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.