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Read this article to get information on chromosomes, its number, shape, and size!
Number:
The number of chromosomes in a given species is usually constant containing diploid number of chromosomes in their somatic cells and haploid (gametic or reduced) number of chromosomes in their sex cells (sperms and ova).
The number of chromosomes is variable from one to several hundreds among different species.
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For example, in pinworms the number of haploid chromosome is 1, in Ascaris megalocephala it is 2, while in certain protozoans (Aggregata), there are more than 300 chromosomes; in Paramecium 30 to 40, in radiolarians as many as 1600, in Hydra vulgaris 32, Musca domestica 12, Rana esculenta 26, Columba livia 80, Oryctolagus cuniculus 44, Gorilla gorilla 48 and Homo sapiens (man) 46.
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The chromosome numbers are also helpful for taxonomy. In the angiosperms the most frequent haploid number is 12 and members of this group have a range from 3 to 16. Similarly, in fungi, haploid number ranges from 3 to 8. In primates this haploid number is from 16 to 30.
This haploid set of chromosomes present in the nucleus of gametes is generally called genome, while in a diploid cell there will be two genomes. The diploid cells are the somatic or body cells. The diploid cells get the diploid set of the chromosomes by the union of the haploid male and female gametes in the sexual reproduction.
Shape and Size:
Chromosomes are rod-like or thread-like thin, coiled, elastic and contractile structures, known as chromatin threads. This condition of chromosomes is found during the interphase (resting stage) of the cell. They range from 0.1 µ to about 30µ in length and from 0.2µ to 2µ in diameter.
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Among human chromosomes, the largest are about 0.6µ in diameter and 10µ long, while the shortest may be about 1µ spheres. They are most clearly visible during metaphase stage of cell division. In this stage they become thick and filamentous. Generally plants have larger chromosomes than animals.
Trillium spp. appears to possess the largest known chromosomes which measure 30µ in length at metaphase. Monocotyledon plants usually have larger chromosomes than the dicotyledons which contain greater number of chromosomes. Each chromosome bears a clear zone, the centromere (kinetocore), which divides the chromosome into two equal or unequal parts called the chromosome arms.
