Final answer:
Meiotic arrest in mammals and amphibians is a regulated process where meiosis is paused at specific stages in oocyte development until the appropriate time, such as puberty or ovulation, to ensure readiness for fertilization.
Step-by-step explanation:
The process of meiotic arrest refers to the halting or pausing of meiosis at specific stages. In female mammals and amphibians, the primary oocytes begin meiosis before birth but are arrested in the first prophase stage. When a female reaches adolescence, hormones stimulate the resumption of meiosis, resulting in the division of a primary oocyte into a secondary oocyte and a small polar body that typically degenerates. At this point, a secondary meiotic arrest occurs at the metaphase II stage.
At ovulation, the secondary oocyte is released and can be fertilized. If fertilization takes place, the secondary oocyte completes meiosis II, creating another polar body and an ovum, which then combines with a sperm cell to form a diploid zygote.
Meiotic arrest is a critical factor in the production and development of oocytes, ensuring that the egg cell is ready for fertilization at the optimal time. The regulation of this arrest and the eventual resumption of meiosis are crucial for successful sexual reproduction. This process, along with X inactivation, contributes to the genetic regulation and diversity in mammals.