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Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Karyotypes are images which depict individual chromosomes. Karyotes are used by scientists to study chromosomal regulation and evolutionary events in living things. Scientists are able to study the number and appearance of the chromosomes. Through karyotypes, it is often possible to see genetic disorders such as Down's Syndrome simply by looking at a karyotype.

In Biology there's something called a karyotype that is often used to help diagnose the issues with somebody's chromososmes.

What is a karyotype? Well, basically what they do is they get a cell from somebody and they let it undergo cell division and right as it's starting to do cell division and it's tightened up all of its chromosomes, they stop the cell from progressing and then they pull out those chromosomes and they take pictures of them and then somebody has to sit there and pair them up. Luckily nowadays, a lot of that is being done by computer but still it can be kind of hard. We take a quick look over here, you can kind of see how that looks. Here we see a nucleus and what they've done is they've used various stains in colors to help spot different parts of the different chromosomes. And now, this is what the chromosomes would look like. Somebody had to sit there and pair them up and arrange them. The yellow stains have stuck to chromosome number 1, the red number 2 and so and so forth.

The chromosomes here are arranged and named in order of their size. You can see that these two match each other. Again they're called homologous chromosomes. They carry similar traits. This one may be from mummy that one from daddy and both carrying your mum and dad's versions of say the gene that could determines whether or not you can roll your tongue or the shape of your earlobe.

Down here is the x chromosome and you can see this person has two x chromosomes which tells you, yeah. They're female. What would it look like if they were male? Well, you'd have the same pattern of the autosomes but down here, you can see that the x and y chromosome looks significantly different with the y chromosome being much much smaller than the x chromosome. It carries up far fewer genes.

Last, this gives you a view of another karyotype and everything looks the same. Down here they said this or that. Generally you don't get a choice, no little check off boxes. What's significant here you can see this person rather than having pairs of chromosome number 21. This person has three copies of it. That is called a trisomichromosome abnormality. So this is trisomi 21. You may have heard of this syndrome before. It's otherwise known as down syndrome. This is caused by problems during meiosis when the chromosomes, the homologous chromosomes are supposed to separate but unfortunately something goes wrong and they either stay together or one side doesn't get one. and that can cause major problems with the development of that child.