Name: The Cell Cycle and Its Regulation
Uploaded: 2019-07-19
Duration: 12 min 39 s
Description: Cyclins regulate the cell cycle only when they are tightly bound to Cyclin-dependent kinases (CDKs). Learn more about the cell cycle and its regulation in this video.

Question

Describe the prophase I of meiosis with suitable diagrams. What is the significance of this kind of division.

Accepted Answer

Meiosis is the complex type of cell division to form four daughter cells. It takes place in two stages: meiosis I and meiosis II. Prophase I is the longest phase of meiosis I that is divided into 5 substages: leptotene, zygotene, pachytene, diplotene and diakinesis.

Leptotene: The chromosomes start to appearing clearly as a result of condensation of chromatin fibres. In some cases, there is certain deeply stained area along the length of the chromosome and such regions are called chromomeres.

Zygotene: During this stage, two homologous chromosomes from male parent and female parent are attracted towards each other. The movement results from the attracting force that brings homologous chromosomes together. It is called chromosome pairing or synapsis. During synapsis, a special proteinaceous structure called the synaptonemal complex is formed. It is present in the space between two homologous chromosomes.

Pachytene: Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. It takes place during the pachytene stage of meiotic prophase I. Two non-sister chromatids undergo one or more transverse breaks at the same level. The break is followed by the interchange and fusion of broken ends between the two homologous chromosomes. This is called crossing over.

Diplotene: In this stage, the homologous chromosomes repel each other after recombination due to a decrease in the force of attraction between them. The separating chromosomes are held together at one or more points called chiasmata. It is the X-shaped structure formed between the non-sister chromatids as a result of crossing over and exchange of segments of DNA.

Diakinesis: It is the last substage of prophase I. When the paired homologous chromosomes begin to separate, the chiasmata are gradually pushed to the terminal end of the chromosome. This process is called terminalisation of chiasmata.

The main significance of meiosis are:

Meiosis maintains a definite and constant number of chromosomes in the cells of a particular species.

It leads to the formation of male and female gametes during sexual reproduction.

Through crossing over, meiosis provides an opportunity for the exchange of the genes and thus, causes genetic variation among the species that may play a significant role in evolution.

Describe the prophase I of meiosis with suitable diagrams. What is the significance of this kind of division.

Important Questions on Cell Division Cycle

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