DNA from a strain of bacteria with genotype a⁺ b⁻ c⁺ d⁺ e⁻ was isolated and used to transform a strain of bacteria that was a⁻ b⁻ c⁻ d⁻ e⁻. The transformants were tested for the presence of donated genes. The following genes were co-transformed:

a⁺ and c⁺   b⁺ and d⁺  e⁺ and d⁺  c⁺ and b⁺

which one of the following options given correct order of genes on the bacterial chromosome?

Correct option is B

Explanation:

In co-transformation experiments, genes that are closer together on the chromosome tend to be co-transformed more frequently than genes that are farther apart. Based on the information provided:

• The gene pairs a+ and c+ and b+ and d+ co-transformed, suggesting that these gene pairs are physically closer to each other on the chromosome.

• The co-transformation of e+ and d+ and c+ and b+ indicates that these gene pairs are also close to each other.

When you map the genes based on co-transformation frequency and proximity, the genes appear to be ordered as a c b d e, which is consistent with the observation that a is closest to c, followed by b, then d, and finally e.

Information Booster:

1. Co-transformation is a powerful method used in gene mapping to determine the relative positions of genes on a chromosome.

2. Genes that are closer together on the chromosome tend to be co-transformed at higher frequencies, as they are more likely to be transferred together during genetic exchange.

3. The order of genes can be determined based on the frequency of co-transformation, where genes that co-transform most frequently are likely to be closer together on the chromosome.

Additional Knowledge:

• Option 1 (a c d b e) would suggest a different ordering that doesn’t match the observed co-transformation frequencies.

• Option 3 (b d c a e) and Option 4 (e d c a b) also provide incorrect gene orders based on the co-transformation data given in the problem.