In Bacillus subtilis, linkage analysis of two mutant genes affecting the synthesis of two amino acids, tryptophan (trp₂⁻) and tyrosine (trp₁⁻), was performed using transformation. Examine the following data and draw all possible conclusions regarding linkage. What is the purpose of Part B of the experiment? [Reference: E. Nester, M. Schafer, and J. Lederberg (1963).]

Question

In Bacillus subtilis, linkage analysis of two mutant genes affecting the synthesis of two amino acids, tryptophan (trp₂⁻) and tyrosine (trp₁⁻), was performed using transformation. Examine the following data and draw all possible conclusions regarding linkage. What is the purpose of Part B of the experiment? [Reference: E. Nester, M. Schafer, and J. Lederberg (1963).]

Table showing donor DNA, recipient cell genotypes, transformants, and their counts for bacterial gene linkage analysis.

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together D N A from a bacillus septal A strain with genotype TRP plus T Y R plus was transformed into another bacillus septal. A strain with genotype trp minus T Y R minus. So this is what is happening. You have your bacterial D N A, it's got the genotype TRP minus T Y R minus introduced to it transformed into it is another bacterial fragment DNA fragment with T R P plus T Y R plus. And what happens is crossing over. And so you get different combinations of the genome types. And so our question states that the transform ints or the different combinations obtained whereas follows TRP minus T Y R plus equals 100 T R P plus T Y R minus equals 125 and TRP plus T yr plus equals 175 determine the incorrect conclusion in relation to this experiment. So we want to know which of these are not true. And so we have a, the frequency of co transformation is 43.75. Well, what is code transformation? Well, that's when two or more genes are transformed together. And there's an equation for this and it says follows. And so the frequency of co transformation is the number of co transform ints over the total number of transform intense. Well, what are the co transform incense? And in our case, it's the TRP plus T Y R plus because they're the genotype that appear together in the original bacterials dreams. And so our total number of co transform into is going to be 100 and 75 over the total number of transform ints is going to be 100 plus 100 and 25 plus 75. And that's gonna give us 1 75 over 400 if we multiply that by 100 that gives us 43.75%. And so A is correct. And so we'll eliminate it because it is true. Now, let's look at B the high percentage indicates successful co transformation. So as successful co transformation occurs, the total number of co transform ints would go up and as that number went up, this would also increase the overall percentage or frequency of co transformation. And so B is correct as well. And so we will eliminate B. Now, let's look at D, the T R P and T Y R genes are possibly located together on the same chromosome fragment. Now recall that genes can only be co transformed when they are within the same vicinity on the same chromosome. And so D is also true. Lastly, let's look at see the jeans T R P and T Y are, are not linked. And again, this is the incorrect statement because when genes are in close proximity to each other on the same chromosome or fragment, it indicates that the genes are linked. And so c is the correct answer. Alright, everyone, I hope you found this helpful and I'll see you for the next practice problem.

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Key Concepts

Linkage Analysis

Transformation

Amino Acid Synthesis