Question

Diplotene stage of prophase-I is characterized by
A. Dissolution of the synaptonemal complex
B. Separation of synapsed homologous chromosomes except for the sites of crossover.
C. Formation of X-shape structures called chiasmata.
D. All of these.

Answer 1

Hint: The process of cell division where a single cell forms four daughter cells is known as meiosis. There are two stages to meiosis, Meiosis-I, and Meiosis-II. There are various stages to Meiosis and all the phases have distinctive features. Prophase-I is the first phase of Meiosis-I. Prophase-I has several sub-phases, Leptotene, Zygotene, Pachytene, DIplotene, and Diakinesis.

Complete answer:
Meiosis is the reductional division which consists of two stages-
Meiosis-I consist of
-Prophase- The chromosomes undergo condensation and simultaneous pairing. They position themselves along with their homologous partners for forming chiasmata by overlapping the ends of each sister chromatid. This process is known as crossing over. All these occur in several sub-phases,
Leptotene, Zygotene, Pachytene, DIplotene, and Diakinesis.
-Metaphase-The homologous pair of chromosomes align up at the equator attached to the spindle fibres.
-Anaphase-The spindle fibres contract and pull the chromosomes apart from each other towards the equator.
-Telophase- The separated chromosomes at the poles start decondensing and forming the nucleus and nuclear membrane. The cell is separated into two daughter cells by the formation of a cell furrow but this furrow only proceeds halfway through.
-Diplotene is a sub-phase of Prophase- I. During diplotene the synaptonemal complex undergoes dissolution. Therefore, option (a) is the correct answer.
The synapsed homologous chromosomes separate at the site of crossing over. Therefore, this option is also correct.
The homologous pair of chromosomes results in the formation of an X structure known as chiasmata. Therefore, this option is also correct.

Hence, the correct answer is option (D).

Note: In Meiosis, the first stage of Meiosis does not separate the cell completely but only narrow furrowing occurs. This furrowing is completed after the Meiosis-II when the four daughter cells are formed. In the first round only the maternal and paternal chromosomes undergo separation, but in meiosis-II, the sister chromatids also undergo separation.