chromosomy

Chromosomy (Polish for chromosomes) are long, thread-like structures in the nucleus that carry genetic information in the form of DNA. In eukaryotes, DNA is packaged with histone proteins into chromatin and organized into linear chromosomes. Prokaryotes typically have a single circular chromosome, plus smaller DNA molecules called plasmids.

Humans, somatic cells contain 46 chromosomes, arranged as 23 pairs: 22 autosomes and 1 pair of sex chromosomes. The two copies of each autosome are inherited from each parent. Sex chromosomes determine biological sex, with XX in typical females and XY in typical males, though variations exist.

During cell division, chromosomes condense to become visible under light microscopy. Sister chromatids are identical copies held at the centromere; they separate during mitosis to ensure each daughter cell receives a complete set. Meiosis reduces chromosome number by half, producing haploid gametes.

Chromosomes carry genes at specific locations, or loci. Variations in chromosome structure (deletions, duplications, inversions, translocations) or number (aneuploidy such as trisomy 21) can cause developmental disorders and disease. Detection methods include karyotyping, fluorescence in situ hybridization (FISH), and various molecular techniques.