Chapter 09: Gene Expression - The Effects of Mutations on Gene Expression and Function

Vocabulary flashcards covering the effects of mutations on gene expression, coding sequences, and protein function based on Chapter 09.

Silent mutation

A mutation in the coding sequence of a gene that does not alter the amino acid sequence of the polypeptide, due to the degenerate nature of the genetic code.

Missense mutation

A mutation in the coding sequence of a gene that replaces one amino acid in the polypeptide with another.

Conservative missense mutation

A missense mutation where the chemical properties of the substituted amino acid are similar to the original amino acid (such as negatively charged aspartic acid replaced by negatively charged glutamic acid).

Nonconservative missense mutation

A missense mutation where the chemical properties of the substituted amino acid differ from those of the original amino acid (such as negatively charged aspartic acid replaced by uncharged alanine).

Nonsense mutation

A mutation that alters an amino acid-encoding codon into a translation stop codon ($UGA$, $UAG$, or $UAA$), resulting in a truncated, nonfunctional polypeptide.

Frameshift mutation

A mutation caused by the insertion or deletion of a number of nucleotides that is not a multiple of three within the coding region, altering the translational reading frame downstream.

Amorphic (null) mutation

A loss-of-function mutation that completely blocks the function of a gene product (for example, the deletion of an entire gene); typically recessive to wild-type.

Hypomorphic (leaky) mutation

A loss-of-function mutation that produces a reduced amount of the wild-type protein or a protein with reduced activity; typically recessive to wild-type.

Incomplete dominance (loss-of-function)

A genetic condition in which the phenotype varies continuously with the amount of functional gene product produced by the alleles.

Haploinsufficiency

A phenomenon where a single wild-type allele cannot produce sufficient gene product to prevent a mutant phenotype, causing a loss-of-function allele to be dominant (such as in $GLI3 / GLI3^+$ polydactyly).

Hypermorphic mutation

A gain-of-function mutation that produces either an increased quantity of gene product or a gene product that is more active or efficient (such as the constitutively active $FGFR3$ receptor in achondroplasia).

Neomorphic mutation

A gain-of-function mutation that produces a gene product with a novel function or causes normal product to be expressed at an inappropriate time or ectopic location.

Ectopic expression

The expression of a gene in an abnormal tissue location or developmental time point, such as Antp protein being expressed in antenna precursor cells due to the $Antp^{Ns}$ mutation.

Antimorphic (dominant negative) allele

A mutant allele encoding a defective subunit that binds to and inactivates the normal wild-type subunits within a multimeric protein complex.

Nonencoding genes

Genes transcribed into functional RNAs (such as rRNAs, tRNAs, and snRNAs) but not translated into proteins; mutations within them can have global cellular effects and are frequently homozygous lethal.

Nonsense-suppressor tRNA

A mutant transfer RNA with an altered anticodon that base-pairs with a premature stop codon, enabling an amino acid to be incorporated and allowing full-length translation of a nonsense mutant mRNA.