DNA from a strain of bacteria with genotype a + , b + , c + , d + , e + was isol
ID: 50101 • Letter: D
Question
DNA from a strain of bacteria with genotype a+, b+, c+, d+, e+ was isolated, fragmented, and used to transform a bacterial strain that was a--, b--, c--, d--, e--. The transformed cells were tested for the presence of donated genes.
a. When two genes are found to be cotransformed in such experiments involving fragmented DNA, this is likely due to their close proximity on the bacterial chromosome. Why is cotransformation of distantly related genes possible but rare.
b. If the following genes were found to be cotransformed,(but not the other possible combinations), what is the order of the genes on the bacterial chromosome?
a+ and d+
b+ and e+
c+ and d+
c+ and e+
Explanation / Answer
Answer a) As we know that Transformation is a process of directly transferring a genetic material into the cell. while co-transformation is a process of transferring two genes of interest at the same time. it becomes easy to co-transform two different genes when they are located closely on the same chromosomal fragment. when two genes are located far apart, it becomes hard to transform such large fragment of DNA so we fragment the DNA into smaller pieces. in such case, the genes located nearby will be transformed easily while the frequency of co-transformation of two genes present on two different segments of far apart will decrease many times. it makes the cotransformation of distantly related genes possible, but rare.
Answer b) As we know that two genes located closely tend to be cotransformed easily. use this information to find out the possible combinations.
initial possible combinations would be; ad, be, cd, ce.
it can be rearranged as ad, be, dce.
further rearrangement would give us adceb.
therefore, adceb is the final order for the given genes on the bacterial chromosomes.
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