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1. An average; a number that in some sense represents the central value of a set of numbers.
2. Arithmetic mean.
3. In probability and statistics, the expected value (mathematical expectation) of a random variable, the limiting value to which the sample mean converges as the sample size is increased indefinitely (if the limit exists).
1. Changes in form, quality, or some other characteristic.
2. In genetics, permanent transmissible changes in the genetic material, usually in a single gene.
See definitions for individual types of mutations under "mutation."
A segment of a DNA molecule that contains all the information required for synthesis of a product (polypeptide chain or RNA molecule), including both coding and non-coding sequences. It is the biological unit of heredity, self-reproducing, and transmitted from parent to progeny. Each gene has a specific position (locus) on the chromosome map. From the standpoint of function, genes are conceived of as structural, operator, and regulatory genes.
wild-type gene - The normal allele of a gene, sometimes symbolized by +.
X-linked gene - A gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. X linkage is used sometimes synonymously with sex linkage since no genetic disorders have as yet been associated with genes on the Y chromosome.
1. A change in form, quality, or some other characteristic.
2. In genetics, a permanent transmissible change in the genetic material, usually in a single gene.
frameshift mutation - A mutation resulting from an addition or subtraction that is not an exact multiple of 3 base pairs in a coding sequence. From the point of mutation onwards, base triplets (codons) are read out of phase; the reading frame of the gene is changed, and a completely different set of amino acids is made into protein.
loss-of-function mutation - Impairment of the function of a gene caused by mutation.
missense mutation - A mutation that changes a codon so that it codes for a different amino acid.
nonsense mutation - A mutation in which one of the three terminator codons in the mRNA (UAG, amber; UAA, ochre; UGA, umber or opal), used to signal the end of a polypeptide, appears in the middle of a genetic message, causes premature termination of transcription, and releases incomplete, generally nonfunctional polypeptides from the ribosome.
point mutation - A mutation resulting from a change in a single base pair in the DNA molecule, caused by the substitution of one nucleotide for another.
In the singular: A segment of a DNA molecule that contains all the information required for synthesis of a product (polypeptide chain or RNA molecule), including both coding and non-coding sequences. It is the biological unit of heredity, self-reproducing, and transmitted from parent to progeny. Each gene has a specific position (locus) on the chromosome map. From the standpoint of function, genes are conceived of as structural, operator, and regulatory genes.
wild-type gene - The normal allele of a gene, sometimes symbolized by +.
X-linked gene - A gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. X linkage is used sometimes synonymously with sex linkage since no genetic disorders have as yet been associated with genes on the Y chromosome.
