Clinical Cytogenetics and Chromosomal Abnormalities

Comprehensive vocabulary flashcards covering clinical cytogenetics, chromosomal banding techniques, and major numerical and structural anomalies.

Clinical Cytogenetics

The study of the structure and number of chromosomes using light microscopy, specifically during mitosis when chromatin is compact and visible.

Philadelphia chromosome

A small chromosome discovered in 1960 in patients with chronic myeloid leukemia, providing the first proof that cancer has a genetic cause in somatic cells.

Metacentric chromosomes

Chromosomes where the centromere is positioned in the middle, resulting in arms of equal length.

Submetacentric chromosomes

Chromosomes where the centromere is slightly displaced, resulting in one arm being shorter than the other.

Acrocentric chromosomes

Chromosomes where the centromere is very close to one end, resulting in one very short arm and one very long arm.

G-banding

A technique using trypsin followed by Giemsa staining that highlights dark bands rich in AT bases, associated with heterochromatin.

Q-banding

A technique using quinacrine, a fluorescent dye that produces brighter fluorescence in regions rich in AT bases.

R-banding

Reverse banding obtained through heat denaturation, highlighting GC-rich regions (euchromatin) that are transcriptionally active.

Cariogram

The representation of the chromosomal asset as a series of banded chromosomes.

Karyotype

The complete set of chromosomes of an individual, described by number, shape, and dimensions (e.g., $46, XX$ or $46, XY$).

Ideogram

Specific schematic diagrams for each chromosome showing the bands based on their resolution.

Mosaicism

The presence of different cell populations with different chromosomal assets in the same individual, resulting from acquired anomalies after zygote formation.

Limit of resolution

The threshold below which traditional cytogenetics cannot identify chromosomal anomalies, defined as $5-10\,Mb$.

Balanced structural anomalies

Chromosomal reorganizations (like inversions or translocations) that do not result in a net gain or loss of genetic material and usually do not cause an abnormal phenotype.

Unbalanced structural anomalies

Chromosomal alterations (like deletions or duplications) that result in a loss or gain of genetic material, often linked to malformations and intellectual disability.

Triploidy

A polyploidy condition where cells possess three complete sets of chromosomes, totaling $69$ chromosomes ($3n$).

Tetraploidy

A condition where cells possess four complete sets of chromosomes, totaling $92$ chromosomes ($4n$).

Non-disjunction

The failure of chromosomes or chromatids to separate during meiosis or mitosis, representing the main cause of aneuploidies.

Anaphase lag

A delay in chromosome migration during cell division that leads to the loss of a chromosome, potentially causing mosaicism if it occurs after fertilization.

Trisomy 21

Also known as Down syndrome, characterized by a karyotype of $47, XX+21$; its incidence is roughly $1$ in $850$ live births.

Trisomy 18

Known as Edwards syndrome, a severe chromosomal condition with an incidence of approximately $1$ in $6000$ live births.

Trisomy 13

Known as Patau syndrome, a severe condition with an incidence of $1$ in $10,000$ live births, often involving Robertsonian translocations.

Trisomy parziale (Partial trisomy)

A condition where only a duplicated segment of a chromosome is present rather than an entire extra chromosome.

Trisomia libera (Free trisomy)

A condition where the extra chromosome is complete and exists as an autonomous element in the karyotype.

Sindrome di Turner

The only monosomy compatible with life ($45,X$), characterized by a female phenotype with signs like amenorrhea and lack of secondary sexual characteristics.

Sindrome di Klinefelter

A male chromosomal anomaly ($47,XXY$) often diagnosed in adulthood due to infertility and characterized by small testicles and reduced testosterone.

Sindrome di Jacobs

A condition in males with the karyotype $47,XYY$, where individuals are often taller than average but have normal fertility.

Iceberg chart

A graphical representation showing that the observable chromosomal anomalies are only a small portion of the total, as many result in very early unrecognized pregnancy loss.