101/162.101 MAN/ALB Internal only QUESTION 14 NSB/ASR Sc A PhD student analysed
ID: 276093 • Letter: 1
Question
101/162.101 MAN/ALB Internal only QUESTION 14 NSB/ASR Sc A PhD student analysed the expression pattern of a developmental gene, devA in the fruit fly Drosophila melanogaster, using reverse-transcription (RT)-PCR He did a multiplex PCR in which primers for a constitutively express gene (tubA) were included along with devA primers. The experiment yielded PCR products as shown in the gel diagram below a) Developmental stage larval larval larval pupa adult tubA devA direction of DNA movement in gel ) Explain why RT-PCR (and not just PCR) was used to study the gene (2 marks) expression () Is the tubA or devA PCR product larger in size? How can you tell? (2 marks) (i) Does the size of the PCR product tell you anything about the expression of 2 marks) these genes? Why or why not? iv)From these results what can you conclude about the expression of devA and 2 marks) why? A had shown the same expression pattern as devA what would you (2 marks) conclude from this experiment? Page 15 of 16Explanation / Answer
Answer:-
i) For checking a gene expression pattern of a gene one has to check the mRNA expression pattern of that gene and that is why RT-PCR was used instead of normal PCR. Reverse transcription PCR allows the cloning of expressed genes (mRNA) by reverse transcribing the mRNA of interest into its DNA complement through the use of reverse transcriptase enzyme.
ii) tubA is larger in size as it is placed above in the gel opposite to the direction of DNA movement in the gel. A higher size DNA will be at the top as it will not be able to cross the polymerized holes in the gel easily and thus cannot travel faster and the gene lower that size will run faster through the gel and thus be below the larger size DNA.
iii) No the size of PCR product doesn't tell us anything about its expression. It may be a large size DNA or a low sized DNA it doesn't matter. The size of the band on the gel however, tells us about the expression pattern. The thicker and brighter the band is the more expression of the protein has occurred.
iv) Dev A expression decreases as the stages progress. As can be seen the picture its expression was strongest in the 1st larval stage and gradually it decreases and we can see no expression in the adult stage.
v) If tubA had shown same expression pattern as devA then it would have meant that the experiment was not performed correctly as tub A is a housekeeping gene (control gene) and it is expressed at all times in equal concentration at all the stages, so its expression should be equal in all the stages. That is why these housekeeping genes are used as a control.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.