A clone is a genetically identical copy

[NMencia09]

A clone is a genetically identical copy of a living organism. Human clones are nothing new; they occur naturally in the recognizable form of identical twins. Not until the successful cloning of a sheep called Dolly, however, has the possibility of intentionally producing an identical copy of a human been considered seriously.
Production of a human clone would most likely utilize the same basic methodology that resulted in Dolly. A human egg would be retrieved from an individual, and its genetic material (DNA) would be removed and replaced with DNA derived from any adult human cell type. This would bypass the need for fertilization of the egg by the sperm in order to obtain a full complement of DNA. In a laboratory dish, the egg would then undergo several cell divisions. Placed into a uterus, the resulting embryo would grow and, with luck, develop until birth.
Although this cloning technique is conceptually and procedurally simple, its success rate has been extremely low. The birth of one Dolly, for instance, required the preparation of 277 re-nucleated eggs, followed by the implantation of 29 resulting best embryos. The low success rate can be attributed to the difference between the young DNA of a normally fertilized egg and the genetic material of the re-nucleated egg, which is mature and of defined destiny - it has already committed itself to a particular physiological role. In order for proper fetal development to occur, mature DNA must be coaxed into reverting to its youthful state, a complex process that will be difficult to achieve for the human species.

The passage suggests which of the following?


Human cloning is reachable within ten years.

The cloning of nonhuman animals has always been successful.

The eggs of nonhuman animals are easier to obtain than human eggs.

DNA taken from an adult human cell contains DNA from both parents.

Human DNA is less predictable than nonhuman DNA.

Answer is (D), I chose (E). Passage doesn't explicitly mention 'DNA from both parents'. Also, cloning for Dolly was possible, whereas that of humans is a 'complex process that will be difficult...' . I guess I kind of thought that since it was done for Dolly and its seen as relatively more complex for humans, the predictability of the DNA is one of the issues which makes human cloning more complex.

Any thoughts? many thanks.

[jnelson0612]

Here's the part that justifies D:
A human egg would be retrieved from an individual, and its genetic material (DNA) would be removed and replaced with DNA derived from any adult human cell type. This would bypass the need for fertilization of the egg by the sperm in order to obtain a full complement of DNA.

E is close; I see your point, but the passage tell us that human cloning is more difficult than animal cloning. We can't assume that the DNA is less *predictable*.

Tough stuff!

[thapliyalabhi]

Here's the part that justifies D:
A human egg would be retrieved from an individual, and its genetic material (DNA) would be removed and replaced with DNA derived from any adult human cell type. This would bypass the need for fertilization of the egg by the sperm in order to obtain a full complement of DNA.

E is close; I see your point, but the passage tell us that human cloning is more difficult than animal cloning. We can't assume that the DNA is less *predictable*.

Tough stuff!

I understand that the bold part above somehow suggests that DNA from adult cell contains DNA from egg(mother), but how does it indicate that DNA from adult cell contains DNA from the sperm(father). It says "this would bypass the need for fertilization of the egg by the sperm", which somehow indicates that sperm might not be used for fertilization. And the passage does not mention any other use of sperm here. Or, is it that we should assume "DNA derived from any adult human cell type" as the DNA from sperm(father).

Please clarify.

[jnelson0612]

Here's the part that justifies D:
A human egg would be retrieved from an individual, and its genetic material (DNA) would be removed and replaced with DNA derived from any adult human cell type. This would bypass the need for fertilization of the egg by the sperm in order to obtain a full complement of DNA.

E is close; I see your point, but the passage tell us that human cloning is more difficult than animal cloning. We can't assume that the DNA is less *predictable*.

Tough stuff!

I understand that the bold part above somehow suggests that DNA from adult cell contains DNA from egg(mother), but how does it indicate that DNA from adult cell contains DNA from the sperm(father). It says "this would bypass the need for fertilization of the egg by the sperm", which somehow indicates that sperm might not be used for fertilization. And the passage does not mention any other use of sperm here. Or, is it that we should assume "DNA derived from any adult human cell type" as the DNA from sperm(father).

Please clarify.

The passage is basically saying that if you want to make a human clone you have to take an egg, strip out the genetic material in the egg, and then replace it with with the DNA from any human cell. So the genetic material in the egg and the DNA from the human cell must be two different things. The DNA from the human cell must contain something that the egg by itself does not.

Now, focus in on the second part that I have bolded:
(by doing this replacement of DNA from the human cell into the stripped egg) . . . This would bypass the need for fertilization of the egg by the sperm in order to obtain a full complement of DNA.

So an egg contains the mother's genetic material
Once it is fertilized by a sperm it then has a "full complement of DNA".
"full complement" implies that it then has the regular amount of DNA seen in a person.
The whole thing implies that the sperm DNA is necessary to have the regular amount of DNA.

Does this make sense?