Question

Refer to the following statements describing Prophase I of meiosis and answer the question.
(i) Thin thread-like chromosomes with a beaded appearance
(ii) Appearance of recombination nodules
(iii) Formation of bivalents/tetrads
(iv) Terminalisation of chiasmata
(v) Appearance of chiasmata
Identify the different stages with respect to the above-given features and select the correct option
A. (i) - Leptotene, (ii) -zygotene, (iii) -pachytene, (iv) - Diplotene, (v)- Diakinesis.
B. (i) - Leptotene, (ii) - zygotene , (iii) - pachytene, (iv) - Diakinesis , (v) - Diplotene.
C. (i) - Leptotene, (ii) - Pachytene , (iii) - Zygotene, (iv) - Diakinesis , (v) - Diplotene.
D. (i) - Leptotene, (ii) - Pachytene , (iii) - Diplotene, (iv) - zygotene , (v) - Diakinesis

Answer 1

Hint: A cell needs to undergo many processes to differentiate itself. Mitosis and meiosis are the important cycles occurring in our system, they divide the cells in different manners so as to basically condense the whole genome we got from our parents.

Complete answer:
Prophase is known to be the longest phase in karyokinesis. Prophase in meiosis is divided into 5 phases- Leptotene, pachytene, zygotene, diakinesis and diplotene.
All the phases have their speciality to form and many important events occur during these phases.
(i) Thin thread-like chromosomes with a beaded appearance- Leptotene is the stage when the sister chromatids can be distinguished from each other. They appear like thread structures. They are not distinct but look like a mass of entangled threads.
(ii) Appearance of recombination nodules- It is a long phase in which synapsis is done priorly. In this the exchange of chromosomes takes place, thus the appearance of recombination nodules is visible now. In this the shortening and thickening of chromosomes take place.
(iii) Formation of bivalents/tetrads- It is a sub-stage where synapsis occurs. It is the second stage. Condensation of chromosomes occurs here to form tetrads.
(iv) Terminalisation of chiasmata- It is the final step in prophase 1. In this, there is the termination of condensing of chromosomes. The nucleolus and nuclear envelope disappear. The chiasmata are seen clearly.
(v) Appearance of chiasmata- The stage where the synaptonemal complexes loosen and the chromatids are held at the chiasmata. Formation of chiasmata is visible here.

So the answer is option C: (i) - Leptotene, (ii) - Pachytene, (iii) - Zygotene, (iv) - Diakinesis , (v) Diplotene.

Note: Cell spends 14% of its time in prophase so making it the longest phase. In this, the nuclear membrane and microtubules have to be attached to the chromosomes. It is the first step in meiosis. The chromosomes are seen to be condensed and shortened in this phase.