An attribute of growth behavior of eight bacteriophage mutants...

Question

An attribute of growth behavior of eight bacteriophage mutants (1 to 8) is investigated in experiments that establish coinfection by pairs of mutants. The experiments determine whether the mutants complement one another (+) or fail to complement (-). These eight mutants are known to result from point mutation. The results of the complementation tests are shown below.

Identify the mutants of each gene.

Table showing complementation results of eight bacteriophage mutants in genetics experiments.

In each coinfection identified as a failure to complement (−) in the table, researchers see evidence of recombination producing wild-type growth. How do the researchers distinguish between wild-type growth resulting from complementation and wild-type growth that is due to recombination?

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next problem. It says a group of four F root fly mutants X Y Z and W was studied for their wing development. The mutants are known to result from point mutations. The following table shows the results of the complementation test between the mutants. We have our table showing crosses between all of the different mutant strains and whether they compliment or don't complement each other with a minus sign showing they do not complement each other and therefore, still show the mutant phenotype in the offspring and A P plus sign showing they do not that they do complement each other. And therefore the wild type phenotype is reestablished in the offspring. In the experiment. Researchers observed wild type growth resulting from recombination and coinfections identified as failures to complement minus in the table. How do the researchers distinguish between wild type growth resulting from complementation and wild type growth due to recombination? So we'll go through our answer choices and read them. But before we do go through them and evaluate them, I just want to have us recall and kind of understand what's going on here. So again, usually, this complementation test would show us how we would would establish whether they complement each other or not. Is the phenotype of the offspring wild type phenotype means that the two mutations are in different genes because the mutations are generally recessive, they need to be present in two copies to show that mutant phenotype. The complementary situation results in a hater as I get for two different mutations who therefore shows the wild type being a type when it's non complementary. So we know that the mutations are in the same gene, we essentially have a homozygous recessive offspring. And therefore the mutant phenotype since they have two mutated copies of the same gene. However, these mutations don't need to be in exactly the same place. And we know from our question that they're only point mutations. So they could be a single base pair mutation in a slightly different place that impairs the functionality of the same gene. So this is saying that sometimes recombination occurs between our two copies. And if recombination occurred in the right place, you could swap out those pieces and end up with a functional allele that then because our our mut mutant has to be re homozygous recessive to show the phenotype. If you manage to correct one of those allies through recombination, you would show wild type phenotype. So that's what the situation is happening here. And it's saying, how would scientists know whether these wild type offspring they're looking at are wild type because the genes were complementary or wild type because recombination occurred in something that was originally non complementary as determined by earlier complementation tests. So with that in mind, let's go through our answer choices. Joyce A says they perform additional complementation tests between the same mutants to confirm the result. Well, this is not going to be helpful because we already know the genes are not complementary. So that would just keep telling us the genes are non complementary. So that is not the answer we're looking for. Then choice B says they sequence the genomes of the mutant and wild type fruit flies to identify any genetic changes. And this will be our answer because if our wild type phenotype is due to complementary genes or complementary mutations, then there's no change to the gene to the mutant gene. Uh that they're just, they're just heterozygous. That's all. However, if recombination has occurred, you would see a change in the genetic sequence of that mutant strain. So that would distinguish between those situations. Choi C says they compare the wing morphology of the recombinant and complimented fruit flies. Well, this would not be our answer because again, we've already established that the mu mutants show the same phenotype. That's why we're trying to figure out if they're on the same gene or different genes because they lead to the same phenotype. So that wouldn't be our answer. And then finally, choice D says they use a different set of mutants that are known to complement each other to compare the wing development. Well, again, we've already established whether they complement each other or not, all of the mutations show the same effect on the phenotype of the wing. So comparing wing development with different mutants won't help us here. So not our answer choice. So again, how do the researchers distinguish between wild type growth resulting from complementation and wild type growth due to recombination choice? B? They sequence the genomes of the mutant and wild type fruit flies to identify any genetic changes. See you in the next video.

Key Concepts

Complementation

Recombination

Point Mutation

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