Why is a second polar body expelled after fertilisation?

The second polar body is expelled after fertilization as a result of the completion of meiOSis in the oocyte. When a sperm fertilizes the egg, it triggers the final stages of meiOSis, leading to the division of the oocyte into a mature ovum and the second polar body. This process ensures that the egg retains the correct haploid number of chromosomes while discarding the excess genetic material. The expulsion of the polar body is crucial for maintaining genetic balance in the resulting zygote.