Question

After performing an additional experiment, you realize that yeast 4 actually doesn’t have gene in its genome, but yeast 5 and yeast 6 have it (yet they are not expressing it).

a) What experiment you could have performed in order to realize that yeast 4 doesn’t have gene in its genome, but yeast 5 and 6 do (even though they are not expressing it)?

b) What could be two different reasons why yeast 5 and 6 are not expressing your gene of interest? Answers based on regulation of gene expression in eukaryotes. Question from the field of genetics. Thank you in advance!

Answer 1

Gene is a sequence of nucleotide present in the DNA that codes a specific regulatory or functioning molecule. Gene is a part of an organism’s genome which is known to house all the coding and non-coding region of the DNA.

1. To determine the presence or absence of a gene in the genome of the yeast, two simple techniques can be performed. PCR (polymerase chain reaction) and southern hybridisation are useful in determining the presence of a gene in the genome.

The technique of PCR works on the principle of amplifying a specific set of nucleotides using a set of known primers. The primers being specific for the complimentary sequence, will bind to the specific region in the gene, absence of the gene will result in no amplified product of the desired gene. The amplified product can either by directly analysed by real time PCR or by the technique of electrophoresis to detect the presence of desired gene in the PCR product.

Southern hybridisation is performed using the complementary probes for the sequence of the gene. The probe will only bind to the complementary sequence of the gene and thus the presence of gene can be detected.

2. The reason for not expression of the gene in yeast 5 and 6 could be:

1. Absence of promoter or other regulatory element for the gene. These elements are crucial for the expression of the gene. This may result due to non-specific insertion of the gene.
2. Insertion with inversed orientation of the gene also hampers its expression. The gene must be in correct orientation to express properly.