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Is it possible for two humans (or animals) of the same sex to have (viable and biological) offspring? By either fusing two haploid cells, or extracting chromosomes from one haploid cell and inserting them into the nucleus of another and (in both cases) induce fertilization? Also, is there any (legal) way to test this? And if so, what is the process?
Question Date: 2002-11-17
Answer 1:

What an excellent question! The fact that you are asking this in only the tenth grade is especially impressive, and is a testimony to yourself, your teacher, and the rapid progress of molecular biology.

I'm not particularly knowledgeable in this field, but my first impulse is to say that, yes, this seems possible.

Certainly if we have the ability to grow a clone using DNA derived from a somatic cell, it should be possible to do the same using reproductive material. Both of the methods you described seem feasible. For two females to reproduce, taking the haploid DNA from one egg and using it to fertilize the other would seem like the most straightforward approach. Of course, with two females only female offspring would be possible (at least in the case of humans). For two males to reproduce, some egg material would be necessary, so this would have to approximate a more traditional cloning exercise, but involving the removal of two sets of haploid DNA for insertion into a vacated egg. This procedure would be more complex and thus less likely to be successful, but probably not impossible. Also, with two human males it should be possible to produce male or female children.

Of course, while the theory seems sound, in application actually pulling it off is quite another matter. On reflection it's hard to believe that this hasn't been tried yet, but if such a procedure were successfully performed it would certainly have made some headlines, so maybe it really hasn't been done. Hopefully somebody who's more familiar with this field can give you a better answer. Otherwise, I say go for it! (Just not with humans).

Answer 2:

This is a tough question. It reminded me of a question someone asked a while ago about whether a male could produce sperm with another individual's genes. (You can see that answer at scienceline Just do a search using "sertoli" as a key word.)

Your question is similar in some ways because it's about trying to get cells to form an embryo in a way that they usually don't. Let's look at what each gamete (sex cell) contributes to make an embryo. You already know that each is haploid and contributes half of the genes needed. The egg cell supplies the organelles, cytosol (cell fluids), and cytokeleton. In addition to genes, the sperm supplies the centrosomes, which are vital to allowing the fertilized egg to divide. As I understand it, the centrosomes are lost from the egg cell and put into the final polar body (along with the excess DNA). So a vertebrate cell can't divide until it's fertilized.

So let's say one were to take an egg, insert the DNA from another egg, and then insert centrosomes from another cell, would the cell divide? Well, you might have to give it a mild electric shock to start division. That's what they do in some cloning techniques. There's still no guarantee it would work, but at least the pieces would be there. As for the two-sperm question, it seems like an egg would be needed too, in order to supply organelles and other inside things along with the outside covering of the egg (follicle) .

But let's say the nucleus were removed from the egg, a sperm's nucleus were implanted in the egg, then sperm were allowed to fertilize the egg. Could it work? Maybe. There's so much we still don't know about "standard" fertilization that it's tough to say.

About the question of legality, there are laws requiring humane treatment of animals in research. If they were followed, doing this research on mice, frogs, etc. would probably be legal. If you're asking about people, it's obviously a lot more complicated. There would be a lot of controversy, but I don't know whether it would be legal or not. Is the genotype (genetic code) of each gamete a person makes the same? If you're not sure, think about crossover.
Thanks for asking,

Answer 3:

I want to complement you, Elena, for such thought provoking question. I would give you an A just for such critical thinking. My students ask questions like: Do I have to read the book? Will it be in the test?

I had lunch with my three genetics colleagues and we discussed your question. I will attempt to answer it in the following way:

The answer is "YES" theoretically, it is possible for two humans (or animals) of the same sex to have offspring. If we understand all the intricacies of biological events, they can be replicated in the lab. The problem is, that we still do not understand much of gene regulation and reproduction.

In 1997 the news of "Dolly" the sheep caused headlines throughout the world. Dr. Ian Wilmut and his associates at Rosalind Institute, England did what many scientists thought was impossible. They cloned a mammal, using the nucleus (diploid) from an adult tissue and placed it in the egg cell whose nucleus was removed. This process is called "Nuclear Transfer".

