Yeast Peptone Synthesis Lab Report

For Yeast Peptone Dextrose (YPD) plate, 2000, 4000 and 6000 colonies were observed when there was 0.2g/ml, 0.4g/ml and 0.6g/ml of tartrazine and carmoisine from the yellow food dye respectively. All the colonies observed were white. For Tryptophan lacking (TRP-) plate, 5, 13 and 87 colonies were observed when there was 0.2g/ml, 0.4g/ml and 0.6g/ml of tartrazine and carmoisine from the yellow food dye respectively. Similarly, all the colonies observed were white. For Isoleucine lacking (Iso-) plate, 8, 13 and 57 colonies were observed when there was 0.2g/ml, 0.4g/ml and 0.6g/ml of tartrazine and carmoisine from the yellow food dye respectively. Yet again, all the colonies observed were white.

For the negative control, 220 white colonies were

This indicates a mitotic crossing over. On the other hand, when 2% EMS was used, 235 white colonies and 1 pink colony were observed. This indicates a recombinational repair. However, when 3% EMS was used, 240 white colonies were observed. EMS is known to cause transversion mutations (Winston, F. 2001). A transversion mutation is a point mutation whereby the pyrimidine and purine nucleotides are reversed. In addition, there is an inverse relationship between mutagenic concentrations of EMS and the number of colonies observed. As the concentration of mutagenic EMS increases, the number of colonies decreases. This suggests that higher concentrations of EMS results in a greater extent of mutations or multiple mutations (Winston, F. 2001). This causes the death of the yeast cells which then translates to a lower number of colonies

This shows that there is no definite outcome of recombinational repair or mitotic crossing over caused by the mutagens, tartrazine and carmoisine. If tartrazine and carmoisine causes mitotic crossing over, then the homoallelic ade2 loci: ade2-40/ade2-40 would lead to an obstruction to the adenine pathway which then results in the formation of red colonies. However ade2-119/ade2-119 would result in the formation of pink colonies. The presence of pink-white and red-white colonies suggests that the crossing over between the ade2 loci and the centromere has taken place. However the exponential growth of the colonies and the presence of clumping were due to excess amounts of mixture added to the plates. A smaller amount of 0.5ml would have sufficed.

On the TRP- and Iso- plates, growth was observed under all three concentrations of tartrazine and carmoisine (0.2g/ml, 0.4g/ml, and 0.6g/ml). This shows that tartrazine and carmoisine were able cause mutation in the yeast cells. This could include reverse point mutation and mitotic gene conversion. These mutations could have resulted in the yeast cell’s ability to synthesize its very own tryptophan and isoleucine which is vital to its growth. Thus it is able to grow on both mediums even though each plate lacked tryptophan and isoleucine