Final answer:
More than half of all spontaneous mutations in Drosophila result from insertion of a nucleotide in or near a functional gene. Insertion mutations can alter gene expression or protein function and may result in frameshift mutations.
Step-by-step explanation:
More than half of all spontaneous mutations in Drosophila result from insertion of a nucleotide in or near a functional gene.
Insertion mutations occur when one or more nucleotides are added to the DNA sequence. In Drosophila, these insertions can happen in or near functional genes, causing changes in the gene's expression or protein function.
For example, if an insertion occurs within a coding sequence, it can alter the reading frame of the genetic code, resulting in a frameshift mutation. This alters the amino acid sequence of the protein and often leads to a nonfunctional protein.