Question

Define fertilization and write the list of events occurring in human fertilization.

Answer 1

The evolution of fertilization is related to the origin of meiosis, as both are part of sexual reproduction, originated in eukaryotes. The gametes that participate in fertilization of plants are the pollen (male), and the egg (female) cell. The cycle of fertilization and the development of new individuals is called sexual reproduction.

Step by step answer: Fertilization is also known as insemination, pollination, syngamy, and impregnation is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Human fertilization is the union of a human egg and sperm, usually occurring in the ampulla of the fallopian tube. The result of this union is the production of a zygote cell, or fertilized egg, initiating prenatal development. The process of fertilization involves a sperm fusing with an ovum. The most common sequence begins with ejaculation during copulation, follows with ovulation, and finishes with fertilization.
After the sperm enters the cytoplasm of the oocyte, the tail and the outer coating of the sperm disintegrate and the cortical reaction takes place, preventing other sperm from fertilizing the same egg. The oocyte now undergoes its second meiotic division producing the haploid ovum and releasing a polar body. The sperm nucleus then fuses with the ovum, enabling the fusion of their genetic material.
When the sperm enters the ovum, receptors on the sperm head bind to the oocyte membrane. Once it’s bound, polyspermy then occurs. After approximately 40 minutes, the other receptors on the oocyte are lost from the membrane, causing it to no longer be fusogenic.
The oocyte completes its second meiotic division. This results in a mature ovum. The nucleus of the oocyte is called a pronucleus in this process, to distinguish it from the nuclei that are the result of fertilization. The sperm's tail and mitochondria degenerate with the formation of the male pronucleus.

Note: Upon gastrulation, which occurs around 16 days after fertilization, the implanted blastocyst develops three germ layers, the endoderm, the ectoderm, and the mesoderm, and the genetic code of the father becomes fully involved in the development of the embryo; later twinning is impossible.