# 4.S: Mutation and Variation (Summary)

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• When a variation in DNA sequence originated recently, and is rare in a population, we call that change a mutation.
• When variations in DNA sequence co-exist in a population, and neither one can be meaningfully defined as wild-type, we call the variations polymorphisms.
• Mutations may either occur spontaneously, or may be induced by exposure to mutagens.
• Mutations may result in either substitutions, deletions, or insertions.
• Mutation usually causes either a partial or complete loss of function, but sometimes results in a gain of function,including new functions.
• Spontaneous mutations arise from many sources including natural errors in DNA replication, usually associated with base mispairing, or else insertion deletion especially within repetitive sequences.
• Induced mutations result from mispairing, DNA damage, or sequence interruptions caused by chemical, biological, or physical mutagens.
• By randomly inducing mutations, then screening for a specific phenotype, it is possible to identify genes associated with specific biological pathways.
• Transposable elements are dynamic, abundant components of eukaryotic genomes and important forces in evolution.
• Transposable elements are dynamic, abundant components of eukaryotic genomes and important forces in evolution.
• The efficiency of mutant screening is limited by silent mutations, redundancy, and embyronic lethality.
• Mutation of different genes can produce a similar phenotype.
• Complementation testing determines whether two mutants are the result of mutation of the same gene (allelic mutations), or if each mutant is caused by mutation of a different gene (non-allelic mutations).

## Key Terms

 mutation mutant polymorphism insertion deletion substitution mutagen DNA replication error Strand slippage biological mutagen chemical mutagen physical mutagen mispairing loop SSR insertional mutagen Class I, Class II transposon retrotransposon reverse transcriptase transposase non-autonomous autonomous SINE, LINE, Alu P-element T-DNA copy-and-paste cut-and-paste alkylation agent EMS intercalating agent benzopyrene carcinogenic ethidium bromide thymine dimer mutant screen loss-of-function gain-of-function amorph null hypomorph hypermorph neopmorph dominant negative somatic cells germline cells silent mutation inter-genic region redundancy essential gene recessive lethal allele complementation testing allelic / non-allelic cM0, M1, M2 redundancy lethality allelic non-allelic complementation group CFTR Cystic Fibrosis (CF) DF508(PHE508DEL) Kalydeco

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