PROFESSOR: Hello, and welcome to a help session on
complementation.
Today, we are going to be working
out a problem together.
If you have not yet had a chance to work out the problem
on your own, please do so now, and then return to this video.
All right, now that you've had a chance to look at the
problem your on, let's work it out together.
So, here we have a series of different fruit flies.
They all have these recessive mini-fly phenotypes.
So, we've noticed that there are lots
of different mutations.
And, now, we would like to put them into
complementation groups.
So, we start off by looking at this nice, large Punnett
square we have, where all the flies have been crossed to
each other.
So, if we look at A and B for instance, when these two flies
are crossed together, they still
have a mini-fly phenotype.
This means that the mutation is in the same gene and that
these two mutants do not complement each other, but
they make up one complementation group.
So if we look farther down this column, A and F together
also have a mini-fly phenotype.
This means A, B, and F, all three of these are in the same
complementation group.
So, now that we've already looked at A and B, let's
continue on to C. So, C has a normal fly in all of these
instances except this one.
When C and E are crossed together, they also have a
mini-fly phenotype.
Thus, C and E also form a complementation group.
So, now we're done with A,B, C, E, and F. So looking at D,
D when crossed to all the other flies, you never get a
mini-fly phenotype.
So, D must be in its own complementation group.
Great, so we've identified all three complementation groups.
So, moving on to the next part of the problem.
We are asked, are mutations B and C in the same gene, or are
they in different genes?
All right, so, if we look over here at B and C together, when
these are crossed, we get a normal fly.
This means that the mutations were able to
complement each other.
Meaning that the two mutations occur in different genes, and,
thus, when you cross the flies, they're able to
compensate for each other.
So, they're in different genes.
All right, now, in the last part of the problem, we're
told that we are introduced to a new fly, or a new mutant
fly, G. When G is crossed to A, we get a
mini-fly phenotype out.
Also, when we cross G to B, we also get a mini-fly phenotype.
So the question is, what does this suggest to us
about mutant G?
Looking over here, we notice that A and B are in the same
complementation group.
When A and B are crossed together, we also get
mini-flies So, this suggests to us that G is yet another
member of this complementation group.
Thus, G also falls into complementation
group number one.
This concludes our help problem on complementation.
Thank you for joining us.