Mutation

Lore & Background

Mutations can involve duplication of large DNA sections through genetic recombination, providing raw material for evolving new genes. Most genes belong to larger families of shared ancestry, and novel genes arise through duplication and mutation or recombination of protein domains. For example, the human eye uses four light-sensing genes that all descended from a single ancestral gene. Changes in chromosome number, such as the fusion that produced human chromosome 2, can accelerate species divergence by reducing interbreeding. Mobile DNA sequences like transposons make up a major fraction of plant and animal genomes and can mutate or delete existing genes, producing genetic diversity.

Reader's Guide

Mutations are fundamentally different from DNA damage: a mutation is an alteration of base sequence that cannot be recognized by enzymes once present in both strands, and it is replicated when the cell replicates. DNA damage is a physical alteration that can be repaired using the complementary strand as a template. However, DNA damages often cause errors during replication or repair, which are a major source of mutations. Nonlethal mutations accumulate in the gene pool, with natural selection reducing some and favoring others. The overwhelming majority of mutations have no significant effect on fitness, while beneficial mutations can improve reproductive success. Neutral mutations can increase in frequency via genetic drift. DNA repair mechanisms and apoptotic pathways help eliminate many potentially permanent mutations.

Did You Know?

• Humans on average pass 60 new mutations to their children, with fathers passing more depending on age, adding two new mutations per year.
• More than a million copies of the Alu sequence are present in the human genome, now functioning in regulating gene expression.