A wild-type culture of haploid yeast is exposed to ethyl methanes...

Question

A wild-type culture of haploid yeast is exposed to ethyl methanesulfonate (EMS). Yeast cells are plated on a complete medium, and 6 colonies (colonies numbered 1 to 6) are transferred to a new complete medium plate for further study. Four replica plates are made from the complete medium plate to plates containing minimal medium or minimal medium plus one amino acid4 (replica plates numbered 1 to 4) with the following results:

Identify any colonies that are his⁻, arg⁻, leu⁻.

Accepted Answer

Hi, everybody. Let's look at our next question. The oxo trophic selection method is a genetic research technique used to select and isolate cells with a specific genetic mutation by growing mutant cells on a medium that lacks an essential nutrient that the mutant cells cannot produce. Can you identify the colonies that are his minus arginine minus and lucine minus using this method. So we'll walk our way through the answer choices talking through each one in just a moment. But first, let's just briefly consider this question and what it means. So we're talking about selecting colonies for mutation when the mutation causes the cells to be unable to synthesize. So mutation to be unable to synthesize a specific essential nutrient. So if the cells are grown in a medium that lacks this nutrient, they will not grow, they need to get it from the medium. So our question asked us, can we identify colonies that have mutations that have caused them to be unable to synthesize histidine, his hiss arginine or lucine using this method. So let's look through our answer choices. Choice A says yes, because these colonies will not be able to grow on a minimal medium that lacks histidine arginine and lucine respectively. Well, right here, we have a correct answer. Going to circle choice a because a colony that is his minus. So has a mutation in its histadine synthesis pathway will not be able to grow on a medium without histine. Same with an arginine minus won't grow on a medium with lacking arginine, lucine minus won't grow on a medium lacking lucine. So that is the way to distinguish the colonies that have these mutations. So we have our correct answer already. But let's go through our other answer. Choices to be thorough choice. B says no, because these colonies will be able to grow on a middle and medium that lacks histidine arginine and lucine respectively. But this is not correct if the gene that controls the histamine pathway or arginine pathway or lucine pathway has been mutated. So the cell can no longer synthesize that particular essential nutrient. They would need to get it from the medium and wouldn't grow if it's lacking in the medium. Choi says no, because the presence of a mutation in any one of the three genes would still allow the colony to grow on a minimal medium that lacks histidine arginine and lucine. Well, again, if the medium lacks all three a presence in any one of the three genes or the presence of a mutation, excuse me, in any one of the three genes would mean that these cells could not grow if they're missing all three of those, because they will need the one that they're missing, that they have the mutation in the pathway. So choice C is incorrect and finally, choice D no, because the missing nutrients can be synthesized by other pathways in the mutant cells. And that is an incorrect answer because when that pathway is destroyed by mutation, there is no other way for the cell to synthesize them. So let's look again, we'd say, can we identify the colonies that are his minus a minus loose minus using this method? And our answer is choice. A yes because these colonies will not be able to grow on a minimal medium that lacks Histon arginine and lucine respectively. See you in the next video.

Key Concepts

Haploid Organisms

Mutagenesis and EMS

Amino Acid Auxotrophy

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