NEET BIOLOGY

Detailed explanation-1: -Fertilization. Meiosis-II is completed on fertilization. This gives off a third polar body. If the fertilization does not occur, the oocyte degenerates 24 hours after ovulation while remaining arrested in meiosis-II cell division.

Detailed explanation-2: -Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II. However, this process is also halted at the metaphase II stage until fertilization, if such should ever occur.

Detailed explanation-3: -Following fertilization, the egg exits from meiosis and assembles a haploid pronucleus. At the same time the sperm genome, which enters the egg in a highly compact state, undergoes decompaction. Sperm protamines are replaced by histones and the male haploid pronucleus is formed.

Detailed explanation-4: -First meiotic division starts before delivery of the female foetus and is completed within tertiary follicle of ovary. Meiotic division of the secondary oocyte is completed at the time of fusion of a sperm with an ovum.

Detailed explanation-5: -After ovulation the oocyte is arrested in metaphase of meiosis II until fertilization. At fertilization, the secondary oocyte completes meiosis II to form a mature oocyte (23, 1N) and a second polar body.