Question

Pick out the item which has sequential arrangements.
a) Zygotene → Leptotene → Pachytene → Diplotene → Diakinesis.
b) Diakinesis → Zygotene → Leptotene → Pachytene → Diplotene
c) Leptotene → Zygotene → Pachytene → Diplotene → Diakinesis

Answer 1

Hint: Prophase1-It is the longest phase of meiosis1 that is also known as a reduction division. In prophase I, 3 important events take place that is- condensation of chromatin into the chromosome, next is the formation of synapsis, and finally crossing over. It is the longest phase and is divided into five sub-stages.

Complete answer:
Prophase 1 is the most complicated and longest phase of meiosis. It includes five sub-stages- Leptotene, zygotene, pachytene, diplotene, and diakinesis.
> Leptotene: In this phase chromatin network condenses. The long and thin thread-like chromosomes are formed. Each chromosome consists of two chromatids but appears as a single chromosome.

> Zygotene: In this phase, homologous chromosomes begin to pay-up, known as the pairing stage. These chromosomes are morphologically and genetically similar- one paternal and other maternal- present the diploid cell are called homologous chromosomes. This pairing is called synapsis. The pairs at this stage are called bivalents.

> Pachytene: During this phase condensation of chromosomes progresses. Chromosomes become short and thick. During this process crossing over, that is the exchange of genetic material between non-sister chromatids of homologous chromosomes takes place. This results in genetic recombination. The point where crossing over takes place is called chiasmata.

> Diplotene: In this stage, the homologous chromosomes repel each other and begin to separate. However, at the point of crossing over, they remain attached. The nuclear membrane starts disappearing.

> Diakinesis: In this phase, chromosomes start condensing and become short and separate. The separation of homologs proceeds and chiasmata gets shifted to the ends of chromatids. This is called terminalisation.

Hence, the correct answer is option (C).

Note: During this stage of prophase, chromatin condenses into chromosomes. The homologous chromosomes line up with each other and form pairs by a process called synapsis. Each pair of homologous chromosomes is called bivalent. Each bivalent has four chromatids, so it may also be called a tetrad. In homologous chromosomes, the two non-sister chromatids join each other at certain points along their length. These points of attachment are called chiasmata.