hromosom

A hromosom is a long, thread-like structure that carries genetic information. In most eukaryotes, hromosoomid are linear DNA molecules packaged with histone proteins and reside in the cell nucleus. Prokaryotes possess circular chromosomes in the cytoplasm, typically lacking histones in the same way as eukaryotes, though some archaea use histone-like proteins.

A hromosom includes a centromere, telomeres at its ends, and a series of genes distributed along the DNA. DNA is organized into nucleosomes—DNA wrapped around histone octamers—and further folded into higher-order chromatin, enabling compact packaging within the nucleus. The ends (telomeres) protect chromosome ends from deterioration.

Chromosome number and structure vary among species. In humans, somatic cells contain 46 hromosoomid arranged in 23 pairs (22 autosomes plus 1 pair of sex chromosomes, XX or XY). Gametes carry 23 hromosoomid and combine during fertilization to form a 46-chromosome embryo. Chromosomes exist as homologous pairs except in haploid gametes.

Genome duplication and distribution: During the S phase of the cell cycle, hromosoomid are replicated to form sister chromatids. In mitosis, sister chromatids separate into two daughter cells. In meiosis, homologous chromosomes pair, exchange genetic material (crossing over), and are reduced to haploid gametes, increasing genetic diversity.

Clinical and research relevance: Chromosome analysis through karyotyping, fluorescence in situ hybridization (FISH), and sequencing detects structural variations such as deletions, duplications, inversions, and translocations, as well as aneuploidies. These findings underpin understanding of developmental disorders and cancers; for example, trisomy 21 causes Down syndrome.