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5. Genetics of Bacteria and Viruses





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Hi in this video I'm gonna be talking to you about transaction. So transaction is the process of using a bacterial fage to transfer foreign D. N. A. Into a bacterium. So this was discovered in 1951 by Leader Bergen's Ender. So what they did is they had to mutant E. Coli strains. So these are two mutant bacterial strains that they mixed together. And when they plated them thinking that they plated them on conditions where neither would grow. So they have sharing a ensuring B. And they played and they mix them and they plated them onto a plate where they shouldn't grow no growth. So that's what they were expecting. They were thinking they were going to die. But essentially what happened is that some of them survived about one in every 10 to the fifth E coli cells did grow meaning that some kind of DNA transfer had to be occurring. And so what they thought they were like okay well conjugation. We just figured this out. So it's likely conjugation. And so what they did is to prove this is they put a filter in the in the growing area. And so what the filter did is it would stop conjugation. It was so small that the sex pill i that you know connect the two bacterial cells together couldn't form. So they completely inhibited conjugation. And they did the experiment again. But what they saw is that the cells still grew and they were like okay well this is definitely not conjugation. But what's going on? Well they looked at the filter and they said well the only thing that could fit through this filter is a bacterial fage. And so they knew that some kind of virus had to be transferring DNA between the two cells to allow them to survive in this area where they shouldn't be able to survive. So here they are. They played it to bacteria played where neither should grow. But they both both grew meaning that some kind of DNA transfer had to happen here. And they use the filter to not only prove it wasn't conjugation but also to say okay that only a virus is this small to fit through this filter. So it has to be that that allows for this type of uh DNA transfer. So there are two main types of transaction. The first is generalized meaning that they can transfer any part of a bacterial chromosome. They can transfer any kind of bacterial DNA. So usually what happens is that some type of bacteria has been list usually by a virus, right? Um and that releases some cut up D. N. A. In the environment. The bacteriophage will take it up and then transfer into another cell during the infection process. So this is generalized transaction. It's just started taking up whatever has been life and put into the environment. There's a different form called specialized transaction. And this is the ability to transfer only specific parts of a bacterial chromosome. So how this works is there's a a molecule called a transducer. And this transducer actually inserts itself only in one place in the bacterial chromosome. So it has a very specific sequence. And it says when that virus is in there it's going to you know put itself right in that sequence when that bacteria is um and that transducer is stimulated to leave either by a chemical or a virus or you know it can be stimulated in lots of different ways but something activates it to leave. It picks up the nearby genes. So it's only taking those genes in that one specific sequence that are nearby where that transducer inserted itself into the cell. That then goes into the page and then can be transducer into other bacterial cells. So here's generalized transaction. You have chopped up D. N. A. Here part of it gets into a fade and that goes into a bacteria specialized transaction is different here. You have a fade with a transducer. The transducer upon infection gets into the bacteria, it inserts itself in this one area here and that will then go into other pages and be transferred into bacteria. So this is always going to be the same sort of genes that are transferred here. And this can be any kind of sequence. It doesn't even have to be a gene. It's just any kind of broken up sequence now generalized transaction. This part that kind of takes up anything can also be used to map genes and study gene linkage. Because the closer the two genes are the more likely it's going to be that their transducer together. And this is called co transaction. When a single bacteriophage carries more than one gene in it. Now. Before when we've been using mapping, we've been using recombination frequencies looking at either the offspring themselves or the bacteria in case of bacteria of age recombination frequencies. But in this case we call this the co transaction frequencies. And and it measures how often two genes are co transducer. The closer to genes are the more likely they're going to be co transducer together. And the farther they are the less likely. So you can use this co transaction frequency to measure how close the genes are together. So here we have an example chop D. N. A. You can see here that the genes are close together and hear that they're farther apart. And that means when the D. N. A. Was chopped these two stayed together and these two were chopped up. And so when these are getting to the faith and our transducer into the bacteria then you can see that these two stay together. And this is called co transaction. Now the frequency of co transaction can be measured in a lot of different experimental ways. But essentially that co transaction frequency allows you to be able to identify how close the genes are together and how far apart they are. So that's transaction. And with that let's now move on

True or False:Transduction uses viruses to transfer foreign DNA into bacteria


Specialized transduction differs from generalized transduction because specialized transduction is defined by what?


A cotransduction experiment was performed with two bacteria strains. The first train has the genotype l+ g m+ while the second strain has the genotype of l g+ m. The researchers found that 46 colonies had cotransduced m+ with l+, while only 25 colonies had cotransduced g with l+. Using this information determine which of the following gene pairs are closest together.