Synthesis question applying ideas of dominance In the first

Synthesis question applying ideas of dominance. In the first section of this course, we discussed an experiment performed by Frederick Griffiths in 1928 with two strains of Pneumococcus bacteria, called the Smooth strain and the Rough strain. The Smooth strain was the wild-type strain. It formed a smooth polysaccharide coat which enabled it to be infectious in mice. The Rough strain was a spontaneous mutant that arose when Griffith was growing the Smooth strain on agar plates. The Rough strain could not make the polysaccharide coat due to a mutation in the coat gene called C, and as a result, it was not infectious in mice. A mutant allele of C called CR. Results in the Rough strain, because it results in a failure of the bacteria to make a polysaccharide coat. As you may recall, Griffith s exciting observation was that he could convert the R strain to the S strain by mixing R strain bacteria with heat-killed S strain bacteria. In essence. Griffith had \"transformed\" the R strain with a wild-type copy of the C gene from the S strain, called Cs. Bacteria are normally haploid. However, in the transformation experiment, the R-strain bacteria ended up with a second copy of the C gene: they had both the C allele and the Cs allele. Which allele of C is dominant in regard to the ability of bacteria to make the polysaccharide coat? Circle: CR or Cs Explain in one sentence the data (from the description above) that supports your answer. Is CR likely to be a dominant-negative mutation? Circle Yes or No. Explain in one sentence the data (from the description above) that supports your answer.

Solution

Please find the answers below:

Part A: As it can be seen from the information, mixing of smooth-allele with rough-allele transforms the rough-cells to become smooth in texture. This happens because expression of the smooth allele made the cells to synthesize the carbohydrate envelope and thus the cells appeared smooth in texture. Since only a single copy of C^S was introduced in the cell, it can be clearly deduced that the C^S allele is dominant over the C^R allele.

Part B: No.

Reason: C^R does not correspond to a dominant-negative mutation because in the presence of C^S allele, the C^R allele is suppressed and the bacteria do produce a carbohydrate coat. (This can be deduced from the observation that mixing of C^S strains with C^R strains lead to conversion of C^R to C^S strains)