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Cell Biology

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4. DNA, Chromosomes, and Genomes

Genomic Comparison


Genomic Comparison

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Hi in this video, we're gonna be talking about genomic comparisons. So by comparing genomic sequences of different organisms, we can really provide insight into evolutionary changes that have led to the creation of life present on earth today. And so um we do this by just comparing the genomic sequences. So what are we looking for when we compare genomic sequences? Well, the genomic sequence of two species differ by the length of time they have separately evolved. So the longer there has been since two species evolved from a similar ancestor, no more changes that are gonna be. And so um when knowing this we can sort of assign some stretches of D. N. A different terms based on, you know, how different they are. So one of these things is purifying selection. And so what this is is that organisms with mutations that affect genes are really important genes die. So those mutations never accumulate. And so these genes can actually look very similar between very distantly evolved organisms because anytime there was a mutation in those jeans they died. And so these sequences are called conserved sequences. Because because they're so common between these really different organisms, they must have some form of critical function. This is actually about 5% of genes. And so um we think of conserved sequences generally in terms of regions of a gene or an entire gene itself. But this can actually happen um really on an entire chromosome or on chromosome segments. So we turn this as Sydney which is actually stretches of genes that the order of them is conserved on chromosomes between distant organisms. So what this means is if you were to have gene one gene to gene three gene for gene five, well that would remain that in that particular order um in very different organisms because that order is really important um for function. So that's really how some we just sort of an overview of how we begin looking at the evolution of genomic sequences and how we can compare them. And we start comparing them by looking at conserved sequences. And so um there's this idea I think that a lot of people have that genomic size is really important. Um And of course it is because it reflects the rights of D. N. A. Edition or loss. And when you're studying the genomic evolution of course you want to know what are the rates of D. N. A. Edition? What are the rates of DNA loss? But what it doesn't tell you. And what I think people really think it tells you is that a large a larger genomic size means that the organism has a larger number of genes and is more complex. But that's not true because it doesn't provide information on that. You can have a really simple organisms with a lot of jeans and a big genome and you can have really small genomes with fairly complex organisms. So genomic size does provide us information when we're comparing organisms but it's not a be all end all. It doesn't say okay well the largest genome is the most complex organism because it's not true. And so um how we do this which we've already talked about this term is philo genetic tree. Um And these are constructed using DNA sequences which trace relationships between organisms. Um Generally when we're looking at overall genome and comparing for philo genetic trees we can see more of that changes in n tron occur more rapidly and slower. Change concern occur and conserved genes with critical functions. Which makes sense because introns we don't need. So they're free to mutate as much as they want. Whereas genes that we really rely on for life can't change as much because we rely on them for life. So I remember back out of the way for a second and let's compare. I don't know if I can fit the title here. The title is comparing the genome size of various organisms. But let's just look at this graph. So down here on the X axis, you have base pairs. It's also here this is the number of base pairs obviously increasing. So there's larger genomes over here and smaller genomes over here and these are different organisms. And you can see that you know, bacteria and things that are generally smaller algae, they do have a smaller amount a smaller genome size. You know there's there's here it varies but when you start moving moving down moving across this way you can see that this doesn't necessarily hold true and the fact that here are mammals. So this includes humans here. And you can see that that's our size of the genome. But you also have flowering plants which have a huge range and goes much higher and much larger genomes than humans have or other mammals have. Now, flowering plants aren't necessarily more complex than humans, they're they're more simple. Um and a lot of ways, but they have or can have much larger genomic sizes than other organisms. So I think this is really important when comparing genomes between organisms to understand that genomic size doesn't equal um genomic complexity. So now let's move on.

Stretches of chromosomes where the gene order is conserved among different species is called what?


True or False:The larger the genomic DNA sequence is, the more complex the organism is.