cloning

cloning

Cloning is the process of creating an exact genetic replica of an organism. The clones DNA is exactly the same as the parents DNA. Bacteria and other single-celled organisms have long been able to clone themselves through asexual reproduction. Plants can also reproduce asexually. In animals, however, cloning does not happen naturally. In 1997, that all changed when a sheep named Dolly was the first large mammal ever to be successfully cloned. Other animals can now also be cloned in a laboratory. The process of producing an animal like Dolly starts with a single cell from the animal that is going to be cloned. Below are the steps involved in the process of cloning: 1. In the case of Dolly, cells from the mammary glands were taken from the adult that was to be cloned. But other somatic cells can be used. Somatic cells come from the body and are not gametes like sperm or egg. 2. The nucleus is removed from this cell. 3. The nucleus is placed in a donor egg that has had its nucleus removed. The nucleus must be removed from the donor egg to maintain the appropriate chromosome number. 4. The new cell is stimulated with an electric shock and embryo development begins, as if it were a normal zygote. The zygote is the first cell of a new organism. 5. The resulting embryo is implanted into a mother sheep, where it continue its development ( Figure 1.1). To clone an animal, a nucleus from the animals cells are fused with an egg cell (from which the nucleus has been re- moved) from a donor, creating a new zy- gote.

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is cloning easy

Cloning is not always successful. Most of the time, this cloning process does not result in a healthy adult animal. The process has to be repeated many times until it works. In fact, 277 tries were needed to produce Dolly. This high failure rate is one reason that human cloning is banned in the United States. In order to produce a cloned human, many attempts would result in the surrogate mothers experiencing miscarriages, stillbirths, or deformities in the infant. There are also many additional ethical considerations related to human cloning. Can you think of reasons why people are for or against cloning?

instructional diagrams

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questions

sperm and eggs are somatic cells.

a. true

-->  b. false

a sheep was the first large mammal cloned.

-->  a. true

b. false

which statement is correct?

a) to clone an organism, the nucleus from a gamete cell is placed in a donor egg.

b) to clone an organism, the nucleus from a somatic cell is placed in a donor sperm.

-->  c) to clone an organism, the nucleus from a somatic cell is placed in a donor

d) to clone an organism, the nucleus from a sperm cell is placed in a donor egg.

which best defines a zygote?

-->  a) the first cell of a new organism.

b) a cell that results from placing the nucleus into an egg cell.

c) a somatic cell isolated from an organism.

d) a gamete cell, such as a sperm or egg cell.

why must the nucleus be removed from the donor egg cell during the cloning process?

a) so the zygote does not have too many chromosomes.

b) to keep the number of human chromosomes at 46.

c) so the initial cell acts as a true zygote.

-->  d) all of the above are valid reasons.

which organisms can naturally create clones of themselves?

a) bacteria

b) single-celled protists

c) some plants

-->  d) all of the above

which is an example of a somatic cell?

a) a sperm cell

b) a zygote

-->  c) a mammary gland cell

d) all of the above

diagram questions

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