This Short Essay provides information about the process of Fertilization in an Organism!
Fertilization is a complex process which involves the fusion of male and female gametes followed by the fusion of their cytoplasm.
Fertilization begins with the sperm’s approach to the egg and ends with the fusion of egg and sperm pronuclei. It involves a series of events.
The process of fertilization has dual independent functions:
(i) to cause the egg to start developing i.e. Activation, and (ii) to inject a male haploid nucleus into the egg cytoplasm, i.e. Amphimixis.
Activation involves (i) the completion of second maturation division, if not occurred earlier; (ii) the egg cortex to form fertilization membrane outside the plasma membrane; (iii) the egg cytoplasm to start various metabolic reactions; and (iv) stimulation of mitosis for cleavage by contribution of sperm’s Centriole to the egg. Amphimixis is the most important event occurring in the life of all animals and plants and involves (i) the intermingling of paternal and maternal hereditary characters in the offspring; (ii) restores the diploid state of animal cell; and (iii) includes genetic variations in the species. The genetic variations provide the raw materials to the natural selection for speciation (species formation).
The process of fertilization has been studied mostly in marine invertebrates, such as, sea urchins, polychaetes, echinroids etc. whose eggs are typically translucent and without much yolk. Among vertebrates most fertilization studies have been done in amphibians and mammals.
Attention has been focussed on amphibians because they are available and suitable for analytical and experimental procedures, and on mammals because man himself is a mammal and the need to know what happens is great.