Answer to Critical Thinking Activity - Chapter 21

1. Twinning is done when undifferentiated cells from a very early developing embryo are separated in the laboratory, properly cultured or otherwise taken care of, and each one develops into a fully formed organism. This is no different from the natural process wherein the egg naturally divides in two, or three, four, or more, to produce twins, triplets, etc. All the cells of the body contain a complete copy of the genetic material of an individual, but, as time passes, they differentiate into skin cells, liver cells, etc. True cloning would take place when a differentiated cell is triggered into developing into a complete copy of an organism.

2. Yes. Refer to the article on sheep cloned by nuclear transfer from a cultured cell line.

3. This is a question you must answer for yourself. Problems that arise in answering this question involve such things as when does a human embryo become human? Does it become human the instant the sperm fertilizes the egg? If not, exactly at what stage of development does it become fully human? My personal answer here is: no.

4. Again, this is a question you must answer for yourself. The article, SHOULD WE CLONE ANIMALS, has some excellent thoughts on this. However, my personal answer to this question is: for good and proper reasons we may clone animals. The problem that now appears is: exactly what are good and proper reasons? Not everyone is going to accept mine, nor will I accept all those of others. Some will accept none. And so the argument goes.