Spermatogenesis and Oogenesis
Meiosis, the process by which gametes are formed, can
also be called gametogenesis, literally “creation of
gametes.” The specific type of meiosis that forms sperm is called
spermatogenesis, while the formation of egg cells, or ova, is called
oogenesis. The most important thing you need to remember about both
processes is that they occur through meiosis, but there are a few
specific distinctions between them.
Spermatogenesis
The male testes have tiny tubules containing diploid cells
called spermatogonium that mature to become sperm. The basic function
of spermatogenesis is to turn each one of the diploid spermatogonium
into four haploid sperm cells. This quadrupling is accomplished through
the meiotic cell division detailed in the last section. During interphase
before meiosis I, the spermatogonium’s 46 single chromosomes are
replicated to form 46 pairs of sister chromatids, which then exchange
genetic material through synapsis before the first meiotic division.
In meiosis II, the two daughter cells go through a second division
to yield four cells containing a unique set of 23 single chromosomes
that ultimately mature into four sperm cells. Starting at puberty,
a male will produce literally millions of sperm every single day
for the rest of his life.
Oogenesis
Just like spermatogenesis, oogenesis involves the formation
of haploid cells from an original diploid cell, called a primary
oocyte, through meiosis. The female ovaries contain the primary
oocytes. There are two major differences between the male and female
production of gametes. First of all, oogenesis only leads to the
production of one final ovum, or egg cell, from each primary oocyte
(in contrast to the four sperm that are generated from every spermatogonium).
Of the four daughter cells that are produced when the primary oocyte divides
meiotically, three come out much smaller than the fourth. These
smaller cells, called polar bodies, eventually disintegrate, leaving
only the larger ovum as the final product of oogenesis. The production
of one egg cell via oogenesis normally occurs only once a month,
from puberty to menopause.
