1. GAMETE FORMATION
(Homo sapiens)

2. SPERMATOGENESIS Growth and maturation Anaphase I Human 65 days
Spermatogonium
(stem cell)
Growth and
maturation
Primary Spermatocyte
Prophase I
Metaphase I
2N = 4 (humans 2N = 46)
Anaphase I

3. Anaphase II Spermiogenesis Secondary Spermatocytes Spermatids Sperm
Prophase II
Metaphase II
N = 2 (humans N = 23)
Anaphase II
Spermatids
N = 2 (humans N = 23)
Spermiogenesis
Sperm
Four functional cells
N = 2
(humans N = 23)

4. OOGENESIS Growth and maturation Anaphase I Oogonium (stem cell)
Divide mitotically beginning at 2 months gestation until about 7 million cells (6-7 months gestation)
All but 1-2 million die
Growth and maturation
Primary Oocyte
Remains in a modified Diplotene stage
2N = 4 (humans 2N = 46)
Resume meiosis at about 12 years of age & continue until about 45 years (mature eggs may be 12 to 45 years of age)
Anaphase I

5. Anaphase II Secondary Oocyte & 1st Polar Body
About 400, one day longevity
Cytoplasm conserved for ovum
N = 2 (humans N=23)
Secondary oocyte dies at metaphase II if no sperm penetration
Oocyte
1st
Polar
body
Anaphase II
Ovum & 2nd Polar Body
One functional cell
N = 2 (humans N=23)
Male & female pronuclei fuse to form zygote
Polar bodies degenerate
Ovum
2nd Polar bodies
Male pronucleus