The genetic code can be altered by a variety of mechanisms; alterations in the genetic code are termed mutations. Genetic changes that occur in the sex cells (sperm and egg) will be passed on to future generations (germline mutations). Mutations can also occur in the somatic cells of the organism (somatic mutations). These changes will not be passed down to future generations. The sequence of amino acids that code for a gene in the general population is termed wild type. Often there are minor differences in the code for a single gene across different populations or even with a population. These minor differences that do not alter the gene function are considered polymorphisms.
Some mutations in the genome can lead to a change in phenotype or physical attributes of the organism. Darwin used finches to describe how changes in phenotype could result in benefits to the organism, they could be detrimental, or neutral. He found that mutations that are advantageous for the organism will be selected for over time (natural selection). Organisms with positive changes to their phenotype would be more likely to reproduce and pass their improved phenotype on to the next generation. Alternatively, mutations that decrease the fitness, or the ability to survive, of the organism will be selected against. These organisms would be less likely to reproduce.
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