Chromosome

<p>A chromosome is a <a href="/facts/Nuclear_organization/jf5CngSq">package</a> of <a href="/facts/DNA/nB89Iauz">DNA</a> containing part or all of the <a href="/facts/Genome/31Sm08JT">genetic material</a> of an <a href="/facts/Organism/j8JkL09u">organism</a>. In most chromosomes, the very long thin DNA fibers are coated with <a href="/facts/Nucleosome/HX5DR9bn">nucleosome</a>-forming packaging <a href="/facts/Protein/Jxmagu3E">proteins</a>; in <a href="/facts/Eukaryotic/SkwyPLMA">eukaryotic</a> cells, the most important of these proteins are the <a href="/facts/Histone/krb5VJfp">histones</a>. Aided by <a href="/facts/Chaperone_(protein)/2SAjcVnW">chaperone proteins</a>, the histones bind to and <a href="/facts/DNA_condensation/FxRztPyV">condense</a> the DNA molecule to maintain its integrity. These eukaryotic chromosomes display a complex <a href="/facts/Three-dimensional_space/KAqKWUbS">three-dimensional structure</a> that has a significant role in <a href="/facts/Transcriptional_regulation/UXekWdWb">transcriptional regulation</a>.
</p><p>Normally, chromosomes are visible under a <a href="/facts/Light_microscope/5700vcna">light microscope</a> only during the <a href="/facts/Metaphase/WMPlWk8s">metaphase</a> of <a href="/facts/Cell_division/n5MrunWj">cell division</a>, where all chromosomes are aligned in the center of the cell in their condensed form. Before this stage occurs, each chromosome is duplicated (<a href="/facts/S_phase/vplz8LTU">S phase</a>), and the two copies are joined by a <a href="/facts/Centromere/AWxF1ClY">centromere</a>—resulting in either an X-shaped structure if the centromere is located equatorially, or a two-armed structure if the centromere is located distally; the joined copies are called '<a href="/facts/Sister_chromatids/pqqWuKII">sister chromatids</a>'. During <a href="/facts/Metaphase/WMPlWk8s">metaphase</a>, the duplicated structure (called a 'metaphase chromosome') is highly condensed and thus easiest to distinguish and study. In animal cells, chromosomes reach their highest compaction level in <a href="/facts/Anaphase/mcGBl6Q5">anaphase</a> during <a href="/facts/Chromosome_segregation/wvIl1RoC">chromosome segregation</a>.
</p><p>Chromosomal <a href="/facts/Genetic_recombination/uocNH0m7">recombination</a> during <a href="/facts/Meiosis/Pj5Q6nGN">meiosis</a> and subsequent <a href="/facts/Sexual_reproduction/hmsXy53s">sexual reproduction</a> plays a crucial role in <a href="/facts/Genetic_diversity/GIymbUr8">genetic diversity</a>. If these structures are manipulated incorrectly, through processes known as <a href="/facts/Chromosomal_instability/edohx6Dk">chromosomal instability</a> and <a href="/facts/Chromosomal_translocation/MKEwqpQw">translocation</a>, the cell may undergo <a href="/facts/Mitotic_catastrophe/Lc4fcckM">mitotic catastrophe</a>. This will usually cause the cell to initiate <a href="/facts/Apoptosis/8dVzSm4y">apoptosis</a>, leading to its own <a href="/facts/Cell_death/UYCzvewT">death</a>, but the process is occasionally hampered by cell mutations that result in the progression of <a href="/facts/Cancer/PVW6n1D0">cancer</a>.
</p><p>The term 'chromosome' is sometimes used in a wider sense to refer to the individualized portions of <a href="/facts/Chromatin/ha0TJheJ">chromatin</a> in cells, which may or may not be visible under light microscopy. In a narrower sense, 'chromosome' can be used to refer to the individualized portions of chromatin during cell division, which are visible under light microscopy due to high condensation.
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Chromosome open-in-new

Chromosome