Read the passage and answer the following questions:
Mendel published his work on inheritance of characters in 1865 but for several reasons, it remained unrecognised till 1900. Firstly, communication was not easy (as it is now) in those days and his work could not be widely publicised. Secondly, his concept of genes (or factors, in Mendel's words) as stable and discrete units that controlled the expression of traits and, of the pair of alleles which did not 'blend' with each other, was not accepted by his contemporaries as an explanation for the apparently continuous variation seen in nature. Thirdly, Mendel's approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time. Finally, though Mendel's work suggested that factors (genes) were discrete units, he could not provide any physical proof for the existence of factors or say what they were made of.
Given below are two statements:
Statement I: Due to advancements in microscopy, scientists discovered structures in the nucleus that appeared to double and divide just after each cell division.
Statement II: Chromosomes were given their name, meaning coloured bodies, because they were visualised by staining.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Statement I is false but Statement II is true
Around 1900, better microscopes allowed scientists to watch cell division closely. This led to the discovery of chromosomes in the nucleus. Their behaviour later helped explain Mendel’s laws.
Statement I: Due to advancements in microscopy, scientists discovered structures in the nucleus that appeared to double and divide just after each cell division. — False. The structures appeared to double and divide just before each cell division, not just after it. They must double first so that each new cell gets a full set.
Statement II: Chromosomes were given their name, meaning coloured bodies, because they were visualised by staining. — True. The word chromosome means coloured body. They got this name because they were seen by staining.
NCERT Extract:
Chromosomal Theory of Inheritance – “… In 1900, three Scientists (de Vries, Correns and von Tschermak) independently rediscovered Mendel’s results on the inheritance of characters. Also, by this time due to advancements in microscopy that were taking place, scientists were able to carefully observe cell division. This led to the discovery of structures in the nucleus that appeared to double and divide just before each cell division. These were called chromosomes (colored bodies, as they were visualised by staining).”