Well, the answer is mutations.
Mutations are often defined in textbooks as a changed DNA sequence.
But very importantly, I'd like to emphasize they are the ultimate source
of all genetic variation on the planet.
Because again, if we have a single origin of life, which we do assume, single origin
of life, common ancestry of all existing life, then all the diversity we see has
to come from iterations of mutation from that original self-replicating form, okay.
So, what is a mutation or what is a mutant?
I mean you hear this word often, both in common parlance and in the movies,
things like that.
Well, a mutant may be what you call your brother when he's being very annoying.
Get off me you mutant!
I heard that many times.
Those of you who are fans of science fiction, a mutant in the comic world is
an individual who possesses a genetic trait called an X-gene that allows
them to naturally develop superhuman powers and abilities.
So this is, there's a picture here form the comic X-Men.
You may have seen the movies from that.
Probably not the definition we'll be using here in this class, as you'd guess.
You make think of a mutant as
someone who has an extreme disfiguration such as extra fingers.
So, this individual right here has polydactyly.
So if you count, they actually have six fingers.
This actually something that does come up.
This is a mutation that does crop up periodically.
It's a little harsh to refer to the person as a mutant because they have this.
It is a mutation which arises.
Now honestly, there's a little bit of truth to all those definitions.
Though less so for obviously the X-Men version.
[LAUGH] But again, the ultimate source of all variation is mutation.
It is any sort of change in the genetic code, okay.
So you can think of it this way, that mutations happen and they happen a lot.
They happen far more frequently than you may guess,
and you'll see in a subsequent video, we'll talk about mutation rates.
Now one of the most common types that we'll focus on for this, is an error
replication or a meiosis that leads to a change in a base or a nucleotide.
So imagine you have this stretch of sequence in a mom, okay?
And let's say the mom is homozygous with this.
So she has two copies of this stretch of sequence that starts with ATG.
Now let's say, in one of her eggs that makes the kid, there was this base change,
going from A to G.
So this is actually what's in the kid.
The kid then has a mutation.
He or she has a nucleotide variant that was not found in either of the parents.
So that is by definition a mutation.
Now importantly, let me emphasize what a mutation is not.