Reproductive life cycle in
animals
Dioecious organisms occur as
two separate sexes, male
and female. They
are formed by the union of two haploid (n)
gametes (each with
one set of chromosomes), an egg from the female and a sperm from the male, to
form a diploid (2n) zygote. Cells in the
zygote undergoes a series of duplication divisions (mitosis)
to form the adult. In the germline
of the adults, diploid meiocytes undergo a series of equational & reduction
divisions (meiosis)
that produce four haploid gametes. In humans, as in most mammal
species, all four male gametes
survive, whereas typically only a single female egg grows to maturity.
Figure ©2002 by Griffiths et al.; all text material ©2014 by
Steven M. Carr