Question

The genetically active area of the chromosome is
A. Euchromatin
B. Heterochromatin
C. Hapten
D. Cistron

Answer 1

Hint: Chromosome, the term comes from the Greek words ‘chroma’ is the colour and ‘soma’ is the body. Chromosomes are filamentous bodies found within the nucleus. They possess the ability of self-replication and play a crucial role in variation, mutation, heredity and evolution of organisms. The active area on the chromosome is lightly packed.

Complete answer: Chromosomes that are genetically and morphologically identical are known as homologous chromosomes. The number of chromosomes varies from species to species, however, their number remains constant within the same species.
Structure of the chromosome:
The shape of chromosomes varies from phase to phase during cell division, however, it is the metaphase chromosome that is brought understudy when the structure is concerned. It consists of two identical halves called sister chromatids. The chromatids are further made up of smaller units or sub-chromatids called chromonemata (singular- chromonema). The two sister chromatids are held together at a point called the centromere. Euchromatin is a form of chromatin that is less compact or lightly packed. It consists of a large amount of DNA or genes. Heterochromatin, on the other hand, is a rather tightly packed form of chromatin that consists of very less amount of DNA or genes.
a) Haptens are small molecules like carbohydrates, fats or nucleic acids that can act as an antigen and elicit an immune response only when they are in combination with proteins.
b)A cistron is the segment of the DNA that consists of information for the synthesis of a particular RNA or protein. Since Euchromatin contains more genes and is lightly packed, It becomes an easier format for gathering genetic information so that it can be transcribed which makes it genetically more active as compared to heterochromatin.
Hence, the correct answer is option A.

Note: Chromosomes are visible only during cell division. Depending upon the number of sets of chromosomes, an individual can be haploid (one set), diploid (two sets), triploid (three sets), etc. When there is a presence of a whole set of chromosomes, it is called euploidy. Euchromatin is lightly packed and has a large number of genes, whereas heterochromatin is a tightly packed form of chromatin that has less amount of DNA.