Cytological Maps

00:00 When we have labelling and tags, we might get something like these cytological maps. This is a cytological map of one chromosome. It doesn't really matter what it is, but that chromosome has been broken down into sections and we can know the physical locations of genes on the chromosomes. This is like our country wide map. We are looking at the states. We can see Denver in there somewhere. We have these landmarks. We know we are going to pass through some other states before we actually make our way to Denver, but eventually will get Denver. Cytological maps use staining in order to mark places on the genome. But if we want to know specifically where a gene is, then we need to get a little bit more granular. Some examples of how we might use these techniques in analysis of mutations or such analysis of disease are using FISH hybridization. This is one of the staining techniques we could use. FISH means fluorescence in situ hybridization and it is used to mark chromosomes with fluorescent dye and see if they have these particular genes. Here is an example. We will look at chronic myelogenous leukemia, which is a condition that results from a translocation on chromosome 9 and 22. It is a reciprocal translocation.

01:30 Each chromosome swaps pieces during the process of meiosis and thus will form a gamete that has a translocated chromosome. It is a chromosomal level mutation.

01:46 Here you can see on the right, we have our translocated chromosome with two pieces. It is much smaller, but what you noticed is it has both the green dye and the red fluorescent dye on it. When we visualize this, we can see that in this visualization, you see both the red alone and you see green alone, but you also will notice that there is a green and red marker. The green is very close to the red that is showing that this individual does indeed have this reciprocal translocation between chromosome 9 and chromosome 22 for one of their chromosomes. They still have the two separate pieces marking 9 and 22 and then they have an additional one, which is the translocated piece. One copy has become translocated and the other copy is normal. This person does indeed have the chronic myelogenous leukemia and what happens there is we have an over-production of a protein kinase that ends up producing red blood cells at a much higher rate that needs to happen. Not a great situation, but this is an example of how we might use a cytological map to see where particular mutations are on chromosomes or if an individual has that particular mutation.