BIO156 online / summer – Chapter 13 (part B): chromosomal mutations

BIO156 online / summer – Chapter 13 (part B): chromosomal mutations


Hi! Let’s look at some chromosomal mutations. And, I want to start by saying that in humans
we do not see many full mutations where an entire chromosome is either missing or added
extra. The few that we have already earlier talked
include Down syndrome (that was the extra chromosome 21), Turner syndrome (which was
only one X), and Kleinefelter syndrome (which was XXY). What is more likely is that we have changes
in the chromosome structure. And, these can either be that something breaks
and re-unites, or there can be one of these other events. And, we will go these other events through
next. Actually, there are a few others than what
your textbook mentions. And, let’s go these through using this as
an example. So, what we have here is a chromosome called
‘beast.’ And, we will look at a few cases where something
goes ‘off’ with the coding sequence of this chromosome. So, in a deletion some part of the chromosome
is lost, from the middle, and the ends of what is left join together. And, as we see here, the entire meaning of
the chromosome may change! Some common examples of this include Williams
syndrome and this ‘cat’s cry’ syndrome. We have discussed these in more detail earlier,
you can review them from Chapter 9. The next one that we have to look at is duplication. And, in duplication a segment of of chromosome
is repeated, like in this example the part ‘EA,’ which makes it sound like it is
a girl called Bea that is from the East. Or, I do not know what it makes it say, but
it has a duplicate of one segment. Here we have an inversion, which is basically
that a segment of a chromosome is flipped 180 degrees. So, in reverse. And, again, that would change the ‘meaning’
of this chromosome, wouldn’t it? Usually, really, this is not a huge issue,
though. What else can I think of? Well, there can be a translocation, in which
segments between two non-similar chromosomes are changed. Normally, this would simply result still to
the same amount of protein being made, and all being well. This is, unless that breaking off a segment
happens in the middle of a gene. So, in this example, just the order in which
these are presented changes. Both proteins are still made. Like I said, there are many other possible
mutations, your textbook has just picked some that it focuses on. There are even some where two of these act
at a same time, like here a combination of a duplication and inversion. It can get pretty complicated, huh? I think that we will finish here, and look
at some methods to test for genetic mutations in the next section.

Leave a Reply

Your email address will not be published. Required fields are marked *