Today we talked about:
- the differences between retrotransposons and 'regular transposons'
- the two main components of a 'regular' transposable element (not a retrotransposon), and what happens if one of them is mutated
- hybrid dysgenesis in flies (P elements).
- predicting the outcomes of crosses where one or both parents carry one or more transposable elements;
- diagnosing the presence of a transposable element in a gene.
If you have any questions regarding these topics, please post them here!
If you have questions regarding how to clone a gene taking advantage of a P element, you can also post it here, but please start the comment with "Cloning and P elements question".
Have a good weekend!
Pam
PS: more about P elements here.
13 comments:
Hi Pam,
for question 10 of chapter 14,
do we have to consider maternal effect, that is can we say that the female drosophila has repressor in her eggs and the resaon why there are variable proportions of singed progeny is that despite the presence of repressor, the P element is still able to jump out and so we are able to observe a relatively high frequency of revertance from singed to wildtype at ~ 1/1000.
Thanks.
Hi Pam,
i have a similar question; why is that they are numerous patches of sn+ in the female drosophila before mating, could it be that the female has no repressor and therefore, when mated with sn males the p element from male is able to jump around, leading to hybrid dysgenesis?
Thanks.
Hi Pam,
Just a general question. Human genomic DNA has a lot of spacer DNA and that can allow transposition to happen without causing harm to the cell... but wouldn't transposition change the reading frame and affect the gene sequences thereafter?
Thanks for the clarification.
HI Pam,
can you explain slides 22 and 36 from Tom G's Transposable elements lecture?
Thanks.
hi, Pam,
Can you explain how enhancer and promoter trap work?
P element inserted into a gene causes mutated phenotype. We isolate these mutants and used these mutated gene as probe to find wild type gene. But how do we isolate those mutated gene in the first place? Do we do a genomic library of those mutant?
Thank you very much
ABOUT TRANSPOSONS
You asked a lot of questions related to transposable elements….
• question 10 in chapter 14 (the singed flies) :
Our explanation was that the mother that has the patchy phenotype will make repressor and deposit it into her eggs (that is, if the transposon in question is a P element). So, in her offspring, P elements that are present in the genome won’t move anymore. However, while she was still an embryo, she had no repressor, because her mother did not make any. So, in some of her cells the transposable element ‘jumped out’ of the singed gene, causing a reversion to the WT phenotype. Some of these cells went on to become eggs. So, she has 2 kinds of eggs : with or without the transposable element.
When she mates (note that the male does NOT have a P element!), it’s really just her eggs that come in contact with the male’s DNA. The transposable element in her eggs (in the eggs that still have it) does not move, because she has deposited repressor in the eggs.
Cheers
What you describe isn't really an enhancer or promoter trap. Don't worry, we'll go over how to clone a gene based on its phenotype and with the use of P elements on Monday. In the meantime, I'll post some summary notes on the 'other page'.
I'll also try to put together something for Tom G's slides 22 and 36.
It's great to see that you are working hard on this!
Cheers
Pam
Hi Pam,
so how is the 1/1000 mutation rate
linked to P element mobilization?
Is it true that even in the presence of repressor, the P element is still able to move?
Thanks.
1/1000 reversion rate that Craig was talking about is the result of the fact that about 1/1000 times, the transposon will jump out of the gene it is in (if it is in a gene) and do so precisely, without leaving a piece behind and without picking up an additional piece.
If you have repressor, the P does not move.
Cheers!
TOM G'S SLIDE #22 ON TRASNPOSABLE ELEMENTS:
Remember that we said that the dysgenic F1 flies (that is flies that have hybrid dysgenesis) have reduced fertility and their (limited) offspring show lots of mutations? This slide just shows how we can determine the mutation rate of a certain strain of flies (or even, of a given fly!).
It's mainly for your own interest/curiosity.
ABOUT SLIDE 36 (gene tagging): we'll talk about it on Monday...I may refer to it as "P hopping".
Cheers
Pam
in dna in situ hybridizatiom, do we know there is a deletion if our probe don't bind to any of our chromosome? What about inversion?
Nice question!
if our probe is for a particular region of the genome, but it does not hybridize to anything, then yes, we probably have a deletion. If it's an inversion, then the probe would hybridize to an unusual spot (where the sequence of interest now is)
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