Map of life expectancy at birth from Global Education Project.

Wednesday, September 28, 2016

Brave New World?

There has been a lot of yammering but very little explanation or understanding of the baby recently born to a Jordanian couple which is purported to have "three parents." The technique which made this possible is illegal in the United States and apparently for some reason offensive to many people.

The baby does not have three parents, he has two. What he also does not have is Leigh's disease, which is the whole reason the procedure was done. But in order to really understand what happened, you need to understand something about the history of life on earth, which was not created in seven days 10,000 years ago.

Some time around 2 billion years ago (no way to be at all exact) one cell absorbed a smaller one, which survived and reproduced inside it and so the smaller cell's descendants continued to inhabit the larger cells descendants after the larger cell divided. The two cell types then evolved together as a symbiotic community. The smaller cell gradually lost most of its genetic material (some of it may have migrated to the nucleus of the larger cell) and was reduced to specialty functions, most notably as the manufacturer of Adenosine Triphosphate, the cell's energy source. The DNA that remains in the mitochondrion is only what is needed for mitochondrial functioning. It has not influence on the development or characteristics of the organism beyond any effect of defective mitochondrial functioning, an example of which is Leigh's disease.

The nuclear DNA is the DNA that combines chromosomes from the mother and father, and determines everything else about our genetic inheritance. The mitochondria are inherited exclusively from the mother through the cytoplasm of the ovum. You could vacuum out all the healthy mitochondria from a fertilized ovum (gamete) and replace them with equally healthy mitochondria from a different, completely unrelated person and the resulting human would be completely unaffected.

In this case, the mother had some healthy mitochondria and others that had a fatal mutation. She had enough healthy ones that she was not ill, at least not seriously; but there's no telling what the proportion of functional and non-functional mitochondria will be in any of her ova. Unfortunately, she'd had the bad luck to have two babies who were severely affected and who died young. What the doctors did in this case was simply to transplant the nucleus from one of her ova into another woman's ovum from which the nucleus had been removed, and fertilize it with her husband's sperm. Result: baby with two parents and no mitochondrial disease.

It had to be done in Mexico because it's illegal in the U.S. I await an explanation of why this is unethical.

1 comment:

robin andrea said...

I read an article about this yesterday and found the science of it utterly fascinating. I have absolutely no objections whatsoever about such an amazing feat of science. I did however wonder why humans would spend so much time trying to make one baby happen when there are already seven billion humans on our over-crowded planet and plenty of babies who need loving good homes.