- They are the thread like structures that appear in the nucleus at the time of cell division and play an important role in the inheritance of a species.
- During cell division, the chromatin of the nucleus transforms into chromosomes by the process of condensation and contraction.
- Chromosomes show maximum contraction and condensation during metaphase of cell division and thus can easily be studied at this stage.
- A typical metaphase chromosome appears to be consisting of two arms and a primary constriction called centromere (kinetochore) between them.
- The two arms of the chromosome are called chromatids and the centromere is the region where the spindle fibers are attached during cell division.
- A chromosome having no centromere cannot participate in the cell division (anaphase).
- The position of the centromere on chromosome shows variation; hence we have different types of chromosomes.
- Chromosomes have been aptly described as the ‘vehicles of heredity’ as they carry the genes from one generation to the other.
- They undergo replication during cell division producing exact copies of them and are distributed equally in the daughter cells.
- In eukaryotes, the number, arrangement, and structure of chromosomes are specific for a particular species.
- In prokaryotes, which do not possess a well-organized cell nucleus, the chromosomes are freely distributed in the cytoplasm and are called Nucleoids are more or less simple structures when compared to the eukaryote chromosomes.
Somatic chromosome number of some organisms:
|Penicillium 2 (haploid)||Garden pea 14||Drosophila 8|
|Mucor 2||Onion 16||Mouse 40|
|Yeast 18||Rice 24||Man 46|
|Neurospora 7 (haploid)||Sugarcane 80||Mosquito 6|
- The major chemical components of the chromosome consist of DNA, RNA, proteins, and Lipids.
- In addition, polysaccharide and metal ions are also present in little quantities.
- The chromosomes of most organisms are composed of about 90% of “DNA-protein” (deoxyribonucleic protein) and 10% of “residual chromosome”. Of the 90% of DNA protein, 45% is DNA and the remaining 55% is histones and protamines (basic proteins).
Size of the Chromosomes
- The relative size of the chromosome usually differs from one organism to another.
- The length may vary from 0.2 µm and the diameter from 0.2µm to 3µm. In the case of human, the most common length ranges approximately between 4 µm to 6 µm.
- The giant chromosomes of insects and some other organisms may have a length of about 800 µm and a width of 10 µm.
Types of Chromosomes:
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Naeem Javid Muhammad Hassani is working as Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu (techurdu.net) Forestrypedia (forestrypedia.com), All Pak Notifications (allpaknotifications.com), Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.