XIST

And to just ask, is a big piece of DNA with this gene sufficient if I put it somewhere else in the genome to switch off a chromosome? And for the first few years, I would do this experiment with bigger and bigger pieces of DNA.

And even the biggest piece of DNA with Xist would not be sufficient.

We knew that this gene Xist was actually necessary because if you deleted it or took it away, the chromosome couldn't get switched off.

And yet, if you just took it as a single copy and put it somewhere else, it wasn't working.

So it was a bit of an enigma.

That's right.

We know that genes, particularly in organisms like mammals, have to have nearby sequences, other bits of DNA, to make sure they get switched on and off in the right place at the right time.

So my quest was to understand what are the missing bits of DNA that will allow Xist to be switched on only when there are two X chromosomes in a cell and only on one of the two X chromosomes.

So they are part of a protein, and then they will bind to DNA, and this way the protein knows where to go.

And then there's, of course, we'd already talked about this, um, the X inactivation, and there is also a long non-coding RNA called Xist involved in this process, which will help in X inactivation.

I wanted to just mention that RNA is similar but not the same to DNA.

Um, in-- mostly it is present in single-stranded in the cell, not double-stranded.