Kromosomenes

Kromosomenes are the fundamental units of heredity, present in the cells of almost all organisms. They are long molecules of DNA packaged with proteins, and they carry the genes that determine inherited traits.

Most eukaryotic organisms have multiple linear chromosomes located in the cell nucleus. Each chromosome has features such as a centromere, which guides segregation during cell division, and telomeres, which protect chromosome ends. The DNA is wound around histone proteins to form chromatin.

Prokaryotes, by contrast, usually possess a single circular chromosome in the nucleoid area, and may harbor small DNA molecules called plasmids.

Chromosome number is characteristic of a species. Humans typically have 46 chromosomes (23 pairs): 22 pairs of autosomes and 1 pair of sex chromosomes (XX for most females, XY for most males).

Chromosomes are reproduced and passed to daughter cells during cell division. In mitosis, somatic cells produce two genetically identical diploid cells. In meiosis, germ cells produce haploid gametes with recombination and independent assortment.

Structural variations include deletions, duplications, inversions, and translocations. Aneuploidy—an abnormal number of chromosomes due to nondisjunction—can lead to conditions such as Down syndrome (trisomy 21), Turner syndrome (monosomy X), and Klinefelter syndrome (47, XXY).

Modern genetics uses techniques such as karyotyping, fluorescence in situ hybridization (FISH), and genomic sequencing to analyze chromosomes and detect abnormalities.