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(from ancient greek: χρωμόσωμα / chromosoma)
chroma means ‘color’
soma means ‘body’
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*a chromosome is a ‘DNA molecule’ with part (or all) of the genetic material (‘genome’) of an ‘organism’*
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(‘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’)
(the original chromosome and the copy are now called ‘sister chromatids’)
(during ‘metaphase’, when a chromosome is in its most condensed state, the X-shape structure is called a ‘metaphase chromosome’)
(in this ‘highly condensed form’, chromosomes are easiest to distinguish + study)
(‘chromosomes’ vary widely between different organisms)
(some species such as certain ‘bacteria’ (which lack ‘histones’) also contain ‘plasmids’ or other ‘extra-chromosomal DNA’)
(these are circular structures in the ‘cytoplasm’ that contain ‘cellular DNA’ and play a role in ‘horizontal gene transfer’)
(in prokaryotes (‘nucleoids’) + viruses, the DNA is often densely packed and organized; in the case of archaea, by homology to eukaryotic histones, and in the case of bacteria, by ‘histone-like proteins’)
(compaction of the duplicated chromosomes during cell division (mitosis or meiosis) results either in a four-arm structure (pictured to the right) if the centromere is located in the middle of the chromosome or a two-arm structure if the centromere is located near one of the ends)
(‘chromosomal recombination’ during ‘meiosis’ + subsequent ‘sexual reproduction’ play a significant role in ‘genetic diversity’)
(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’)
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(however, others use the concept in a narrower sense, to refer to the individualized portions of ‘chromatin’ during ‘cell division’, visible under ‘light microscopy’ due to high ‘condensation’)
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*🌈✨ *TABLE OF CONTENTS* ✨🌷*
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