(T/F) Chromosomal changes that delete, disrupt, or rearrange many loci at once are almost certain to be harmful. However, when such large-scale mutations leave gene intact, their effects on organisms may be neutral. In rare cases, chromosomal rearrangements may even be beneficial.
An important source of variation begins when genes are duplicated due to errors in meiosis (such as unequal crossing over), slippage during DNA replication, or the activities of transposable elements.
Gene duplications that do not have severe effects can persist over generations, allowing mutations to accumulate. The result is an expanded genome with new loci that may take on new functions. Such beneficial increases in gene number appear to have played a major role in evolution.
For instance, the remote ancestors of mammals carried a single gene for detecting oders that has been duplicated many times. As a result, humans today have about 1,000 olfactory receptor genes, and mice have 1,300.