Types of Chromosomes

There are 46 chromosomes in every somatic cell of a human being. Among them, 22 pairs (44) is the pair of autosomes and 23 (XX or XY) is the sex chromosomes. In 1956, describe JH Tjio and Albert Levan a technique for preparation of chromosomes, known as culture techniques for blood or tissue. In this technique, blood cells or white blood cells are separated from small fragments of tissue from any part of the body grown in culture medium.

There are 46 chromosomes in every somatic cell of a human being.  Among them, 22 pairs (44) is the pair of autosomes and 23 (XX or XY) is the sex chromosomes.  In 1956, describe JH Tjio and Albert Levan a technique for preparation of chromosomes, known as culture techniques for blood or tissue.  In this technique, blood cells or white blood cells are separated from small fragments of tissue from any part of the body grown in culture medium.

Before cell division, the nucleus of somatic cells, the chromosomes in a cell are scattered and can not be observed.  An excerpt from the bottom of the bean (Vaal), Phaseolus, known as PHA, when added to the culture medium to initiate cell division in the WBC.  This medium was incubated at 370 ° C in an incubator for 3 days, after which it is removed from the incubator and Colchicine is added.  Colchicine inhibits cell division and therefore more than most cultures of cells are arrested in cell division.  The cells in the phases will be carried by a slide, stained with different dyes, and chromosome preparations are made this way.  Each of these cells clearly photographed and chromosome morphology, size, shape and location of the centromere study.  Each chromosome can be viewed as two separate lines of chromatids joined at centromere.

There are four types of chromosomes based on the location of the centromere.

1) GM: In this type of chromosome the centromere is produced in the center and the four chromatids of equal length.

2) submetacentric: In this type of chromosome the centromere is a bit far from the center and therefore chromatids on one side slightly longer than the other.

3) acrocentric: In this type of chromosome the centromere is located near one end of the two chromatids, chromatids to opposite side is very long.  A small round structure, connected by a very thin thread that is observed in the short side of the chromatids.  The small round structure that is part of the chromosomes are known as satellite.  son in the thin region is called as satellite nucleolar organizer.

4) telocentric: In this type of chromosome the centromere is located at one end of the chromatid and hence one arm.  These telocentric not seen in human cells.

Special types of chromosomes
Eukaryotic besi4es posSQssin3 the usual type of chromosomes in the cells in your body, they contain some unusual and special types of chromosomes in some cells or some special moments of their life cycle.  The particular type of eukaryotic chromosomes are:
A.  polytene chromosomes, the nucleus of cells in the salivary glands of larvae of Diptera, including Drosophila chromosomes have unusually long and wide, with 100 or 200 of the size of chromosomes during meiosis and mitosis of the same species.  This is particularly surprising because the salivary gland cells are not part of the gland is formed, but chromosomes are replicated several times (a process called endomitosis) and become exceptional oversized called polytene chromosomes or stranded (discovered by Balbiani (l881) and appointed by Koller).  The result of endomitosis in the production process by 2X chromosomes, where X indicates the number of multiplication cycle.

polytene chromosomes of salivary gland cells of D. melanogaster chromosomes contain 1000-2000, which is formed by cycles of nine or ten consecutive years of growth and its partners are required parallel between other.Further have polytene chromosomes alternately light and dark stripes along the length.  The dark bands can be compared with the chromomeres of a chromosome is simple disk-shaped structures that occupy the entire diameter of the chromosome.  Contains euchromatin.  The light or other groups are composed of fibrils and heterochromatin.

If the polytene chromosomes in the salivary glands of fly larvae were tested at various stages of development, it appears that certain areas (groups of bands) to expand or “puff”.  This change of location puffs that development can continue, which in specific locations that correlate with specific stages of development.  This indicates smoking temporary changes in gene activity and involves several processes, such as accumulation of acidic proteins that form DNA loop despiralization chromonemal Balbiani ring called the sides of the dark, the synthesis of mRNA (messenger RNA) and storage (accumulation) of newly synthesized mRNA around Balbiani  rings.

2.  brush chromosomes in diplotene of meiosis, yellow eggs rich in vertebrate species contain nuclei with a lamp brush chromosomes, the largest number of unusually large sizes.  Brush chromosomes (detected by Rückert in 1892) formed during the active synthesis of mRNA molecules for future use of eggs in the division where there is no synthesis of mRNA molecules can be through active participation of chromosomes in mitotic cell division.

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  1. omGas Says...

    On April 27, 2011 at 5:58 am


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