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Cloning
What is cloning?
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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?
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Dolly, the cloned
sheep
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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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Cloning
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