Spermatogenesis & Oogenesis

1. Spermatogenesis & Oogenesis • Pg. 103-104

2. Spermatogenesis • Occurs in the seminiferous tubules of the testes • the formation of sperm • Takes 65 to 70 days

3. Spermatogenesis Overview • Begins with one cell • Which becomes two • Finally four

4. Primary Spermatocytes • These are the basic cells, where process begins • Diploid • Produced continuously by mitosis

5. Sperm cells • Also haploid, are produced when secondary spermatocytes divide

7. Question: • T/F: A woman is born with all the eggs she will ever have

8. Answer: • Technically not true! • A woman is born with all the primary oocytes she will ever have • They will become eggs later • This probably is the reason why chances of Down’s syndrome increase with mother’s age

9. 7th Inning Stretch • Launch

10. Oogenesis • Occurs in the ovaries • Formation of oocytes, eggs • Begins prior to birth! • Spans all of pre-reproductive & reproductive life

11. Oogenesis Overview • Begins with one cell • Which becomes two • Then finally, four

12. Primary Oocyte • These are present at birth • Stay dormant until sometime after puberty..things get kinky • Diploid (2n) • 46 chromosomes

13. First Polar Body • Results from meiosis I • Smaller (has less cytoplasm)

14. Secondary Oocyte • Released by ovulation • Happens roughly every 28 days

15. Fertilization • Sperm penetrates secondary oocyte • Triggers meiosis II • Oocyte’s nucleus divides • One nucleus stays, combines with sperm’s nucleus • Other nucleus leaves

16. Down’s Syndrome • Much more likely with older moms • 3 copies of chromosome 21 • Caused by non-disjunction of chromosomes • Could this occur in meiosis II? • Why are mistakes more likely with older oocytes?

17. Question • What cell division process is used in spermatogenesis? • In oogenesis? • How do they differ?

18. Answer • Both spermatogenesis and oogenesis use meiosis • Spermatogenesis needs many, many parent cells—provided by mitosis