Fertilization - Genes - the units of inheritance (2/10)

Uploaded by OUlearn on 25.07.2008

The egg, surrounded by a jelly-like coat,
is only about a tenth of a millimetre in size,
no larger than the tip of a pin.
To stand any chance of being fertilised,
the egg must travel down the Fallopian tube,
which links the ovaries to the womb.
Travelling in the opposite direction are the sperm,
which have been released into the woman's vagina.
Of the 400 million or so ejaculated into the vagina,
only 100 will make it to the vicinity of the egg.
Within the head of all sperm are special enzymes.
When contact is made, a chemical reaction
makes the membrane at the head of the sperm rupture.
Powerful enzymes are released
which break down the egg's jelly-like coat
and allow the chromosomes of the sperm to enter.
After fertilisation, other sperm are prevented from entering
by changes in the egg cell membrane and its outer coat.