Early in fetal development, 
primitivegerm cells in the 
ovaries differentiate into 
oogonia.In spermatogenesis, four functional sperm 
develop from each primary spermatocyte.The diploid(46 chromosomes) primary oocytes replicatetheir DNAand begin the first meiotic division, but 
the processstops in prophaseand the cells remain in this suspendedstate until puberty.Many of the primary 
oocytes degenerate before birth, but even with this decline, the two ovaries together contain approximately 
700,000 oocytes at birth.This is the lifetime supply, and no more will develop.If 
fertilizationoccurs, meiosis II continues,again this is an unequal division with all of the cytoplasm going to the 
ovum, which has 23 single-stranded chromosome.The large cellundergoes an unequal division so that nearly all the 
cytoplasm, organelles, and half the chromosomes go to one cell, which becomes a secondary oocyte.If fertilization 
does not occur, the second meiotic division is never completedand the secondary oocyte degenerates. These divide rapidly 
to form thousands of cells, still 
called oogonia,which have a 
full complementof 46 (23 
pairs) chromosomes.This is quite different than the 
male in which spermatogonia and primary spermatocytescontinue to be produced throughout the reproductive 
lifetime.