Prophase I vs Prophase II
Cell division is an important process for all living organisms. Sexual reproduction is mainly found in eukaryotes. The formation of gamete is vital for sexual reproduction. All eukaryotes have a unique chromosome number for each species. To maintain the chromosome number in a constant value from one generation to another, it is essential to reduce the chromosome number by half in gametes and return to the full amount after fertilization. To carry out this process, a special type of nuclear division called “Meiosis” occurs in cells. In Meiosis, two subsequent nuclear divisions occur. They are known as Meiosis I and Meiosis II. Four haploid cells are resulted at the end of the Meiosis. Meiosis I reduces the ploidy level whereas Meiosis II divides resulting daughter cells in a mitosis-like process. Meiosis I is subdivided into four phases called Prophase I, Metaphase I, Anaphase I, and Telophase I, and Meiosis II is sub divided as Prophase II, Metaphase II, Anaphase II, and Telophase II.
Prophase I is found in Meiosis I. The chromosomes become visible in Prophase I and synapse to form tetrads. Resulting tetrads contain two pairs of chromosomes; therefore, known as “bivalents”. Crossing over is an important process happens in Prophase I which allows the chromosomes to exchange genetic materials and to produce more different recombinants. The crossing over points in chromosomes are called “Chiasmata”. Disappearing of nuclear envelope, moving the spindle into the center, and connecting the tetrads to the spindle fibers by Kinetochores are the other processes that occur in Prophase I.
Prophase II can be found in Meiosis II. It is the beginning of another subsequent cell division after Meiosis I without an Interphase. This process is identical to the Prophase found in Mitosis, in many aspects. Only difference is the half amount of chromosomes in Prophase II. Also, the process of pairing chromosomes cannot be seen here. The breakdown of nuclear envelops, which formed in Telophase I also occur in this phase. No crossing over occurs here like in Prophase I.
What is the difference between Prophase I and Prophase II?
• Prophase I is the beginning phase of Meiosis I while Prophase II is the beginning phase of Meiosis II.
• There is a long interphase before Prophase I, whereas Prophase II occurs without an interphase. It directly goes from Telophase I to prophase II.
• The pairing of homologous chromosomes occurs in Prophase I, whereas such process cannot be seen in Prophase II.
• The process of crossing over and formation of “Chiasmata” is unique to Prophase I while it is not found in Prophase II.
• The exchange of genetic materials to produce different recombinants is also occurs in Prophase I, but it is not possible in Prophase II.