-     also referred to as conception

Occurs when the ovum (or egg) from a female and a sperm from a male become combined.

Also occurs in plants, bacteria, and other organism in separate manners

When conception occurs than an embryo is formed

Depending on organism fertilization can be internal or external

Humans:

It is argued that once fertilisation occurs – then human life begins

A new organism is formed at this point

Where does it occur?

Fertilization can occur at any point from the ovaries to the vagina

It can also occur outside the reproductive tract such as the abdomen or other locations

The typical location is within the fallopian tube.

The Sperm

Movement of the sperm (swimming) occurs by a flagella or “a tail”

The sperm must find the egg to initiate fertilization

Once the sperm attaches to the egg it must pass through outer cell layers of the egg.

The sperm releases an enzyme that allows it to continue through the layers of cells

The Egg

Has several layers of cells

1.)   Corona radiata
2.)   Zona pellucida

Once sperm has entered through this layer a “cortical reaction” occurs

This reaction release enzymes from the egg that cause changes to occur through out the entire egg.

It no longer allows other sperm to pass through the cell layers

This allows or ensures that multiple sperm do not fertilize the same egg

Fertilization of the sperm and egg occur after the cortical reaction and the two gametes fuse together
and conception occurs.

Mitosis and Meiosis occur

Meiosis is essential for “sharing” or “transferring” of genetic material

Typically 1/2 of genetic genes come from sperm and 1/2 come from the egg

The egg is much larger than the sperm – due to the sperm only holds genetic material and the egg
provides nutrition and other necessary requirements of the embryo.

Therefore, due to the donation of chromosomes – each offspring will be genetically different from their parents but holding some similarities.