Question

As per the Denver Convention, the autosomes of man have been classified in _______ groups
A. 7
B. 4
C. 3
D. 16

Answer 1

Hint: A chromosome is a thread-like structure packed with DNA molecules and proteins. Cytogenetics involves the study of chromosomes during cell division. They use methods such as karyotyping to observe the chromosome structure and number. It also enables us to detect abnormality in the chromosomes. Nowadays, for more accurate results techniques such as fluorescent in situ hybridization are used.

Complete answer:
Humans 46 chromosomes i.e. 23 pairs. Out of the 23 pairs, 22 are autosomes (chromosomes that are not sex chromosomes).
After DNA replication a chromosome has formed a sister chromatid (identical) joined at the centromere. A typical chromosome structure consists of two arms and a centromere. Centromere helps form spindle fibers during cell division.
At the beginning to examine the human karyotype, on a slide, the heat fixed cells stained with Giemsa were squashed and placed under a microscope. They used distilled water on the slide making the cells turgid and difficult to observe. This was the reason why initially it was believed that humans had 48 chromosomes. In 1952, accidentally a technician T.C. Hsu used saline instead of water before the cells were squashed after staining. The solution being hypotonic ensured that the cells got swollen and it burst open. The chromosomes were no longer stuck together but visible.
Denver classification is an old system of classification. It was given in 1959 at a conference of genetics at Denver. The human chromosomes were placed in different groups depending on the size of the chromosome. According to this system, chromosomes were grouped into 7 types. Sex chromosomes were also a part of this grouping. The chromosomes in order of their decreasing length were placed in different groups. This was done way before it was possible to identify the centromeres of the chromosomes. Modern classification is based on the position of the centromere.

Therefore the correct option is (A). As per the Denver convention, the autosomes were classified into 7 groups.

Note: Klaus Patau modified the Denver system of classification, according to which the human chromosomes were grouped based on the position of the centromere and the size of the chromosome. Just like the Denver classification, the groups were seven (A, B, C, D, E, F, and G). C and G contained the sex chromosomes, along with autosomes, X and Y respectively. Group A and F have Metacentric chromosomes (centromere is in the middle of the chromosome and the two arms are equal in length). Group D and G are Acrocentric (centromere is near one end, one arm is long while the other is short). All the other groups are Subcentric (the centromere is not exactly in the middle of the chromosome).