This section of MCB2020F covers the following three topics - Eukaryotic genome organisation, Extra-nuclear inheritance and Evolutionary genetics.
In Eukaryotic genome organisation we will cover how DNA is compacted into chromosomes and how this affects gene function. We will examine chromosomal ...
extra nuclear inheritance and evolutionary genetics
lecture notes
Written for
University of Cape Town (UCT)
MCB2020F
All documents for this subject (21)
Seller
Follow
laylaalexander
Content preview
🥌
L3 - Chromosomal
Rearrangements l - Deletions,
Duplications & Inversions
Chromosomal Rearrangements and Changes in
Chromosome Number
In this section we are going to talk about chromosomal rearrangements and
changes in chromosome numbers.
We noticed when we spoke about karyotyping how all placental mammals had
the same DNA content, yet they had different chromosome numbers.
So chromosomes have clearly been rearranged in terms of their order, with
respect to which chromatin is in the same neighbourhood with which other bits of
chromatin.
And we also had chromosomes being broken and therefore more chromosome
numbers in some species versus less chromosome numbers in other species.
These chromosomal rearrangements and changes in chromosome number have
reshaped genomes over evolutionary time.
For example, if we looked at mice and humans, we have this interesting
evolutionary paradox where mice and humans have very, very different
karyotype numbers.
They have different chromosomal patterns, and they have different numbers of
chromosomes. They’re clearly two very different species.
However, if you looked at a certain genetic block on any chromosome in human,
and you looked at the sequences neighbouring that genetic region, if one were
to find the same genetic sequence for the mouse and looked at its neighbouring
sequences, you’d find very close genetic similarity over thousands and
thousands of base pairs.
And these similar blocks are called syntenic blocks, or blocks of synteny.
, So one has great synteny between mouse and human chromosomes, yet the
chromosome number and the banding pattern is different.
So, how do we explain this? In fact, people have thought about it in another way.
One could reconstruct the mouse genome by taking the human genome and
breaking it in about 350 fragments, each of about 16 megabases, and just paste
it into a different order.
So you’ve got the same genetic kind of foundation, it’s just built in a different
way.
So in a sense, you can almost think of these synteny blocks as blocks of Lego,
and you’re building a structure. So the structure one builds as a mouse I clearly
mouse-like, but the blocks are the same. So on this picture on the far right of the
slide we can see mouse chromosome one, and it has a particular sequence. And
the sequence of mouse chromosome one, you can find in giant blocks of
synteny across human chromosomes. So, for example, on the human
chromosome, for the mouse you’ve got what would be chromosome eight, a bit
of chromosome six, a bit of chromosome two, some chromosome five, a bit of
chromosome 18, more chromosome two, and then finally chromosome one is on
the mouse chromosome one. And this is indicative of the chromosomal
rearrangement that’s occurred over evolutionary time, and defines the species.
Different Types of Chromosomal Rearrangements
So we’re going to talk about a range of different chromosomal rearrangements.
Deletion: Removal of a segment of DNA
The first kind of chromosomal rearrangement we’ll talk about is where you delete
a bit of DNA material, a bit of chromatin.
So if you look at the picture, there is a chromosome that has eight chromosomal
regions.
Now, be clear that each number does not represent a gene. It’s a giant
chromosomal region. Remember, chromosomes have megabases of DNA.
So each block represents a large chromosomal region. So the picture has eight
chromosomal regions, and then note chromosomal region number four is
deleted in the part of the diagram on the righthand side.
So clearly, there’s a deletion and you’ve lost genetic material.
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller laylaalexander. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $6.01. You're not tied to anything after your purchase.
