Gametogenesis
• Gametogenesis- is the formation of sex cells
(gametes) through the process of Meiosis.
– In males : Spermatogenesis (creation of sperm)
– In Females: Oogenesis (creation of ova [egg])
Spermatogenesis
• Occurs on the testes of a mature male.
• Begins as a diploid (2n) germ cell called a
spermatogonium.
• This cell enlarges and undergoes Meiosis 1 & 2
• Final product is 4 haploid (n) sperm cells.
– Each cell has equal amount of cytoplasm and the
same number of chromosomes.
• Sperm maturation occurs later to develop the
head and tail of the sperm.
Oogenesis
• Oogenesis occurs in ovaries of mature females
• Begins as diploid (2n) germ cell called a
oogonium.
• The oogonium enlarges and becomes the primary
oocyte. This cell enlarges and undergoes Meiosis
1 & 2, but the stages are not continuous.
• At the end of Meiosis 1 the cytoplasm is NOT
equally divided between the two cells.
– The cell that receives the most is the secondary
oocyte.
– The other cell is called a polar body and is not a viable
sex cell (usually dies)
• The secondary oocyte is then ovulated from
the ovary and undergoes Meiosis 2 only after
fertilization; again the cytoplasm again does
not divide equally.
– The cell with most of the cytoplasm becomes the
ovum (egg).
– The other becomes another polar body.
• Why the unequal distribution??
• To provide the ovum with sufficient nutrients
to support the developing zygote in the first
few days following fertilization.
• Meosis 1 and 2 are NOT continuous in humans
• Meiosis 1 begins in the ovarian tissues at birth
and does not continue beyond Prophase 1.
• The continuation of Meiosis 1 takes place after
the female reaches puberty. (one cell each
month)
• Meiosis 2 finishes AFTER fertilization of the
egg by the sperm.
• Know the table on Page 478.