What is the mutation?
Take a look at how the variation occurs.
The mutation generates new alleles
The whole human family is a species with the same genes. The mutation creates slightly different versions of the same genes, called alleles. These small differences in DNA sequence make each individual unique. They explain the variation we see in human hair color, skin color, size, shape, behavior, and susceptibility to disease. Individuals of other species also vary, both in physical appearance and behavior.
Genetic variation is useful because it helps populations change over time. Variations that help an organism survive and reproduce are passed on to the next generation. Variations that hinder survival and reproduction are eliminated from the population. This process of natural selection can lead to significant changes in the appearance, behavior or physiology of individuals in a population in just a few generations.
Once new alleles appear, meiosis and sexual reproduction combine different alleles in new ways to increase genetic variation.
Mutation vs. variation
It is helpful to think of mutation as a process that creates genetic variation. We often refer to a mutation as one thing – the genetic variation itself. This approach can be useful when dealing with a gene associated with a disease: the disease allele carries a mutation, a change in the DNA that compromises the function of the protein. However, this approach gives mutation a bad name.
It is important to remember that the loss of gene function does not always affect health. For example, most mammals have hundreds of genes that code for olfactory receptors, proteins that help us smell. Losing one of these genes probably doesn’t make much difference.
Unlike the variations that cause disease, there are many other examples of variations that are neither good nor bad, but simply different, such as blood types and eye color. Just as with disease alleles, the process of mutation creates these more neutral variations. But with neutral variations, it can be impossible to tell which allele is the “normal” allele that existed first and which is the “mutant” – and the distinction is often meaningless.
Proteins and switches
The mutation creates variations in the protein-coding parts of genes that can affect the protein itself. But even more often, it creates variations in the “switches” that control when and where a protein is active and how much protein is made.
Lactase is an enzyme that helps infants break down lactose, a milk sugar. Normally, the gene that codes for lactase is active in babies and then turned off around the age of four. When people who don’t make lactase consume milk, they experience gas, nausea, and discomfort. But some people have a variation in a genetic switch that keeps the lactase gene active. This variation is called “lactase persistence” and people who suffer from it can retain milk in their diet even into adulthood.
Other drivers of mutation:
Environmental agents
Radiation, chemicals, by-products of cellular metabolism, free radicals, ultraviolet rays from the sun, these agents damage thousands of nucleotides in each of our cells every day. They affect the nucleotides themselves: converting one base into another, knocking a base off its backbone, or even causing a DNA strand break.
DNA Repair
Most of the time, the mutation is reversed. DNA repair machinery is constantly at work in our cells, repairing mismatched nucleotides and re-splicing broken DNA strands. Yet, some DNA changes remain. If a cell accumulates too many changes—if its DNA is so damaged that repair machinery can’t repair it—it either stops dividing or it self-destructs. If any of these processes go wrong, the cell can become cancerous.
When we put on sunscreen, we protect ourselves against mutating somatic cells, the cells that make up the body and are not involved in reproduction. . Believe it or not, a certain negligence is built into the system. Without mutation there would be no variation, and without variation there would be no evolution.
References
- Baer, C. F., Miyamoto, M. M., & Denver, D. R. (2007). Mutation rate variation in multicellular eukaryotes: causes and consequences. Nature Reviews Genetics, 8(8), 619-631.
- Barnes, D. E., & Lindahl, T. (2004). Repair and genetic consequences of endogenous DNA base damage in mammalian cells. Annu. Rev. Genet., 38, 445-476.
- Campbell, C. D., & Eichler, E. E. (2013). Properties and rates of germline mutations in humans. Trends in Genetics, 29(10), 575-584.
- Hoeijmakers, J. H. (2009). DNA damage, aging, and cancer. New England Journal of Medicine, 361(15), 1475-1485.
- Jackson, S. P., & Bartek, J. (2009). The DNA-damage response in human biology and disease. Nature, 461(7267), 1071-1078.
- Roach, J. C., Glusman, G., Smit, A. F., Huff, C. D., Hubley, R., Shannon, P. T., … & Shendure, J. (2010). Analysis of genetic inheritance in a family quartet by whole-genome sequencing. Science, 328(5978), 636-639. doi:10.1126/science.1186802