Genetics glossary

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:

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A

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.

B

Base pair: A pair of nucleotide bases on complementary DNA or RNA strands organized in a double helix.

C

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.
Codon: Series of three (3) DNA or RNA nucleotides in a gene that code for a particular amino acid or stop signal during protein synthesis. DNA and RNA molecules are written in a language of four nucleotides; meanwhile, the language of proteins includes 20 amino acids. Codons provide the key that allows these two languages to be translated into each other. Each codon corresponds to a single amino acid (or stop signal), and the full set of codons is called the genetic code. The genetic code includes 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides. Of the 64 codons, 61 represent amino acids, and three are stop signals. For example, the codon CAG represents the amino acid glutamine, and TAA is a stop codon. The genetic code is described as degenerate, or redundant, because a single amino acid may be coded for by more than one codon. When codons are read from the nucleotide sequence, they are read in succession and do not overlap with one another.
Cytosine: One of the four nucleotide bases in DNA or RNA; pairs with guanine.

D

DNA: A polymeric molecule made of deoxyribonucleotides, hence then name deoxyribonucleic acid. Most often has the form of a "double helix", which consists of two paired DNA molecules and resembles a ladder that has been twisted. The "rungs" of the ladder are made of base pairs, or nucleotides with complementary hydrogen bonding patterns.

G

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.
Gene expression: The process in which the information encoded in a gene is converted into a form useful for the cell. The first step is transcription, which produces a messenger RNA molecule complementary to the DNA molecule on which a gene is encoded. For protein-coding genes, the second step is translation, in which the messenger RNA is read by the ribosome to produce a protein.
Gene pool: the sum of all the alleles shared by members of a single population.
Genetics: the field of biology that studies genes and their inheritance.
Genotype: The complement of alleles present in a particular individual's genome that give rise to the individual's phenotype.
Genome: The entire complement of genetic material in the chromosome set of an organism, virus or organelle.
Guanine: One of the four nucleotide bases in DNA or RNA; pairs with cytosine.

L

Locus: a location on a chromosome where a particular gene resides.

M

Mutation: is a change in the base pair sequence of DNA or RNA.

N

Nucleic Acid:A nucleic acid is a long molecule made up of smaller molecules called nucleotides. Nucleic acids are macromolecules, which means they are molecules composed of many smaller molecular units. These units are called nucleotides, and they are chemically linked to one another in a chain. The order, or sequence, of the nucleotides in DNA allows nucleic acid to encode an organism's genetic blueprint. Along with DNA, the other major type of nucleic acid in cells is ribonucleic acid (RNA). DNA differs from RNA by its inclusion of thymine (T), whereas RNA differs from DNA by its inclusion of uracil (U). In DNA, the nucleotides are referred to in shorthand as A, C, T, and G. In RNA, the nucleotides are A, C, U, and G.
Nucleotide: organic molecules that serve as the monomers, or subunits, of nucleic acids like DNA and RNA. They include adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U).

P

Phenotype: The observable physical or behavioral traits of an organism, largely determined by the organism's genotype.
Protein: A linear polymeric molecule made of amino acids linked by peptide bonds. Proteins carry out the majority of chemical reactions that occur inside the cell.

T

Thymine: One of the four nucleotide bases in DNA; pairs with adenine. In RNA, thymine is replaced with uracil.
Transcription: The first step in gene expression, in which a messenger RNA molecule complementary to particular gene encoded in DNA is synthesized by enzymes called RNA polymerases. To produce a functional protein, transcription is followed by translation.
Translation: The second step in gene expression, in which a messenger RNA molecule is read by the ribosome to produce a functional protein. Translation is always preceded by transcription.

U

Uracil: One of the four nucleotide bases in RNA; pairs with adenine, In DNA, uracil is replaced with thymine.

Genetics glossary

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See also

Further reading