Question

A cell in mitotic prophase can be distinguished from a cell in meiotic prophase by?
a) Formation of tetrad in a meiotic cell
b) The terminalization of chiasmata in late prophase of mitosis
c) Zipping in early prophase of mitosis
d) Presence of only half as many chromosomes in meiotic cell

Answer 1

Hint: Mitosis is the equational division which results in genotypically similar \[2\] daughter cells while, Meiosis is reductional division which results in 4 non-similar haploid daughter cells. Mitosis is divided into \[4\] stages viz, Prophase, Metaphase, Anaphase, Telophase whereas Meiosis is itself divided into meiosis-I and meiosis-II. M-I has Prophase-I, Metaphase-I, Anaphase-I, Telophase-II and M-II has Prophase-II, Metaphase-II, Anaphase-II, Telophase-II. M-II and Mitosis are quite similar but the stages of M-I differ.

Complete answer:
A tetrad is formed during one of the stages of prophase-I of Meiosis-I. (Refer the note section).
Option (a) is correct.
The terminalization of chiasmata is a process that occurs in prophase of meiosis and not in mitosis.
So, option (b) is incorrect.
Zipping is a process when the homologous chromosome forms a synaptonemal complex in prophase-I and this process also does not occur in mitosis.
Hence, option (c) is incorrect.
The chromosome number is half in the resulting \[4\] daughter cells after meiosis. The chromosome number in a parent meiotic and mitotic cell do not differ.
Option (d) is incorrect.

So the correct answer is option (a).

Note:
Meiotic division has \[2\] prophase stages: Prophase-I of M-I and Prophase-II of M-II.
Prophase-I is divided into \[5\] smaller stages namely, leptotene, zygotene, pachytene, diplotene, diakinesis.
Leptotene: The chromatin material decondenses and chromosome material appears.
Zygotene: Pairing of homologous chromosomes (synapsis) occurs, and a bivalent dyad of synaptonemal complex is formed.
Pachytene: chromosome divides to form sister chromatid and a bivalent tetrad is formed. Crossing over occurs between the non-sister chromatids of homologous chromosomes by the action of recombinase enzyme and recombination nodules are formed.
Diplotene: The synaptonemal complex dissolves except at the place of crossing over, where a x-shaped structure, ‘chiasmata’ is formed.
Diakinesis: The terminalization of chiasmata occurs here, meiotic spindle is assembled and by the end the nuclear membrane and other organelles disappear.
Prophase-II of M-II is similar to the prophase stage of mitosis and is much simpler than prophase-I. Here, the chromosomes condense and the centrosome starts moving towards the opposite pole. And by the end, the nucleolus, nuclear membrane, Golgi bodies, endoplasmic reticulum disappears.