litninga

Litningar, or chromosomes, are long, thread-like structures located in the nuclei of eukaryotic cells that carry genetic information in the form of DNA and associated proteins. They are the fundamental units of heredity and are organized in a way that allows the accurate transmission of genetic material during cell division.

In humans, somatic cells contain 46 litningar arranged as 23 pairs: 22 autosomal litningar and one pair of sex litningar (XX in most females and XY in most males). Gametes carry a haploid set of 23 litningar. Each litning comprises a single, long DNA molecule wrapped around histone proteins and further compacted during division. After DNA replication, each litning consists of two sister chromatids held together at the centromere and separated during mitosis or meiosis to ensure equal distribution to daughter cells.

Key structural features include the centromere, which constrains the two chromatids together and forms the characteristic shape of a litning; telomeres at the ends of the litnings that protect against degradation; and the p and q arms, which describe the shorter and longer segments of the litning, respectively. The banding patterns created by staining help identify specific litningar and chromosomal regions.

Litningar house genes at defined loci, and their organization influences gene expression and inheritance. Variations in number or structure—aneuploidy, deletions, duplications, or translocations—can lead to developmental disorders and diseases. Common examples include trisomy 21 (Down syndrome) and sex-chromosome abnormalities such as Turner syndrome (monosomy X) or Klinefelter syndrome (XXY). Modern diagnostic techniques, including karyotyping, fluorescence in situ hybridization (FISH), and array comparative genomic hybridization (array CGH), detect chromosomal abnormalities to inform medical care.