Question

Rosalind Franklin spent countless hours in the lab solving the structure of DNA. We know that X-rays cause DNA to break in half.

A) Which of the following chromosomal rearrangement likely occurred in her cells: deletion, duplication, inversion, or translocation?

B) Explain how this could lead to a position effect on gene expression.

Answer 1

A: Translocation

Many studies report significant increases in chromosome translocations, in individuals with an increasing number of cumulative diagnostic X-ray exposures.

B: Position effect is the effect on the expression of a gene when its location in a chromosome is changed, often by translocation. Each gene in the genome is located in a particular context. Its particular location in the genome enables its regulation of expression by appropriate control elements located either upstream or downstream of the gene.When a gene is ranslocated to a new chromosome its expression pattern is mostl likely to change because the gene is now under the regulation of a new set of regulatory elements. An example is provided by the position effect variegation i Drosophila.

The centromeric repetitive satellite DNA exists as heterochromatin whose heterochromatization is sequence dependent. But the formation of heterochromatin is not always sequence dependent. For example, when a gene is transferred by some method (for example – translocation) into a position adjacent to heterochromatin, it may become inactivated due to its new location probably that it has become heterochromatic.