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:Human life begins when a sperm cell and an egg eel1 unite. The sperm
cell develops within the father， the egg cell within the mother. The
union ta~es place within the reproductive tract of the mother.after sex-
，uaFintereoursd: Ms in essence is the story of human reproduction.
Sex， always related to reproduction， also exists apart from it. The
meaning of sex ranges from the bodily differences between male and
~female to the complex drive responsible for life itself and for many of its
lJleasures and problems. We will begin our discussion of reproductiori and
sex with the bodily differences between male and female. Sex in this
sense is fixed at the instant the sperm and egg cells unite (conception).
BODILY DIFFERENCES BETWEEN
THE SEXES
In every sperm and egg cell there are t~~ microscopically
small bodies called chromosomqs~ which constitute the principal working
machinery of hered~f~， ~ng the determination of sex. All egg cells
have similar \"sex\" chromosomes (x). Half of the sperm cells have one
small \"sex\" chromosome (y) and the other half have an x similar to
that of the egg cell. If a ~ fferm cell with a y chromosome fertilizes an
egg cell， the individual is male (xy); otherwise it is female (xx). This
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