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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?
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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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