In genetics, a<unk>  is an unstable heritable element where the probability of expression of a mutant phenotype is a function of the number of copies of the<unk> . That is, the replication product (progeny) of a<unk>  has a different likelihood of<unk>  than its predecessor. These<unk> s, typically short sequences repeated many times, give rise to numerous known diseases, including the trinucleotide repeat disorders. Robert I. Richards and Grant R. Sutherland called these phenomena, in the framework of<unk> al genetics,<unk> s. Triplet expansion is caused by slippage during DNA replication. Due to the repetitive nature of the DNA sequence in these regions , 'loop out' structures may form during DNA replication while maintaining complementary base pairing between the parent strand and daughter strand being synthesized. If the loop out structure is formed from sequence on the daughter strand this will result in an increase in the number of repeats. However, if the loop out structure is formed on the parent strand a decrease in the number of repeats occurs. It appears that expansion of these repeats is more common than reduction. Generally the larger the expansion the more likely they are to cause disease or increase the severity of disease. This property results in the characteristic of anticipation seen in trinucleotide repeat disorders. Anticipation describes the tendency of age of onset to decrease and severity of symptoms to increase through successive generations of an affected family due to the expansion of these repeats.
Dynamic mutation
Antineoplastic resistance
Genetic heterogeneity
Allelic heterogeneity
Phenotypic heterogeneity
Cancer selection
Heteroplasmy
Sex selection