Hypothesis I The same histidine synthesis gene is defective

Hypothesis I: The same histidine synthesis gene is defective in both strains B and C.  

Hypothesis II: Different histidine synthesis genes are defective in strains B and C.  

Results:

Strain

Growth on SD + HIS

Growth on SD

B

-

-

C

+

-

B x C

+

+

In Question Set 4, two hypotheses were discussed regarding the HIS mutations in strains B and C. Do your SD plate and SD+HIS plate results support Hypothesis I or Hypothesis II from Question Set 4?

3. A. ) Keeping in mind your answer to question #2 above, what is the predicted genotype of the diploid arising from the BxC mating?       

B. ) Can you explain your SD plate and SD+HIS plate results in regards to the URA and LEU genotype of the new diploid that you have made?  

Solution

2C)

The results observed on both SD plate and SD+His plate support the hypothesis II. The strains B and C are defective in different genes in biosynthesis of Histidine. This can be evident by the results. The strain B is not shown growth in Sd and SD+His plates. The strain C has shown growth in Sd +His plates only. The mating between strains B and C had shown growth in both SD and SD + His plates.

3A)

The genotype produced from cross betwee B and C strains is SD^- His⁺ .

3B)

The genotype URA⁺ Leu⁺ grows on both SD and SD +His plate because, the strain can synthesize histidine gene (His⁺). The genotype URA^- Leu^- cannot grow on both SD and SD and SD +His plate because the strain lacke histidine gene (His^-).