Name: Cell Cycle: The M Phase
Uploaded: 2019-07-19
Duration: 9 min 36 s
Description: After the Interphase, the cell is ready to divide! Let's check out this quick video lesson to learn the different processes that take place in the M Phase.

Question

With help of illustration, explain the various stages of meiosis I. What is the biological significance of first meiotic division?

Accepted Answer

Meiosis I is the first stage of reduction division and it includes karyokinesis and cytokinesis. Karyokinesis is divided into four stages: prophase I, metaphase I, anaphase I and telophase I. Prophase that is divided into five stages: leptotene, zygotene, pachytene, diplotene, and diakinesis.

Leptotene: The chromosomes start to appearing clearly as a result of condensation of chromatin fibres.

Zygotene: During this stage, two homologous chromosomes are attracted towards each other. It is called chromosome pairing or synapsis.

Pachytene: Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes. It takes place during the pachytene stage.

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.

Diakinesis: This is when the homologous chromosomes continue to separate as the chiasmata move to the opposite ends of the chromosomes.

Metaphase I:
Homologous chromosomes remain joined and are arranged in the metaphase plate. Spindle fibres are attached on the centromeres via kinetochore of the chromosomes.

Anaphase I:

Homologous chromosomes are detached from each other and each is lying at opposite poles with their two chromatids.

Telophase I:
The chromosomes return to their uncondensed forms. Nuclear membrane and nucleolus are reappeared.

The division of the cytoplasm is called cytokinesis that occurs simultaneously with telophase I, resulting to two haploid daughter cells.

Significance of Meiosis-I:
• Meiosis separates the homologous chromosomes and reduces the chromosome number to one half. This is essential for sexual reproduction for the production of gametes.
• Crossing over occurs during this division. It introduces new combinations of genes or recombinations. Recombinations result in variations.

With help of illustration, explain the various stages of meiosis I. What is the biological significance of first meiotic division?

Important Questions on Cell Cycle and Cell Division

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