Diagram o a replicatit an condensed metaphase eukaryotic chromosome. (1) Chromatid – ane o the twa identical pairts o the chromosome efter S phase. (2) Centromere
– the pynt whaur the twa chromatids titch. (3) Short (p) airm. (4) Lang (q) airm.
A chromosome (frae auncient Greek: χρωμόσωμα, chromosoma, chroma means colour, soma means bouk) is a DNA molecule wi pairt or aw o the genetic material (genome) o an organism. Maist eukaryotic chromosomes include packaging proteins that, aidit bu chaperone proteins, bind to an condense the DNA molecule tae prevent it frae acomin an unmanageable tangle.
Chromosomes are normally veesible unner a licht microscope anly whan the cell is unnergaein the metaphase o cell diveesion. Afore this happens, ivery chromosome is copied ance (S phase), an the copy is jyned tae the oreeginal bi a centromere, resultin aither in an X-shapit structur (picturt tae the richt) if the centromere is locatit in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends. The original chromosome and the copy are now called sister chromatids. In metaphase the X-shape structur is cried a metaphase chromosome. In this heichly condensed form chromosomes are easiest tae distinguish an study. In ainimal cells, chromosomes reach thair heichest compaction level in anaphase in segregation.
Chromosomal recombination in meiosis an subsequent sexual reproduction play a seegneeficant role in genetic diversity. If thir structurs are manipulatit incorrectly, throu processes kent as chromosomal instability and translocation, the cell mey unnergae mitotic catastrophe an dee, or it mey unexpectitly evade apoptosis, leadin to the progression o cancer.
Some uise the term chromosome in a wider sense, tae refer tae the individualised portions o chromatin in cells, aither veesible or nae unner licht microscopy. Houiver, ithers uise the concept in a narraer sense, tae refer tae the individualised portions o chromatin in cell diveesion, veesible unner licht microscopy due tae heich condensation.