In 1956 Tijo and Levan first successfully counted human chromosomes. What is the reason it took so many years to do so?
A) Watson and Crick's structure of DNA was not done until 1953.
B) Chromosomes were piled up on top of one another in the nucleus.
C) Chromosomes were not distinguishable during interphase.
D) A method had not yet been devised to halt mitosis at metaphase.
E) Chromosomes were piled up on top of one another in the nucleus, chromosomes were not distinguishable during interphase, and a method had not yet been devised to halt mitosis at metaphase.

Question

Quizplus · Accepted Answer

There were multiple factors that made it difficult to count human chromosomes, including the fact that chromosomes were piled up on top of one another in the nucleus, they were not distinguishable during interphase, and a method had not yet been devised to halt mitosis at metaphase. It was not until the development of specific staining techniques and improved microscopy that Tijo and Levan were able to successfully count human chromosomes in 1956. The discovery of the structure of DNA by Watson and Crick in 1953 played a role in understanding how chromosomes were organized, but it was not the main reason it took so many years to count them.

In 1956 Tijo and Levan First Successfully Counted Human Chromosomes