Genetics Review: Gene Interactions, Linkage, Epigenetics, Mutations, and Chromosome Structure

Vocabulary flashcards reviewing core concepts in genetics including epistasis, linkage, epigenetics, gene mutations, DNA repair pathways, and chromosome architecture based on lecture notes 9 through 19.

Epistasis

A genetic phenomenon in which the expression of an allele at one gene locus masks or alters the phenotypic expression of alleles at a distinct gene locus.

Suppression

A genetic interaction in which a mutation in a second gene counteracts or reverses the phenotypic effect of an original mutation in a first gene, restoring the wild-type phenotype.

Sex-limited trait

A trait encoded by autosomal genes that is exclusively expressed in only one sex due to anatomical or physiological limitations.

Sex-influenced trait

A trait determined by autosomal genes whose phenotypic expression or dominance relationship differs between sexes, typically mediated by sex hormones.

Genetic anticipation

A pattern of inheritance characterized by an earlier age of onset and increasing severity of a genetic disorder across successive generations.

Genomic imprinting

An epigenetic modification causing monoallelic gene expression dependent on the parent of origin from which the allele was inherited.

Conditional mutation

A mutation that produces a wild-type phenotype under permissive environmental conditions and a mutant phenotype under restrictive conditions.

Linkage

The tendency of two or more genes located close together on the same chromosome to be transmitted together during meiosis.

Crossover

The reciprocal exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis.

Cis vs trans configuration

Linkage configurations where cis (coupling) indicates that two mutant alleles are on the same homolog, whereas trans (repulsion) indicates they reside on opposite homologs.

Mitotic recombination

A rare crossing-over event occurring during mitosis in somatic cells that can result in patches of homozygosity.

Twin spot

Adjacent patches of tissue displaying distinct, reciprocal mutant phenotypes in a heterozygous organism, resulting from mitotic recombination.

Prader-Willi syndrome

A neurogenetic disorder caused by the loss of functional paternal alleles in an imprinted region on human chromosome 15.

Angelman syndrome

A neurogenetic disorder caused by the loss of functional maternal alleles in an imprinted region on human chromosome 15.

Position effect variegation

Variable gene expression observed when a gene is relocated via chromosomal rearrangement into close proximity with heterochromatin, leading to stochastic silencing.

X chromosome inactivation

An epigenetic dosage-compensation mechanism in mammalian females where one of the two X chromosomes is transcriptionally silenced in somatic cells.

Prion

An infectious, abnormal proteinaceous particle that propagates by inducing the conformational change of normal cellular proteins into an identical misfolded state.

Transition

A base pair substitution in which a purine is replaced by another purine ($A \leftrightarrow G$) or a pyrimidine is replaced by another pyrimidine ($C \leftrightarrow T$).

Transversion

A base pair substitution in which a purine is replaced by a pyrimidine or a pyrimidine is replaced by a purine ($A/G \leftrightarrow C/T$).

Nonsense mutation

A point mutation that converts a codon specifying an amino acid into a premature stop codon, terminating protein synthesis.

Dominant negative mutation

A mutation that produces an altered gene product that acts antagonistically to the wild-type product, disrupting its function in a heterozygote.

Depurination

A spontaneous lesion involving the hydrolytic cleavage of a glycosidic bond that removes an adenine or guanine base from the DNA backbone, leaving an apurinic site.

5-bromouracil

A thymine base analog that, in its rare enol tautomeric form, mispairs with guanine instead of adenine, causing transition mutations.

Acridine orange

An intercalating chemical agent that wedges between stacked base pairs of DNA, causing distortions that lead to insertions or deletions during replication.

Ames test

A biological screening assay utilizing histidine-auxotrophic strains of Salmonella to evaluate the mutagenic and carcinogenic potential of chemical agents.

Photolyase

A light-activated DNA repair enzyme that performs direct photoreactivation repair by cleaving cyclobutane pyrimidine dimers induced by UV light.

Nucleosome

The basic repeating subunit of chromatin, consisting of roughly 146 base pairs of DNA wound around an octamer core of histone proteins.

Heterochromatin

Densely compacted, cytologically dark chromatin that is rich in repetitive DNA sequences and largely transcriptionally inert.

Kinetochore

A multiprotein complex assembled directly onto the centromeric DNA of a chromosome that serves as the attachment site for spindle microtubules during cell division.

Holocentric

Referring to chromosomes that lack a single distinct centromere and instead form microtubule attachment sites along their entire longitudinal axis.

Telomerase

A specialized ribonucleoprotein reverse transcriptase that extends chromosome ends by adding repetitive sequences using its intrinsic RNA template.