Question

The thick thread stage occurs in:
A. Leptotene
B. Zygotene
C. Pachytene
D. Diplotene

Answer 1

Hint: Thick thread stage is one of the phases of chromosomes during the process of cell division. Cell division is the process by which a cell divides into two or four daughter cells. There are two major types of cell division named mitosis and meiosis. Mitosis is referred to as equational division and meiosis is referred to as reductional division.

Complete answer:
Meiosis as evident is a pretty complex type of cell division. Meiosis is usually associated with spore formation when concerned with plants and with gamete formation when talking about animals. It is referred to as reductional division because after the division the daughter cells possess only half the chromosomal set of the parent cell genome. It occurs only in specialized diploid cells. It involves chromosomal duplication once but the cell division occurs twice. In the Leptotene stage, the chromosomes are long and thin whereas in zygotene the start pairing results in synapse formation, as a result, the chromosomes at this stage are referred to as bivalent. In the Pachytene stage, the chromosomes appear like thick thread, and crossing over along with an exchange of genetic fragments between non-sister chromatids takes place whereas in diplotene the homologs start moving away from each other towards opposite poles.
Hence, the correct answer for the above question is option (C)-Pachytene.

Note: In the pachytene stage, both the homologous chromosomes display two chromatids so that the bivalent of the zygotene stage now appears to be composed of four chromatids, known as a tetrad. Pachytene stage is the component of Prophase-I of meiosis.