In What is cloning? we learned what it means to clone an individual organism. Given its high profile in the popular media, the topic of cloning brings up some common, and often confusing, misconceptions.
Misconception #1: Instant Clones!
Let's say you really wanted a clone to do your homework. After reviewing What is Cloning? and Click and Clone, you've figured out, generally, how this would be done. Knowing what you know, do you think this approach would really help you finish your homework...this decade?
A common misconception is that a clone, if created, would magically appear at the same age as the original. This simply isn't true. You remember that cloning is an alternative way to create an embryo, not a full-grown individual. Therefore, that embryo, once created, must develop exactly the same way as would an embryo created by fertilizing an egg cell with a sperm cell. This will require a surrogate mother and ample time for the cloned embryo to grow and fully develop into an individual.
Misconception #2: Carbon Copies!
Your beloved cat Frank has been a loyal companion for years. Recently, though, Frank is showing signs of old age, and you realize that your friend's days are numbered. You can't bear the thought of living without her, so you contact a biotechnology company that advertises pet cloning services. For a fee, this company will clone Frank using DNA from a sample of her somatic cells. You're thrilled: you'll soon have a carbon copy of Frank - we'll call her Frank #2 - and you'll never have to live without your pal! Right?
Not exactly. Are you familiar with the phrase "nature versus nurture?" Basically, this means that while genetics can help determine traits, environmental influences have a considerable impact on shaping an individual's physical appearance and personality. For example, do you know any identical twins? They are genetically the same, but do they really look and act exactly alike?
So, even though Frank #2 is genetically identical to the original Frank, she will grow and develop in a completely different environment than the original Frank or will have a different mother, and she will be exposed to different experiences throughout her development and life. Therefore, there is only a slim chance that Frank #2 will closely resemble the Frank you know and love.
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Here, kitty, kitty
On December 22, 2001, a kitten named CC made history as the first cat - and the first domestic pet - ever to be cloned. CC and Rainbow, the donor of CC's genetic material, are pictured below.
But do you notice something odd about this picture? If CC is a clone - an exact genetic copy - of Rainbow, then why don't they look exactly alike?
The answer lies on the X chromosome. In cats, a gene that helps determine coat color resides on this chromosome. Both CC and Rainbow, being females, have two X chromosomes. (Males have one X and one Y chromosome.) Since the two cats have the exact same X chromosomes, they have the same two coat color genes, one specifying black and the other specifying orange.
So why do they look different?
Very early in her development, each of Rainbow's cells "turned off" one entire X chromosome - and therefore, turned off either the black color gene or the orange one. This process, called X-inactivation, happens normally in females, in order to prevent them from having twice as much X-chromosome activity as males. It also happens randomly, meaning that not every cell turns off the same X chromosome.
As a result, Rainbow developed as a mosaic of cells that had one or the other coat color gene inactivated - some patches of cells specified black, other patches specified orange, and still others specified white, due to more complex genetic events. This is how all calico cats, like Rainbow, get their markings.
CC looks different because the somatic cell that Rainbow donated to create her contained an activated black gene and an inactivated orange gene. What's interesting is that, as CC developed, her cells did not change that inactivation pattern. Therefore, unlike Rainbow, CC developed without any cells that specified orange coat color. The result is CC's black and white tiger-tabby coat.
Rainbow and CC are living proof that a clone will not look exactly like the donor of its genetic material.
For more information about CC, Rainbow, coat color and X-inactivation, see Additional Resources.