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Office hours today: 12:30-1:30, 301 Barker,
Becky’s Wed 11-12pm section will be in 110
There will be lecture Friday and next
Monday, it’ll be a summarizing lecture. Then
I’ll schedule a review session next weekend
before the final but I don’t have a room yet so
I’ll get that info to you soon.
Last Monday, we left off at how you can use
genetics to understand multi-cellular
It’s using the same things that
we’ve talked about that you already know –
altering the cell cycle (lengthening or
shortening it), using signal transduction
pathways to send messages from one end of the
organism to the other, and finally, utilizing how
to activate and repress transcription and
translation. So it’s just using things we’ve
already studied and applying them to looking at
how a multi-cellular organism develops.
As you know from the beginning of Chapter
20, there are several organisms that people
doing genetics prefer to use. Those are
Drosophila, worms, zebrafish, plants
(Arabidopsis), mice, and yeast is also useful.
The reason those organisms are used is because
you can do genetics and make mutants that you
want to make to ask questions in a way that you
couldn’t do with humans. So even though it
seems pretty bizarre to think about how
Arabidopsis, for example, can give information
about human development, all of these
organisms can tell us about mammalian
development because so much is conserved
the genome from humans down to yeast.
The question where we left it last time was
‘how do you know what cells or tissues are
affected by the absence of some gene
function?’ It’s not always obvious. It’s not the
case that if you knock out a gene in this tissue,
I’ll see an effect in this tissue. For instance, the
pituitary gland has effects on other organs so a
mutant in a pituitary gene may not affect the
gland at all but the target organ. So in this
figure, let’s consider tissue differentiation in
Arabidopsis. Here’s a picture of the apical
meristem. So these stems will differentiate into
flower cells; this is a cross-section.
There are three types of cells: L1, L2, L3.
There’s a gene called Agamous+ whose wt
activity is necessary for L1 cells to differentiate
into flower cells. So mutation in Agamous+
will result in lack of flower cells. It turns out
when you do the experiment and look at where
the Agamous gene function is necessary, it’s
not necessary in L1 cells but in L2 cells.
Geneticists determined those using mosaic