Why Mutations Are the Source of New Genetic Variation
Genetic variation is essential for evolution, adaptation, and the diversity we see across species. At the heart of this variation is mutation—the process that creates new alleles. An allele is simply a version of a gene, and mutations provide fresh versions that may alter phenotypes or influence how organisms respond to their environment. Understanding how mutations arise and generate new alleles is crucial for IB Biology students studying genetics and evolution.
A mutation is a change in the DNA nucleotide sequence. These changes can occur spontaneously during DNA replication or be triggered by external factors such as radiation, chemicals, or errors in DNA repair. When a mutation occurs in a gene, it may alter the gene’s base sequence, producing a new allele.
One common type is the point mutation, where a single nucleotide is replaced by another. If this substitution changes the codon, it may change the amino acid encoded, producing a new version of the protein. Even a single amino acid change can alter protein function, potentially creating a new phenotype. For example, the allele responsible for sickle-cell anemia originated from a single base substitution.
Other mutations involve insertions or deletions of nucleotides. These can cause frameshift mutations, drastically altering the reading frame of the gene and resulting in completely different proteins. Such mutations often produce nonfunctional alleles but can occasionally generate new beneficial functions.
Larger mutations, such as duplications, can also create new alleles. Gene duplication provides a copy of a gene that is free to accumulate mutations without affecting the original gene’s function. Over time, duplicated genes may evolve new roles—a major driver of evolutionary innovation.
Importantly, not all mutations change phenotypes. Silent mutations alter DNA sequences without affecting amino acids. Neutral mutations may change amino acids without altering protein function. Nonetheless, these silent or neutral changes still create new alleles that contribute to genetic diversity.
For mutations to create alleles that are passed to offspring, they must occur in gamete-forming cells. Mutations in somatic cells do not enter the gene pool and therefore do not create heritable variation.
Once new alleles arise, they may increase, decrease, or have no effect on fitness. Natural selection determines whether they spread in a population. Some alleles persist because they offer a selective advantage, whereas others remain rare or disappear.
In summary, DNA mutations introduce new genetic possibilities, making them the ultimate source of biological diversity.
FAQs
Do all mutations create new alleles?
Yes. Any change in the nucleotide sequence produces a new allele, though many alleles may have no observable effect on phenotype.
Are mutations always harmful?
No. Many mutations are neutral or beneficial. Harmful mutations occur, but beneficial ones can lead to evolutionary advantages.
How do mutations become part of a population’s gene pool?
Mutations must occur in gametes and be passed to offspring. If they persist through generations, they become part of the gene pool.
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