Human chromosomes, Biology

HUMAN CHROMOSOMES

The normal diploid (2N) chromosome number in human being is 46.

It was given by T.H. Tjio and A. Levan in 1956.

The chromosome complement of a cell depicting the number, size and form of the chromosome as seen in metaphase of mitosis is called karyotype.

The chromosomes are morphologically numbered into 7 groups. (size and position of centromere) by Denver and Colorado (1960)

Group (A)            : 1-3 chromosomes of largest size and submetacentric or metacentric centromere.

Group (B)            : 4-5 chromosomes with less larger size, submetacentric

Group (C)            : 6-12 chromosomes with medium sized and submetacentric centromere.

Group (D)            : 13-15 chromosomes, shorter than group 'c' with centromere near the end (Arcocentric). They are sat chromosomes or satellite.

Group (E)            : 16-18 chromosomes, short sized, with median or submedian centromere.

Group (F)            : 19-20 chromosomes, short sized with median centromere.

Group (G)           : 21-22 chromosomes, smallest in size, Acrocentric and are also satellites.

X chromosome is placed in 'C' group due to its larger size and submedian centromere and Y-chromosome is placed in group 'G' due to its short size and terminal centromere.

Posted Date: 10/8/2012 3:27:26 AM | Location : United States







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