Mutation Definition and Forms

Mutation – permanent alterations in the allele pairings, or genes, on the chromosomes that pass on to new cells and ultimately to offspring. Mutations are the process through which genetic change takes place. Some mutations are beneficial, some are neutral, and some are harmful. Mutations occur as changes in the gene’s nucleotide sequences. These changes may take the form of

  • Point mutations, also called base mutations, which are analogous to changing one letter in a word and occur when one nucleotide substitutes for another
  • Deletion mutations, which are analogous to removing a word from a sentence and occur when the gene drops a nucleotide sequence
  • Insertion mutations, which are analogous to adding a word to a sentence and occur when the gene adds a nucleotide sequence
  • Increased repeat mutations, which occur when a normally repeated nucleotide repeats extra times

A germline mutation affects a gamete (ovum or spermatozoon) or zygote and is present from conception, passing to the child. Wilms’s tumor and hemophilia are examples of germline mutations that cause disease. A monogenic mutation affects a single gene. Duchenne’s muscular dystrophy and sickle cell disease are among the conditions that occur as a result of monogenic mutations.

Polygenic mutations involve multiple alleles of numerous genes, often across chromosomes. Polygenic mutations often do not clearly result in genetic disorders though establish genetic predisposition. Conditions such as cardiovascular disease (cvd), diabetes, and some types of cancer occur as a result of polygenic mutations in combination with lifestyle (environmental) factors.


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