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| Karyotype |
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| Chromosome number is a species-specific character. The complete set of chromosomes in the body cell of a species is known as karyotype. For example, the 23 pairs of chromosomes found in the somatic cells represent the human karyotype. In the karyotype it is possible to identify individual chromosomes based on the following characters: |
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| 1. Total length of the chromosomes |
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| 2. Ratio of the lengths of short and long arms of a chromatid |
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| 3. Position of the centromere (Primary constriction) |
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| 4. Position of the secondary constriction (nucleolar organiser) |
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| 5. Identification and estimation of euchromatin and heterochromatin |
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| This process of identification is called karyotyping. |
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| Following karyotyping, the homologous pairs of chromosomes can be arranged in a series of decreasing lengths. Such an arrangement is called as an idiogram or karyogram. In the idiogram, the chromosomes are arranged in a numerical sequence and classified into distinct groups. The human chromosomes for example, can be divided into 6 groups - A group containing the first three pairs, B group containing 4th and 5th pair, C group containing the 6th to 12th pair and X, D-group containing 13th, 14th and 15th pairs, E group containing 16th, 17th and 18th pair, F group containing 19th and 20th pair and G group containing 21st , 22nd pairs and Y chromosome of males. |
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| fig. 17.11- Human Karyotype [1-22 Autosomal Pairs] |
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