Introduction

The human body, even with the many developments made in medicine, cannot be maintained forever. As a person ages the body suffers from a variety of degenerative changes and eventually it cannot function anymore. However, the genes of an individual can continue to live on, through sexual reproduction, in offspring. A combination of the genes from each of 2 parents is passed on and, thus, the offspring is not a clone/genetically identical to either of the parents or to each other.  This genetic diversity is critical to the survival and evolution of a species.

In order to reproduce sexually both parents must produce gametes (sex cells) that can meet and combine their genes into one structure.  

Fig. 1. Sperm penetration of the egg. Image courtesy Flickr under the creative commons license.

For reproduction to be successful the gametes must have 2 properties;

1. Motility so contact can be made: this role is fulfilled by the male gamete, the spermatozoon (sperm).

2. Nutrients for the developing embryo: a function of the female gamete, the oocyte (egg).

The process of egg and sperm union is termed fertilisation and constitutes the penetration of the egg by the sperm and the subsequent fusion of their genetic material; this event is the beginning of a miraculous process that gives rise to a whole new individual.

Banner image courtesy of Flickr under the creative commons license.