Final answer:
A position effect can alter gene expression when a gene is moved from a less condensed, or euchromatic, chromosome, where it is active, to a highly condensed, or heterochromatic, chromosome, where its expression may be turned off.
Step-by-step explanation:
A position effect can alter gene expression when a gene is moved from a less condensed, or euchromatic, chromosome, where it is active, to a highly condensed, or heterochromatic, chromosome, where its expression may be turned off. This type of gene regulation is called epigenetic regulation, and it involves changes to the chromosomal structure to control gene expression.