D: Last time we were talking about how cloned animals, to some people's surprise,      aren't just copies of their parent animals. In cloned pigs, for example, some come out      bristly-haired, some smooth; some are shy, others aggressive.

Y: How can animals share all the same genes and yet be so different?

D: Geneticists aren't sure yet. One possibility is that chemical conditions inside the uterus      affect how the fetus develops. But there's also gene expression to consider.

Y: Gene expression?

D: That just means which genes are turned on and which are turned off.

Y: Oh, I see...no, I don't. Better explain that.

D: Well, every gene in your body comes in duplicate. You got one from your mother      and one from your father. Let's simplify the situation and pretend there's just one      gene that gives you your sparkling personality.

Y: I know I got that from my mother--my dad was a crank.

D: In this instance, then, we can imagine that the "personality gene" your father gave you      is in the "off" position, while the personality gene your mother gave you is in the "on"      position. Would a Yaël clone have your same personality? We don't know, because      we don't know what position that switch will be in. And in reality there are many,      many switches, leading to many possible combinations.

Y: I think I see now. A clone is a duplication of the genes, but not of the gene      expression. So my clone could share my genes and still look and act differently.

D: Exactly. Clones aren't carbon copies--they are separate organisms all to themselves.  

To hear this program click here

A Moment of Science®