User:Clukatradford/sandbox

Life Cycle

Wild mice can survive to be up to four years of age though the prevalence of predators often shortens the average lifespan to within two years. Mice can begin breeding 50 days after birth, with females potentially having their first estrous cycle from twenty-five to forty days from birth. Mating occurs at night and initiates ovulation in the female. Early development follows fertilization with: cleavage, gastrulation, neurulation, and axis formation. Litter sizes range from about ten to twelve pups with each pup born nude, blind, and earless about twenty days after fertilization.

Fertilization

Haploid gametes develop from meiosis of germ cells starting in embryogenesis. Post-meiosis, sperm cells have condensed their DNA and modified their organelles for fertilization. The nucleus is headed by an acrosome and tailed by centrioles, mitochondria. The overall shape of the cell is elongated; most of the cytoplasm is extended into the flagellum (source?). Egg, or oocyte, cells are arrested in metaphase II of meiosis; completion of meiosis does not occur until after fertilization. Egg cells are secreted into the oviduct following mating as cumulus cells, oocytes enveloped in a zona pellucida and surrounded by follicle cells.

Following mating, sperm cells navigate to the oviduct, completing capacitation during this time. Fertilization of the oocyte occurs within the oviduct. Sperm cells bind to the zona pellucida by interacting with ZP3 and ZP2. The initial interaction between the sperm cell and ZP3 activates the acrosomal reaction: the contents of the acrosome are released to digest the zona pellucida. Sperm-egg recognition is carried out at the egg surface with ADAM and integrin bindings. There is a preference for binding at the equatorial region, ninety degrees from the location of the first polar body; sperm binding influences cleavages at later development stages and unfavorable binding points reduces the ability to properly distribute transcription factors. Once bound, plasma membranes of both gametes fuse and the remaining contents of the sperm are integrated into the egg.

Following fusion, intracellular calcium levels begin to oscillate and meiosis is resumed. Cortical granules are released and migrate to the plasma membrane and modifying receptors to block fusion by more sperm. A second polar body is expelled with the completion of the final meiotic division. DNA replication occurs within the paternal and maternal nucleus. The finished chromosomes align with the maternal spindle fibers prior to cleavage. Clukatradford (talk) 12:48, 21 March 2018 (UTC)