Kromosoomi

Kromosoomi (Estonian for chromosomes) are long, thread-like structures inside cells that carry genetic information in the form of DNA. In most organisms they reside in the cell nucleus as part of chromatin, a complex of DNA and proteins that condenses during cell division. A kromosoom typically consists of a DNA molecule and associated proteins; during replication, its DNA is copied to form sister chromatids that are held together at the centromere. The ends of a kromosoom are protected by telomeres.

Within humans, somatic cells contain 46 kromosoomi arranged as 23 pairs: 22 autosome pairs and 1 pair of sex chromosomes (XX in most females, XY in most males). The study of kromosoom number and structure, through karyotyping or other methods, is called cytogenetics. Kromosoomid are classified as autosomes or sex chromosomes; some species have different numbers. In prokaryotes, a single circular chromosome is typical, and eukaryotic organelles such as mitochondria and chloroplasts have their own small circular kromosoomi.

During cell division, kromosoomi ensure accurate inheritance. In mitosis, a complete set is replicated and evenly distributed to two daughter cells. In meiosis, chromosome pairing and recombination generate haploid gametes and genetic variation.

Abnormal kromosoomi number or structure can lead to disorders. Examples include aneuploidies such as trisomy 21 (Down syndrome), trisomy 18 (Edwards syndrome), trisomy 13 (Patau syndrome), and sex-chromosome conditions such as Turner syndrome (monosomy X) and Klinefelter syndrome (XXY).

Kromosoomi are studied using cytogenetic techniques such as karyotyping and fluorescence in situ hybridization (FISH), as well as DNA sequencing and genomic analyses. The concept remains fundamental to genetics, development, evolution, and medicine.