Genetics glossary

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This is a glossary of terms commonly used in the study of genetics and related disciplines in biology. It is intended as introductory material for novices; for more specific and technical detail, please see the article corresponding to each term. Introductory articles in the field include:


  • Adenine: One of the four nucleotide bases in DNA or RNA; pairs with thymine in DNA or uracil in RNA.
  • Allele: one of multiple alternative forms of a single gene, each of which is a viable DNA sequence occupying a given position, or locus on a chromosome. For example, in humans, one allele of the eye-color gene produces blue eyes and another allele of the eye-color gene produces brown eyes.
  • Affected relative pair: An affected relative pair consists of two organisms related genetically that are both affected by the same trait. For example, two cousins who both have blue eyes are an affected relative pair since they are both affected by the allele coding for blue eyes.



  • Chromosome: a molecular "package" for carrying DNA in cells, organized as two double-helical DNA molecules that encode many genes. Some simple organisms have only one chromosome made of circular DNA, while most eukaryotes have multiple chromosomes made of linear DNA.
  • Cytosine: One of the four nucleotide bases in DNA or RNA; pairs with guanine.



  • Gene: A set of segments of nucleic acid that contains the information necessary to produce a functional RNA product in a controlled manner. In living organisms, it is a unit of heredity and typically encoded in DNA. A particular gene can have multiple different forms, or alleles, which are defined by different sequences of DNA.
  • Genetics: the field of biology that studies genes and their inheritance.




  • Nucleotide: one of the four monomers that make up a DNA molecule.