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In genetics, it is sometimes useful to classify mutations as either harmful or beneficial (or neutral): A harmful, or deleterious, mutation decreases the fitness of the organism. Many, but not all mutations in essential genes are harmful (if a mutation does not change the amino acid sequence in an essential protein, it is harmless in most cases).
This mutation, which at first glance appeared to be harmful, conferred enough of an advantage to heterozygotes to make it beneficial, so that it remained at dynamic equilibrium in the gene pool. Kalmus introduced flies with the ebony mutation to a wild-type population.
Illustration of chromosome crossover during genetic recombination. In evolutionary genetics, Muller's ratchet (named after Hermann Joseph Muller, by analogy with a ratchet effect) is a process which, in the absence of recombination (especially in an asexual population), results in an accumulation of irreversible deleterious mutations.
A related argument against evolution is that most mutations are harmful. [118] However, the vast majority of mutations are neutral, and the minority of mutations which are beneficial or harmful are often situational; a mutation that is harmful in one environment may be helpful in another. [119]
Recently reported estimates of the human genome-wide mutation rate. The human germline mutation rate is approximately 0.5×10 −9 per basepair per year. [1]In genetics, the mutation rate is the frequency of new mutations in a single gene, nucleotide sequence, or organism over time. [2]
It can also be achieved experimentally using laboratory procedures. A mutagen is a mutation-causing agent, be it chemical or physical, which results in an increased rate of mutations in an organism's genetic code. In nature mutagenesis can lead to cancer and various heritable diseases, and it is also a driving force of evolution.
Most new mutations either have a neutral or negative effect on fitness, while some have a positive effect. [11] A beneficial mutation is more likely to persist and thus have a long-term positive effect on genetic diversity. Mutation rates differ across the genome, and larger populations have greater mutation rates. [11]
Mutations happen, and they are completely random with respect to a need in the environment and fitness. Mutations can either be beneficial in which they increase an organism's fitness, neutral in which they do not affect an organism's fitness or deleterious where they negatively affect an organism's fitness.