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Gene Activation

APBIO-3W1CVV

Fijalkowski, Artur Jan. Yeast Mating Scheme. N.p., n.d. Web. https://en.wikipedia.org/wiki/File:Yeast_mating_scheme.svg.

Haploid yeast comes in two varieties, a-type cells and $\alpha$-type cells. The a cells produce a mating pheromone known as a-factor and have a surface protein known as STE2. The $\alpha$ cells produce a mating pheromone known as $\alpha$-factor and have a surface protein known as STE3.

The yeast cells release their mating factors into the surrounding area, as shown in the image. These signal molecules can be received by the STE receptor proteins on the membrane of the opposite haploid cell type, causing the receiving cell to grow a mating projection, known as a shmoo, in the direction the cell signal was received from. STE2 can only respond to $\alpha$-factor, and STE3 can only respond to a-factor, ensuring that the yeast mates with cells of the opposite type.

Transcription of the genes for STE2 and STE3 are controlled by the MAT gene, which serves as a transcription factor. The allele MATa activates transcription of the genes for STE2 and a-factor while simultaneously repressing transcription of STE3. The allele MAT$\alpha$ activates transcription of STE3 and $\alpha$-factor while simultaneously repressing transcription of STE2.

If a researcher tested for the presence of particular genes, which of the following would be TRUE of a-type cells?

A

The cell would carry the genes for STE2 and MATa but not the genes for STE3 or MAT$\alpha$.

B

The cell would carry the genes for STE3 and MATa but not the genes for STE2 or MAT$\alpha$.

C

The cell would carry the genes for STE3 and STE2 but not the genes for $\alpha$-factor or MAT$\alpha$.

D

The cell would carry the genes for STE3, STE2, and $\alpha$-factor but not the genes for MAT$\alpha$.