BIO 2010: Large Scale Chromosomal Changes

Vocabulary practice flashcards covering large-scale chromosomal changes, including variation in chromosome number (aneuploidy, polyploidy, euploidy) and alterations in chromosome structure (deletions, duplications, inversions, and translocations).

Aneuploidy

A variation in chromosome number involving one or a few individual chromosomes (e.g., monosomy or trisomy), resulting from nondisjunction during meiosis.

Euploidy

A variation in chromosome number involving changes in complete sets or multiples of the basic set of chromosomes (e.g., monoploidy or polyploidy).

Monoploidy

The condition of possessing only one set of chromosomes ($1n$) in an organism that is normally diploid, as seen in male bees, wasps, and ants.

Parthenogenesis

The development of an unfertilized egg into an embryo in the absence of fertilization, producing monoploid male insects such as wasps, bees, and ants.

Polyploidy

The condition of having multiple complete sets of chromosomes ($3n$, $4n$, $5n$, etc.); it is especially common in plants and typically increases cell and organ size.

Autopolyploid

A polyploid that arises from chromosome duplication within a single species (e.g., doubling from $2n$ to $4n$).

Allopolyploid

A polyploid produced by the hybridization of different, closely related species; allopolyploids are often fertile because the homeologous genomes segregate independently.

Homeologous Chromosomes

Non-identical chromosome sets derived from different ancestral species in an allopolyploid that are only partly homologous.

Colchicine

A medication extracted from Colchicum autumnale (autumn crocus) used to treat gout; in genetics, it disrupts mitotic spindle-fiber formation during metaphase and anaphase, preventing chromatid migration and creating a tetraploid ($4n$) cell from a diploid ($2n$).

Amphidiploid

A fertile allopolyploid plant possessing the sum of the chromosome numbers of two parental species, created through the doubling of chromosomes in an otherwise sterile hybrid.

Bread Wheat (Triticum aestivum)

An allohexaploid crop ($6x$, $2n = 42$) composed of three distinct grass genomes ($A$, $B$, and $D$, each with $n = 7$) that originated via natural crosses in the Fertile Crescent.

Nondisjunction

The failure of paired homologous chromosomes or sister chromatids to separate properly during first or second meiotic division, generating aneuploid gametes ($n + 1$ and $n - 1$).

Hypoploid

An aneuploid state in which one or more chromosomes or chromosomal segments are underrepresented relative to the normal complement.

Hyperploid

An aneuploid state in which one or more chromosomes or chromosomal segments are overrepresented relative to the normal complement.

Nullisomy

The loss of both members of a homologous pair of chromosomes, represented by the chromosomal constitution $2n - 2$.

Monosomy

The loss of a single chromosome from a diploid set, represented by the chromosomal constitution $2n - 1$.

Trisomy

The addition of a single extra chromosome to a diploid complement, represented by the chromosomal constitution $2n + 1$.

Turner Syndrome

A human sex-chromosome aneuploidy resulting in an $XO$ monosomic female ($4/10{,}000$ female births) who is typically sterile.

Klinefelter Syndrome

A human sex-chromosome condition in males characterized by an $XXY$ trisomy (or $XXYY$ / $XXXY$ tetrasomy) occurring at a frequency of $40/10{,}000$, frequently associated with infertility.

Down Syndrome

An autosomal aneuploidy caused by trisomy of chromosome 21 ($2n + 1$), occurring at a birth frequency of approximately $14.3/10{,}000$.

Gene Balance

The genetic principle stating that normal development and physiology require a $1:1$ relative proportion of genes and their products in the genome.

Gene-Dosage Effect

A change in an organism's phenotype caused by an abnormal number of wild-type alleles, as observed in aneuploidies and segment duplications.

Chromosomal Deletion

A structural mutation involving the loss of a chromosomal segment; can occur internally as an intercalary deletion or at the tip as a terminal deletion.

Cri-du-chat Syndrome

A genetic disorder characterized by a cat-like infant cry, caused by a terminal or interstitial deletion in the short arm of human chromosome 5.

Chromosomal Duplication

A structural aberration that results in the doubling of a specific chromosomal segment, classified into tandem, reverse tandem, or terminal tandem duplications.

Chromosomal Inversion

A chromosomal rearrangement in which a chromosome segment is excised, rotated $180^\circ$, and reintegrated into the same chromosome.

Pericentric Inversion

A chromosomal inversion in which the inverted segment spans both arms and includes the centromere.

Paracentric Inversion

A chromosomal inversion confined to a single chromosome arm that excludes the centromere.

Chromosomal Translocation

A structural change occurring when a segment detached from one chromosome is reattached to a different, nonhomologous chromosome, thereby altering linkage relationships.

Reciprocal Translocation

A mutual exchange of segments between two nonhomologous chromosomes, which results in a characteristic four-chromosome cross configuration (cruciform) during prophase I of meiosis in translocation heterozygotes.