Kromozom

Kromozom, also called a chromosome, is a long DNA molecule with proteins that carries genetic information. In eukaryotes, kromozom are located in the cell nucleus and organized into chromatin; they are visible under the light microscope mainly during cell division. Prokaryotes have a single circular kromozom in the cytoplasm, and many bacteria also contain smaller DNA elements called plasmids.

Structure and replication: In eukaryotes, kromozom are linear and contain a centromere, telomeres, and origins of replication. DNA is wound around histone proteins to form nucleosomes and higher-order chromatin structures. Each kromozom is replicated prior to cell division, producing sister chromatids held together at the centromere.

Function and heredity: Chromosomes carry genes, the basic units of heredity. The set of kromozom in a cell constitutes its genome. They ensure the transmission of genetic information during mitosis and, in sexually reproducing organisms, meiosis, which also introduces genetic variation.

Types and karyotype: Autosomes are non-sex kromozom; sex kromozom determine biological sex (for example, X and Y in humans). The normal human karyotype contains 46 kromozom (22 autosome pairs and 1 pair of sex kromozom). Variation occurs across species, and chromosome number varies independently of organism complexity.

Clinical and evolutionary context: Chromosome structure can undergo rearrangements—deletions, duplications, inversions, translocations—that can cause disease. Aneuploidies (such as trisomy 21) arise from improper chromosome segregation. Evolutionarily, chromosomal changes contribute to diversity and speciation. Organellar genomes in mitochondria and chloroplasts also carry DNA separate from the nuclear kromozom.