comes out that seems to be tailor-made for misleading descriptions. From evolution’s “missing link” to the metamaterials “Harry Potter invisibility cloak,” some things just beg to be oversimplified and hyped-up. The FDA is considering a new technique that has been all over the news, and fits nicely into this category: Three-Parent Babies. If you don’t quite get the science behind this technique, I’m going to try to give an overview of what is happening address some of the misconceptions.
Intro Bio Background:
A typical human has 46 chromosomes, organized into pairs. When a sperm or egg cell is made, it gets one copy from each of those pairs, resulting in 23 chromosomes. It’s not a truly random assortment—the chromosomes don’t get mixed up and 23 random ones chosen, for example. Each sperm and egg cell get one chromosome from each pair (this will be important later).
With normal fertilization, a sperm cell from the father meets an egg cell from the mother, and you get an embryo (bow-chicka-wow-wow). The sperm cell is just a delivery system for the father’s chromosomes, with a flagellum, some enzymes, and a bunch of mitochondria—virtually all of which fall away after it delivers its genetic material. The egg cell is where all of the “other stuff” is—it’s a giant cell, full of proteins, enzymes, membranes, and organelles (including mitochondria).
This technology simply introduces a third person to provide part of the egg. A third person donates an egg, and its nucleus is removed. An egg is taken from the mother and its nucleus is transferred into the donor’s egg. It gets fertilized by sperm from the father, becomes an embryo, and from that point on, it’s normal IVF. In effect, the egg that gets used comes from two people – its nucleus is from the mother, and the cell with all of the other “stuff” comes from the third donor.
The “stuff” is the important part. Among other things, it contains mitochondria. They’re the power plant of the cell, but they’re unusual because they have their own DNA. It’s left over from when they used to be free-floating bacteria, before they evolved into a symbiotic relationship with our single-celled ancestors. Since they have their own DNA, they can have their own mutations, which can, in turn, lead to a whole bunch of problems. The result of this technology is to allow a couple to reproduce mostly with their own genes but “replace” the faulty mitochondria.
Since mitochondria have their own DNA, they can suffer from mutations that can to serious detrimental effects, such as blindness, deafness, neurological problems, and metabolic diseases. Like many genetic diseases, these problems can be debilitating, life-threatening, and extremely difficult to treat. While this technology can’t be used to treat mitochondrial disorders, it can be used to allow affected individuals to have children without the risk of passing the disorder on to them.
The big misconception is right in the name of the technology: Three-parent babies. That gives the impression that embryos are being produced with a 1:1:1 contribution from all three parents. It’s kind of inaccurate to say that these are three-parent babies though, since all that comes from the third parent is the mitochondria. Humans have something like 20,000 genes—and since chromosomes are in pairs, those genes are in duplicate. Mitochondria have 37 genes. That comes out to 0.09% from the “third parent.”
I don’t think we’re anywhere near being able to make true blends of multiple parents. When a cell divides, its chromosomes sort themselves out by finding their pair (by certain regions of DNA sticking to each other) and lining up along the center of the cell. Microtubules form, attach to each one of the chromosomes, and pull to opposite sides of the cell. This splits up the chromosomes, making sure that each cell gets one from each pair. This works great on the microscopic scale inside the cell, but it’s not really something that we can do by hand. Chromosomes are only visible at a certain stage of cell division, and it doesn’t last very long (we can chemically “pause” it, but this comes with its own problems). Chromosomes are also too tiny for us to manually move around, and even if we could, we don’t have any way of identifying chromosomes without chemically modifying them—there’s no way of knowing whether you’re looking at Chromosome 1, Chromosome 2, Chromosome 3, etc., without taking them all out and chemically modifying them.
This is important, because a healthy human doesn’t just need 46 chromosomes—they need 23 pairs of specific chromosomes. In order to make true three-parent babies, you would need to be able to positively identify each chromosome, and then have a method to isolate it and move it around. The technology we’re looking at now doesn’t need that level of finesse. It simply takes the nucleus from one cell (which already contains the necessary chromosomes, and is big enough to move around with a fine needle) and pops it into another cell.
As a final note, I don’t think that this technology falls under the category of “designer babies.” We’re not talking about mixing and matching different traits, or modifying genes. It simply replaces all of the mitochondria from the mother with mitochondria from the third donor. All 37 of those genes come over as a bundle. If anything, I’d call this more of a transplant than real design or engineering. Calling it genetic engineering or “designer babies” would be like calling me a fashion designer by virtue of the fact that I can pick a pair of pants and a shirt out of my dresser that (usually) don’t look terrible together.
So, in case you’re in a TL;DR type of situation, but you’re somehow still reading my last paragraph, here’s the recap:
- This technique doesn’t result in true 3-parent babies, since the baby gets 22,000 genes from the father, 22,000 from the mother, and 33 from the 3rd donor. It’s more like 2.0009-parent babies
- This technique can’t be modified to make multi-parent babies, since we’re nowhere near being able to manipulate individual chromosomes to the necessary extent.
- The resultant neonates are not “designer babies” since the only change from normal IVF is that faulty mitochondria from the mother get swapped out with healthy mitochondria from an egg from a female donor. The mitochondrial genes are only 0.09% of the child’s final genome, and the parents can’t pick and choose what genes come over—it’s all or none of the mitochondria from the third donor.
Author Bio: Andrew is a cell biologist who spends his days in a molecular biology lab teaching students and nights painting miniatures and tending his ongoing biology experiment, a.k.a. his daughter. (He is also Mary’s husband, affectionately referred to as Spousal Unit 3000.)