In order to get insights into the pathway of synthesis of the fatty acid FT, with 18 carbons and one unsaturation, you develop the following forward genetic screen: you know wild type yeast can grow in media lacking FT, and you use a yeast knock out library in which each of the yeast clones to be analyzed has one gene deleted. You then look for clones that grow slowly in media lacking FT, and you proceed to isolate and identify the genes absent in each of these clones.

A) What can you say in terms of necessity and/or sufficiency about the genes isolated using this approach? Justify your answer.

Max 3 sentences

B) Considering the phenotype studied in this screen, what could be the role of the isolated genes in terms of FT? Justify your answer.

Max 3 sentences

You focus your attention on three of the genes isolated: SFT1, SFT2 and SFT3. The KO yeast of SFT1 is non-viable in the absence of FT. KO strains for SFT2 and SFT3 grow slower in the absence of FT, and when the double KO (SFT2 and SFT3) is tested, the cells are non-viable in the absence of FT.

To try to establish the cause behind the cells dying, you observe the morphology of the SFT1 KO and the double mutant SFT2 and SFT3 cells before they die. Some of the images you obtained are displayed below. A: wildtype yeast, B: double KO SFT2 and SFT3. Please notice that SFT1 KO images are not displayed, but they are similar to the double KO mutant with more severe defects. Looking at the images, you can appreciate some differences, but you are not sure about them, so you talk with an expert colleague who tells you: “the double mutant clearly has a wider intermembrane space between the inner and outer nuclear membrane”.

C) Based on the images displayed and this statement, are these images taken with an electron or a light microscope? Justify your answer.

Max 3 sentences