Cytogenetics and Medical Genetics Lecture Notes

Comprehensive vocabulary flashcards covering cytogenetic techniques (Caryotype, FISH, ACPA), chromosomal structures, nomenclature, and ethical/legal considerations in genetic sequencing.

Chromatin

The genetic material found in the interphase nucleus, composed of DNA and associated proteins.

Chromosomes

Small rod-shaped structures formed by the compaction and spiralization of DNA during mitosis, visible via light microscopy.

Supragenic cytogenetics

A branch of genetics that studies chromosomal diseases, such as Trisomy 21.

Intragenic cytogenetics

A branch of genetics involving variations at the nucleotide level, typically requiring molecular biology techniques.

Resolution

The smallest genomic anomaly that a specific technique is capable of detecting.

Caryotype

A global study technique with a resolution of $5$ to $10\,Mb$ ($15$ to $20\,Mb$ per text) that allows observing approximately $1000$ genes at once.

FISH (Hybridation in situ en fluorescence)

A targeted, precise technique using fluorescent probes with a resolution of approximately $10$ to $100\,kb$.

ACPA (Analyse Chromosomique sur Puce à ADN)

Also known as CGH-array, it detects very small genomic anomalies, including intragenic ones, by comparing DNA signals.

Sequencing

The most precise genetic technique, with a resolution of a single base pair ($1\,pb$).

Constitutional cytogenetics

The study of the genetic makeup that constitutes an individual, examined either prenatally or postnatally.

Acquired cytogenetics

The study of genetic anomalies that are acquired during an individual's lifetime.

Dysmorphologies

Physical particularities or constant physical signs that vary from normal human alignment due to genomic anomalies.

Jérôme Lejeune

The scientist who, in 1959, demonstrated that Down Syndrome was associated with the presence of three copies of chromosome 21.

Chromosomal banding

The alternation of light and dark bands on chromosomes, which first appeared in 1970.

Centromere

The central structure that connects two chromatids of a metaphase chromosome.

Telomeres

The hexanucleotide repeat sequences at the ends of chromosomes that serve as a biological clock.

Metacentric

A chromosome classification where the short arm (p) and long arm (q) are of equal size.

Submetacentric

A chromosome classification where the short arm (p) is smaller than the long arm (q).

Acrocentric

Chromosomes ($13$, $14$, $15$, $21$, and $22$) with a very small short arm containing nucleoluas organizer genes.

Autosomes

The $22$ pairs of human chromosomes that are not sex chromosomes.

Gonosomes

The pair of sex chromosomes, which are XX in females and XY in males.

Amniocytes

Cells from the amniotic fluid used for prenatal caryotyping via amniocentesis.

Colchicine

A substance known as a mitotic spindle poison used to block cells in metaphase for chromosomal study.

R-bands

Chromosomal bands obtained by heat denaturation ($Heat$); the dark bands are rich in genes.

G-bands

Chromosomal bands obtained by trypsin treatment; the dark bands are poor in genes.

Euchromatin

The part of chromatin that is rich in genes.

Heterochromatin

The part of chromatin that is poor in genes and can vary in length without affecting the phenotype.

SRY gene

The gene located on the Y chromosome responsible for male differentiation.

Probe (Sonde)

A double-stranded DNA fragment labeled with a fluorochrome used in FISH to target specific complementary sequences.

Chromosomal painting

A FISH technique using probes that color an entire chromosome to identify structural rearrangements or extra segments.

Syndrome de Di George

A condition associated with a micro-deletion in the $22q11.2$ region of chromosome 22.

Subtelomeric probes

Probes targeting the gene-rich regions located just below the true telomeres, often used to detect translocations.

HCG (Hybridation Comparative Génomique)

Also known as CGH, a technique that compares signal intensities to detect DNA gains or losses but cannot identify balanced rearrangements.

Mosaicism

A condition where an individual has a clone of abnormal cells alongside normal cells due to a mitotic error after fertilization.

Variant of Significance Uncertain (VOUS)

A genetic variation (Class 3) where it is not yet certain if the variant is pathogenetic or benign.

High-throughput sequencing

A method of analyzing billions of bytes of data by fragmenting DNA, adding adaptors, and aligning sequences to a reference genome.

Exome

The entirety of the coding genes within the human genome.

Incidental data (Données incidentes)

Pathogenic variations discovered fortuitously during genetic analysis that are unrelated to the initial medical indication.

Secondary data (Données secondaires)

Factual results obtained by intentionally searching for anomalies in genes unrelated to the initial indication, a practice forbidden in France.