Question

Which of the following is an event which does not occur during anaphase-1?
A. Spindle fibres pull homologous chromosomes towards the opposite poles of the spindle
B. The homologous chromosomes break their connection and separate out into two haploid sets of dyads.
C. One such set is present at each end of the spindle.
D. The process of separation of chromosomes which take place is called disengagement.

Answer 1

Hint: Cell division is one of the most common processes taking place in the body of multicellular organisms. It is basically of two types, that is, Mitosis and Meiosis. These are multiphase processes.

Complete Answer
The above-mentioned cell division phase (Anaphase - 1) is a part of the mitotic cell division process. Mitosis is further divided into four phases: Prophase, Anaphase, metaphase, and Telophase. In Anaphase, each chromosome splits from centromere into two wings of chromatids. These chromatids start moving towards opposite poles through spindle fibres. This entire process is considered as the first stage of Anaphase. Whereas, when these chromatids move further through the elongated spindle fibres to reach the pole then it is counted as a second phase of Anaphase.
Let's study each option mentioned above to find the correct answer:
Statement of option A, is correct to consider segregation of homologous chromosomes into chromatids, as one of the events taking place in Anaphase I. Therefore, it is the incorrect answer to the question.
Similarly, option B and C are also correct statements as they rightly discuss the events of Anaphase I. Therefore, are incorrect answers to the question.
However, the fourth option considering the process of separation of chromosomes as disengagement is a wrong statement as disengagement is a process that ensures assignment of a single centrosome to each daughter cell.

Therefore, option D is the correct answer.

Note:
Mitosis is a six phased cell division process. This process begins with Interphase where chromatin fibre gets converted into chromosomes. It is followed by Prophase that involves formation of spindle fibres. After Prophase, comes metaphase that involves arrangement of chromosomes at the equator of spindle fibres which is later followed by Anaphase. At last, comes the Telophase in which chromatids convert back into chromatin fibres along with disappearance of the spindle fibres.