Stardate 20020131.1244

(On Screen): A group of researchers working with eggs from female monkeys have managed to chemically stimulate them to cause a few of them to start dividing without being fertilized. Beginning with 77 eggs, four reached the level of a blastocyst. Working with those, the researchers then extracted stem cells and managed to convert those into mature tissues of various kinds.

It's scientifically interesting, but I'm not sure it is of any important medical use. The article talks about it as a way of creating transplant organs, and mentions that such organs could only be used by the woman who donated the eggs in the first place.

Actually, I'm not sure even that would work.

Like all germ cells, eggs are haploid, with 23 chromosomes. With normal fertilization a haploid sperm cell will contribute an additional 23 chromosomes, and the resulting fertilized egg will be diploid, with the normal complement of 46 chromosomes.

The treatment given to the unfertilized eggs must have caused them to do a partial cell division which was incomplete. The 23 chromosomes reproduced, yielding 46, but the cell did not divide. Thus the egg converted from haploid to diploid without fertilization.

But the resulting cell would not be genetically identical to the cells of the donor. It would carry two copies each of 23 of her chromosomes, and no copies at all of the other 23.

So, for example, if she had type A blood but was heterozygous for that character, it's possible that the parthogenetically created diploid cell might carry two copies of her type O gene, and none of her type-A gene. If a stem cell were used to create blood, it would be type O blood. The same would go for many other characters. It's not clear that tissue grown from that egg would be any more compatible with her than would tissue from a close relative. It would be an antigen subset rather than an antigen match, and we don't know if that works properly.

And there's another problem: the parthogenetically created egg would be 100% homozygous for every single gene, since each pair of chromosomes would be copies. All of us carry numerous recessive genes which are harmful, but they don't express because we are heterozygous. But every single negative recessive gene among the 23 chromosomes in the original egg would double, and would express. The phenotype of the resulting tissue would be deeply flawed.

I can't see how this development can have actual clinical value.