Fertilization in Human

The fusion of the male gamete (sperm) and female gamete (ovum) to form a zygote is called fertilisation.

or

Formation of zygote by union of sperm and ovum is called as fertilization.

• Fertilisation in humans is the fusion of male and female gametes (sperm and ovum) and is an internal process occurring in the oviduct, leading to the formation of a diploid zygote.
• During copulation, millions of sperms are released into the vagina, but only one sperm reaches the ovum due to selection and protective barriers around the egg.
• Before fertilisation, sperm undergo capacitation and move towards the ovum; interaction between sperm and egg involves recognition molecules like fertilizin (ovum) and antifertilizin (sperm).
• The sperm’s acrosome releases enzymes that help digest the egg coverings (corona radiata and zona pellucida), allowing sperm entry through the membrane.
• After entry, the sperm nucleus and the ovum nucleus fuse (syngamy), forming a zygote (2n); this process restores the diploid chromosome number (46 in humans).
• Fertilisation triggers completion of meiosis II in the oocyte, formation of the second polar body, and formation of the female pronucleus and male pronucleus.
• In humans, sperm carry 22+X or 22+Y chromosomes, while ova carry 22+X only, determining the genetic sex of the offspring.