Prof. Dr. Sohan Raj Tater
The term chromosome refers to the deeply staining DNA containing filamentous bodies observed in the dividing cells of nucleate organisms. The chromosomes are nuclear components possessing special organic individuality and functions. They bear genes or hereditary units and are capable of reproducing themselves without involving any change in morphology and physiology at successive generations. The chromosomes can be reality stained with basic dyes. Such as basic fuchsin (fuelgen's stain) carmine, haematoxyline, crystal violet etc.
The chromosomes are filamentous bodies found in the nucleus and are visible during cell division. They are linkage structures each consisting of a linear sequence of genetic information or genes. The chromosomes of prokaryotes and eukaryotes are essentially similar in two main activities:
- They are concerned with transmission of genetic information from cell to cell and generation to generation.
- They are concerned with the ordered release of genetic information to control cellular functions and developments.
They are auto duplicating structures of differential complexity in eukaryorates and prokaryotes and their morphology and organization are organism specific. The chromosomes of prokaryotes are generally double stranded circular DNA molecules but in some virus they may be single stranded. In eukaryotes they present a complex structure. Most of the chromosomes in a cell are called autosomes which carry genes for most of the body characters.
Besides there may be one, two or more chromosomes which carry genes for determination of sex as well as for sex linked character. They are called sex chromosomes (as for example X chromosome and Y chromosome). The standards chromosomes forming the chromosome complement of a cell are called A. In some species one or more extra chromosomes are present in addition to A chromosomes. They are called B chromosomes or super numerary chromosomes or accessory chromosomes.[136]
Doctoral Thesis, JVBU