Today, besides sheep, we have cloned monkey and cat. Here a diploid nucleus is used, therefore it is asexual reproduction. No one has successfully replicated this in a normal human cell. Once this process is refined and we understand all the gene regulation, it can be done in humans. This will provide an option for lesbian couple to have a child. The donor partner will contribute all the 46 chromosomes. The recipient will contribute its mitochondrial DNA, which is a very small amount of extra chromosomal DNA, less than 1%. The recipient partner will carry the child and provide the child with nourishment.

Unlike in case of IVF where the egg and sperm come from two different sources, in gay couples, one can contribute a sperm, and the partner will be left out. Some unsuccessful attempts have been made to fuse two haploid cell from same sex individuals and it never resulted in fertilization or implantation. One of the explanation is that there is a phenomenon known as genetic imprinting. The research on human germ cell and embryo is not allowed in this country. Even if it were to be allowed, the success rate will be not very good.

Dolly was the result of 1 out of 277 fusion (many hours/days/years/dollars). Not a very good success rate. Dolly is already showing signs of early aging. Lets assume that we are successful in fertilizing two haploid nucleus from two separate females. What can we predict about the offspring? There are many diseases that have been diagnosed, they are result of uniparental disomy: a condition where a particular chromosome comes from the same parent.

For example, when both chromosome # 15 comes from mother, the child is born with a genetic disorder called Prader Willi Syndrome and when both # 15 comes from father, it causes Angelman Syndrome. Later it was discovered, that it was not the whole # 15 that was causing the problem, but a single gene that came from mother or father. So if one gene from same sex can cause this much problem, what will happen when all the genes were maternal or paternal? This is what we call the Genetic Imprinting. The questions we should ask are: Why would we do this? Who would pay the cost? Who will benefit from the technology? and etc.

While we say that theoretically every thing is possible, it does not mean that every thing should be done and pursued unless we have good reasons to justify such expense.

Answer 4:

You have essentially described "cloning by nuclear transfer". In the case of Dolly the sheep, and more recently many other mammals, "clones" have been produced in the following (simplified) way:

1. isolate an egg, and remove its nucleus (genetic material)
2. isolate the nucleus of a somatic cell (say, from the mammary gland) and insert it into the enucleated egg.
3. "activate" development (by electrical shock and calcium, essentially mimicking the act of fertilization).
4. Allow the embryo (which now has a nuclear genome identical to the mammary gland cell donor) to develop to an early embryonic stage, then implant it into a surrogate mom's uterus.
5. Carry embryo--> fetus to term and deliver a new "baby" animal that is a genomic clone of the animal that donated the mammary gland cell.

Another variation on the theme is actually fusing a diploid somatic cell with an enucleated oocyte (as opposed to moving just the nucleus).

This type of "cloning" is now pretty common in mice and some other vertebrates. In humans, of course, this is illegal. There are many ethical considerations, but even beyond the ethics is the issue of success rate and viability of offspring. The success rate (% embryos that make it to term) is very low and there is increasing evidence that offspring produced in this manner have some genetic differences that may be problematic. A high percentage of cloned mammals tend to be born large and then are obese (and perhaps may have some other problems as well). We do not know why. We do not really understand the basic mechanism of genetic reprogramming that occurs in eggs (and stem cells) so "successful cloning" is really just hit or miss.

Consider this: Dolly, the sheep, was the first mammal cloned in this way. An enucleated egg was provided with a diploid nucleus from a cell taken from the mammary gland of a 6 year old ewe. How old, then, is Dolly? Is her age based on the time she was born or based on how old her DNA (genetic material) is ; i.e. 6 years older than her actual chronological age? As you might imagine, studying cloned animals can be useful for studying cellular/genetic aging mechanisms.

You can find out more about the science and ethics of cloning by nuclear transfer, somatic cell fusion and stem cell cloning by visiting the website of the National Institutes of Health National Institutes of Health . Be careful of any web based information other than on validated, referenced sites -- there is a tremendous amount of misinformation and disinformation out there (as you might imagine given that it is such a crucial issue).

Recommended reading:

"Clone. The Road to Dolly and the Path Ahead." by Gina Kolata.
"Dolly and the Age of Biological Control." by Wilmut, Campbell and Tudge.

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