Genetics

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was fairly difficult at that time, so other methods were used to analyze their movement and structure. The following questions are inspired by the series of experiments that showed that more than one type of transposable element exists, which move by different mechanisms, but the exact data have been heavily modified. Two elements were found in yeast, called element A and element B. The sizes of the native unmodified elements are represented in the diagram of the agarose gel below (lanes 1 and 3). The investigator inserted an intron of 500 bp into a copy of each element, which he called Aint and Bint; the sizes of each element with the intron inserted are also shown in the gel (lanes 2 and 4). He introduced Aint into one yeast cell and Bint into a different cell, and grew up the cultures separately, allowing Aint and Bint to move. He then selected for mutants in which the element had inserted into the ura3 gene and disrupted its function. He then isolated the disrupted ura3 gene from each culture and analyzed its size. The results are also shown on the gel (lanes 5, 6 and 7)

A. What can be learned from this experiment about the mechanisms by which A elements and B elements transpose?

 Cut- paste mechanism & copy- paste mechanism

B. The A and the B elements have now been sequenced so their DNA sequences and sequence-related structures are known. What are some of the sequence or structural features that distinguish the two types of elements from each other?

 Long term repeats and terminal inverted repeats

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