Question

When the prophase chromosome is stained with acetocarmine, they take differential staining. This phenomenon is called as
(a)Idiogram
(B)Karyotype
(c)Heteropycnosis
(d)Satellite

Answer 1

Hint: It is a phenomenon shown by chromosomes in which certain regions of chromosomes stain more intensely than others. The quality or state of some chromosomes or parts of some chromosomes in a nucleus is more tightly coiled and takes up more stain or less tightly coiled than is usual that takes up less stain.

Complete answer:
Certain regions of chromosomes are stained by a phenomenon in the chromosomes which more intensely than others is called heteropycnosis. Heitz (1928) described that in a chromosome the regions that exhibit heteropycnosis may be composed of heterochromatin and called heterochromatic parts against the other parts that never show heteropycnosis and are called euchromatic parts. The chromosome in the non-condensed state was called euchromatin. In the chromosome, the heterochromatin part is closely associated with the nucleolus, so when the prophase chromosome is stained with acetocarmine they take differential staining due to the presence of heterochromatin and euchromatin regions, and this whole phenomenon is known as heteropycnosis. There are two different types of heteropycnosis: positive and negative heteropycnosis. The term heteropycnosis came from a Greek word (“hetero” means different or multiple and “pyknosis” means staining).

Positive heteropycnosis can be defined as when heterochromatic regions in a chromosome may be thicker and more dark-staining than the euchromatic ones where they were synthesized more nucleic acid and possibly more protein as well. When a chromosome is positively heteropycnotic in a prophase nucleus, it looks like a metaphase chromosome.

Negative heteropycnosis can be defined as when heterochromatic regions in a chromosome may appear thinner and stain more weakly than euchromatic regions in the same nucleus. These types of chromosomes usually have a fuzzy outline and at metaphase and still, look like prophase chromosomes.

Additional Information: 1) The heterochromatin and euchromatin in a chromosome are two major categories of chromatin higher-order structure, where heterochromatin has a condensed chromatin structure and is inactive for transcription, while euchromatin has a loose chromatin structure and active for transcription.
2) chromocenters in heterochromatin are defined by Heitz in 1928 as those regions of the chromosome that remain condensed during interphase and early prophase.
3) The metabolism of the chromosome is controlled by the heterochromatin, biosynthesis of the nucleic acids, and energy metabolism, which is usually located near the centromere (kinetochore), nucleolus organizer, and the ends of chromosomes, but are not restricted to these locations.
4) The DNA remains tightly packed in 20 to 30 nm fiber in heterochromatin which probably represents the configuration of transcriptionally inactive chromatin.
So, the correct answer is, ‘heteropycnosis’.

Note: In the same chromosomes, we can find both types of heteropycnosis that occur during different stages of cell division. E.g: We can take the example of a short-horned grasshopper, in which X-chromosome passes through a regular cycle in the course of spermatogenesis, being negatively heteropycnotic during the early spermatogonial divisions (at least during prophase and metaphase), and in the later spermatogonial divisions it is non-heteropycnotic (i.e., behaving like euchromatin) while positively heteropycnotic during prophase of meiosis.