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In a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity.
Bacterial chromosomes tend to be tethered to the plasma membrane of the bacteria.If these structures are manipulated incorrectly, through processes known as chromosomal instability and translocation, the cell may undergo mitotic catastrophe and die, or it may unexpectedly evade apoptosis, leading to the progression of cancer.Some use the term chromosome in a wider sense, to refer to the individualized portions of chromatin in cells, either visible or not under light microscopy.The author has been particularly disappointed by the illogicality of the present chromosomal (chromatin-chromosome) terminology based on, or inferred by, two terms, Chromatin (Flemming 1880) and Chromosom (Waldeyer 1888), both inappropriately ascribed to a basically non coloured state.referring to the term chromatin, which was introduced by Walther Flemming.(2) Centromere – the point where the two chromatids touch. Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division.
Before this happens, every chromosome is copied once (S phase), and the copy is joined to the original by a centromere, resulting in an X-shaped structure.
In molecular biology application, this allows for its isolation from plasmid DNA by centrifugation of lysed bacteria and pelleting of the membranes (and the attached DNA).
Prokaryotic chromosomes and plasmids are, like eukaryotic DNA, generally supercoiled.
Diagram of a replicated and condensed metaphase eukaryotic chromosome.
(1) Chromatid – one of the two identical parts of the chromosome after S phase. A chromosome (from ancient Greek: χρωμόσωμα, chromosoma, chroma means color, soma means body) is a DNA molecule (wrapped around Histone Protein in Eukaryotes) with part or all of the genetic material (genome) of an organism.
Aided by the rediscovery at the start of the 1900s of Gregor Mendel's earlier work, Boveri was able to point out the connection between the rules of inheritance and the behaviour of the chromosomes.