Question

Explain two ways that a chromosomal rearrangement can cause a position effect.

Short answer

Two ways that a chromosomal rearrangement can cause a position effect are: 1) When a gene is relocated to a heterochromatic, or condensed, area of the chromosome leading to under-expression, and 2) The gene could move away from its necessary regulatory elements on the chromosome, leading to inappropriate expression levels. Both instances are caused by changes in the gene's physical location on the chromosome due to rearrangement.

Step-by-step solution

- Define Chromosomal Rearrangement

Chromosomal rearrangement refers to a structural alteration of a chromosome in which a part of a chromosome is shifted. There are four types of chromosomal rearrangements: inversions, deletions, duplications and translocations.

- Define Position Effect

The position effect refers to the change in the expression of a gene as a result of change in its location on a chromosome. Often, this change in position can cause a gene to be repressed or overexpressed.

- Explain first way chromosomal rearrangement can cause position effect

The first way chromosomal rearrangement might cause a position effect is through a relocation of a gene into an area of the chromosome that is heterochromatic, or condensed. These regions are less transcriptionally active, and as such, the gene could become expressed at lower levels than it would have otherwise if it were in a position conducive to transcription.

- Explain second way chromosomal rearrangement can cause position effect

The second way chromosomal rearrangement might cause a position effect is by moving a gene away from crucial regulatory elements on the chromosome. These elements help regulate the expression of the gene, and by being moved away from them, the gene could be expressed at inappropriate levels, or not at all. The fresh position of the gene places them under the control of new elements that may not be typically associated with their control.