Cytogenetics: Chromosome Structure and Classification

Comprehensive vocabulary flashcards covering chromosome structure, classification groups A-G, ploidy abnormalities, and various chromosomal banding techniques.

Chromosome

Threadlike, colored bodies that contain genes.

Centromere

Structure found in the middle of a chromosome used during cell division as an attachment point.

Telomere

Located at both ends of a chromosome; used to maintain chromosomal integrity by capping off the ends.

p

The short arm of a chromosome.

q

The long arm of a chromosome.

Kinetochore

A protein complex that assembles before cell division where spindle fibers attach.

Autosomes

The $22$ pairs of chromosomes ($1-22$) that control general body traits.

Sex chromosomes

The $23rd$ pair ($X$ and $Y$) that decides if an organism develops as a male or a female.

Metacentric

Chromosomes where the two arms are roughly equal in length and the centromere is at the middle.

Submetacentric

Chromosomes with short and long arms of unequal length with the centromere more towards one end.

Acrocentric

Chromosomes where the centromere is very near to one end, resulting in a very small short arm.

Telocentric

Chromosomes where the centromere is located at the terminal end; these do not exist in humans.

SAT Chromosomes

Short for Sine Acido Thymonucleinico; chromosomes that contain a satellite, which are the acrocentric chromosomes.

Stalk/Satellite

An antenna-like structure of some chromosomes containing genes that code for rRNA and responsible for nucleolus formation.

Secondary Constriction

The structure that holds the stalk or satellite.

Karyotyping

The process of extracting nuclei-containing cells, initiating cell division until metaphase, and arranging chromosomes by group and size.

Karyogram

The result of grouping and arranging chromosomes based on centromere location and size.

Group A

Comprised of chromosomes $1-3$; they are the largest chromosomes.

Group B

Comprised of chromosomes $4-5$; large submetacentric chromosomes with two arms very different in size.

Group C

Comprised of chromosomes $6-12$ and the $X$ chromosome; medium-sized submetacentric chromosomes.

Group D

Comprised of chromosomes $13-15$; medium-sized acrocentric chromosomes with satellites.

Group E

Comprised of chromosomes $16-18$; small chromosomes where $16$ is metacentric and $17-18$ are submetacentric.

Group F

Comprised of chromosomes $19-20$; small metacentric chromosomes.

Group G

Comprised of chromosomes $21-22$ and the $Y$ chromosome; small acrocentric chromosomes.

Euploidy

The condition of having a normal number of structurally normal chromosomes.

Aneuploidy

Any abnormal number of chromosomes that is not a multiple of the haploid number of $23$.

Nondisjunction

The failure of chromosomes to separate normally during cell division (meiosis).

Trisomy

The presence of an extra chromosome, such as Trisomy $21$.

Monosomy

The absence of a single chromosome, such as Turner syndrome.

Polyploidy

Chromosome number higher than $46$ that is an exact multiple of the haploid number ($23$), such as triploidy ($3n$) or tetraploidy ($4n$).

Chromosomal Banding

A staining technique producing alternating light and dark stripes (bands) used to identify genetic loci and morphologic abnormalities.

Euchromatin

Lightly packed chromatin enriched in genes and active in transcription.

Heterochromatin

Tightly packed chromatin with low gene density and deacylated histone tails where genes are typically silenced.

Constitutive heterochromatin

Stable and permanent heterochromatin found at the same regions (e.g., centromeres) in all cells; contains repetitive satellite DNA.

Facultative heterochromatin

Reversible heterochromatin that can switch between inactive and active states; associated with development and differentiation.

G-banding

Uses Giemsa stain where dark bands represent $A-T$ rich regions and light bands represent $G-C$ rich regions.

R-banding

The reverse pattern of G-banding using Giemsa dye; dark bands are $G-C$ rich and light bands are $A-T$ rich.

Q-banding

Uses fluorescent Quinacrine stain; dark bands are $A-T$ rich and light bands are $G-C$ rich.

C-banding

Staining technique used to identify constitutive heterochromatin, specifically at centromeric regions.

T-banding

Staining technique used for telomeric regions using Giemsa stain or Acridine orange.

NOR Staining

A silver staining method that identifies Nucleolar Organizing Regions and stains stalks/satellites on acrocentric chromosomes.