Question

The stage during which separation of the paired homologous chromosomes begins:
A) Diakinesis
B) Pachytene
C) Zygotene
D) Diplotene

Answer 1

Hint: Pairing of homologous chromosome and its Separation occurs in prophase I of meiosis.

Complete answer:
Meiosis has two successive divisions (meiosis I and meiosis II) and short interphase present in between them in which genetic material gets duplicated.
Meiosis I have a comparatively long prophase than the mitotic division.
It is divided into five stages:
1) Leptotene: in this stage chromosomes appear to have long thin thread-like structure and hence are named leptotene (means thin thread).
All chromosomes are oriented toward centrioles giving it the look of a bouquet and hence it is also called the bouquet stage.
2) Zygotene: In this pairing of homologous chromosomes occurs. Each pair of homologous chromosomes is called bivalent (hence, bivalents are formed in zygotene).
Synaptonemal complex forms in between the homologous chromosomes which control the pairing of them.
3) Pachytene: The exchange of genetic material between non-sister chromatids of homologous chromosomes occurs in this stage. This is called crossing-over.
Crossing over leads to the recombination of genes.
4) Diplotene: Repulsion between homologous chromosomes begins due to the dissolution of the synaptonemal complex.
5) Diakinesis: this is the last stage of prophase I, which is characterized by terminalisation of chiasmata.
At the end of this stage, the Nuclear membrane and nucleolus disappear.
So the correct answer is option C.

Note: Besides mitosis and meiosis, there are two more types of cell division:
1) Amitosis: It means a direct division of cells without the appearance of a chromosome or without spindle formation. Example: fission in bacteria.
2) Endomitosis: in this chromosome doubling is not followed by cell plate formation. This happens when the cell is treated with colchicine. It is a chemical that stops the spindle fiber formation and induces polyploidy.