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Life Science: Session 3

Cloning

What is cloning?

DNA insertion
DNA inserted into egg for cloning

Cloning is a type of reproduction where the offspring is genetically identical to the parent. Cloning has become a topic that periodically receives attention in the news, with most people correctly understanding it to be a type of reproductive technology. However, cloning occurs all the time in nature. Not all organisms reproduce sexually. In fact, most single celled organisms reproduce asexually and many plants and animals can reproduce asexually as well. How does this occur? In these organisms, clones are formed in the same way that body cells are formed: The entire genome in a parent cell is duplicated and passed to two daughter cells, resulting in two identical individuals. In this way, body cells are actually clones of one another. While this can be advantageous in terms of not having to spend energy producing sex cells or locating a mate, the offspring lack the genetic variation observed in sexually reproducing organisms.

How are clones formed through reproductive technology?

Dolly
Dolly, the cloned sheep

In 1998, the world learned of the first successful example of a mammal cloned from an adult cell. This was Dolly, undoubtedly the world’s most famous sheep. Dolly was formed by extracting a donor cell from an adult sheep and implanting it into an unfertilized sheep egg that had its DNA removed. The donor cell, with its DNA-containing nucleus, was stimulated by pulses of electricity to induce it to fuse with the egg cell. The result was an egg that contained the entire genome of the adult donor — without ever involving the process of sex cell production and fertilization. Under specific conditions, this cell began to divide, and the resulting embryo was implanted into the uterus of a surrogate mother sheep. Dolly was the result. This is essentially the same process used for other cloning endeavors.

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