Question

Name the various stages of Prophase I of meiosis. During which phase does crossing

over occur? What is the significance of this process?​

Answer 1

Prophase-1 is the longest process it is divided into five stages namely

1) Laptotene

2) Zygotene

3) Pachytene

4) Dipolotene

5) Diakinesis

1) Laptotene: the chromosomes are thin and lightly visible

2) Zygotene: chromosome starts pairing between homologous chromosomes  form synaptomeal complex

3) Pachytene: bivalent clearly appears as tetrads

appearance of recombination nodules crossing over occurs

4) Dipolotene: dissolution of synaptomeal complex

tendency Recombinant homologous chromosomes of the bivalent separates from each other

5) Diakinesis: terminalization of chaismata

nucleus and nuclear membrane brake down

                  IMPORTANT POINTS

⭐It is the third stage of prophase I which occurs after zygotene.

⭐ Synapsed chromosome continue to become thick and short. The chromatids of homologous chromosomes appear as tetrad.

⭐ The most important step i.e., crossing over takes place where the exchange of genetic material between the non-sister chromatids of the homologous chromosomes occurs.

⭐ An enzyme-mediated process called recombination takes place. An enzyme recombinase is involved during this phase.

⭐ By the end of pachytene, the recombination between the homologous chromosome is complete and the two chromatids are linked at the site of crossing over.