1. Physiology of Reproduction: Gametogenesis and the Female Cycle
Exercise 43
Physiology of Reproduction: Gametogenesis and the Female Cycle

2. Objectives:
Haploid, diploid, homologous chromosomes, sister chromatids, synapsis, crossover
Events & endproducts of Meiosis I and Meiosis II
Spermatozoa and ovarian structures
Reproductive hormones & functions

3. CHROMOSOMES Chapter 3 Cell Division
Mitosis, Meiosis
DNA coils and coils during cell division to form chromosomes
Fig. 3-14

4. 23 pairs of chromosomes
Fig

5. CHROMOSOMES Homologous chromosomes: members of a chromosomal PAIR
1 comes from mom, 1 comes from dad
Sister chromatids: each “half” of the same chromosomal pair
Each chromosome consists of 2 duplicate chromatids
Darker color
Lighter color
Mitosis or
Meiosis I

6. Fig. 28-7
PLOIDY
Diploid cells (2n) contain TWO (both) members of each pair of chromosomes
Majority of your cells (somatic cells)
23 pairs of chromosomes
Endproduct of MITOSIS
2n n
1 of the 2 copies of both chromosomes (1 maternal & 1 paternal) in each cell

7. MITOSIS: somatic cells
Interphase
Prophase
Metaphase
Anaphase
Telophase
2 (2n) daughter cells with 23 pairs of chromosomes  46 chromosomes, maternal & paternal copies
Fig. 28-6

8. MITOSIS: somatic cells
INTERPHASE
PROPHASE
METAPHASE
Fig. 3-29

9. MITOSIS: somatic cells
2 (2n) daughter cells with 23 pairs of chromosomes
46 chromosomes, maternal & paternal copies
Fig. 3-29
ANAPHASE
TELOPHASE
CYTOKINESIS

10. 1 copy of either maternal or paternal chromosome in each cell
Fig. 28-6
PLOIDY
Haploid cells (1n) contain only ONE member of each pair of chromosomes
23 “chromosome halves”
Endproduct of MEIOSIS
Sex cells/Gametes: sperm cells, egg cells
1n 1n 1n 1n
1 copy of either maternal or paternal chromosome in each cell

11. MEIOSIS: sex cells ONLY
Interphase I  Meiosis I:
Prophase I, Metaphase I, Anaphase I, Telophase I (cytokinesis I)
Interphase II  Meiosis II:
Prophase II, Metaphase II, Anaphase II, Telophase II (cytokinesis II)
Two cycles of cell division  (1n) cells with only 1 member of each pair of chromosomes

12. Interphase Prophase I Prophase II Metaphase I Metaphase II Anaphase I
Interphase
Meiosis I
Meiosis II
Prophase I
Synapsis & crossing over occur
Prophase II
Tetrad
Metaphase I
Tetrads line metaphase plate
Metaphase II
Chromosomes line metaphase plate
Anaphase I
Homologous pairs separate
Anaphase II
Sister chromatids separate
Telophase I
Telophase II
Cytokinesis I
Cytokinesis II
4 (1n) cells formed, each w/only 1 chromosome of each homologous pair

13. SYNAPSIS
In meiosis, maternal & paternal chromosomes (homologous chromosomes) come together & pair up
(matched set of 4 chromatids = tetrad)
Fig. 28-6

14. Fig. 28-6
Crossover
Some exchange of genetic material occurs at this stage of meiosis (synapsis)
Increases genetic variation among offspring

15. End Meiosis II: the sister chromatids separate
Fig. 28-6
End Meiosis I: Both copies (sister chromatids) of either the maternal chromosome or the paternal chromosome in each cell
End Meiosis II: the sister chromatids separate
1n 1n 1n 1n

16. MEIOSIS—different from Mitosis
Anaphase I—tetrads break up—maternal & paternal (homologous) chromosomes separate
After meiosis I, have both copies of either maternal OR paternal chromosomes from each tetrad
Then maternal/paternal chromosomes are randomly distributed into two daughter cells at end of meiosis I
Anaphase II: Sister chromatids separate
Telophase II: 4 (1n) cells with only 1 member of each pair of chromosomes (23)

17. Mitosis vs. Meiosis
Fig. 28-6

18. MEIOSIS
MITOSIS
Interphase
Begins with a diploid cell
4 chromosomes combine to form 2 tetrads
Prophase
The chromosomes in the tetrad cross over each other, allowing them to exchange genetic material
4 chromatids combine to form two chromosomes linked by a centromere
Metaphase
The two tetrads line up in the center
The two chromosomes line up in the center
Anaphase
The two tetrads split up into four chromosomes which go to both poles
The two chromosomes split up into four chromatids which move to both of the poles (2 each)
Telophase
The two sets of chromosomes are enclosed by the nuclear envelope
The two sets of chromatids are enclosed by the nuclear envelope
Cytokinesis
Two cells are formed with two sets of chromosomes in each one
Two cells are formed with two chromatids in each one Mitosis is now complete.

19. MEIOSIS
MITOSIS
Prophase II
DNA replication is skipped and the two cells’ nuclear envelopes are dissolved and the spindle reformed The four chromatids in each cell are connected together to form two chromosomes
Metaphase II
The two chromosomes line up in the center
Anaphase II
The two chromosomes are split up into their daughter chromatids and move towards opposites poles
Telophase II
The nuclear envelope is reformed around the two poles on each cell.
Cytokinesis
The cells are split up again and four haploid cells result Meiosis is now complete

20. Spermatogenesis: sperm production
Fig. 28-7
Spermatogonia undergo mitotic divisions throughout normal adult life
Daughter cells move to the lumen of seminiferous tubule and differentiate into primary spermatocytes
Meiosis produces gametes (spermatids)
Spermiogenesis: spermatids develop into haploid spermatozoa

21. Spermatozoa Anatomy Head: flattened ellipse, contains DNA
Acrosome: tip of head, membrane “cap”—has enzymes to aid fertilization
Nucleus: in head, contains DNA
Midpiece: mitochondria arranged in a spiral, provide ATP for tail movement
Tail: flagellum—corkscrew movement
Fig. 28-8

22. Mature spermatozoon No ER No golgi apparatus No lysosomes
No peroxisomes or many other parts
Reduces cell’s mass and size
“Carrier for the chromosomes”
Image copyright © Dennis Kunkel.

23. Oogenesis: ovum production
Begins before birth, peaks at puberty, ends at menopause
Ovarian cycle—monthly (pubertymenopause)
Oogonia complete mitosis before birth, then primary oocytes go through Prophase I and stop until puberty
Fig

24. Oogenesis: ovum production
Fig
Monthly after puberty, some primary oocytes continue development
Polar bodies: nonfunctional cells, later disintegrate; result of meiotic division
Primary Secondary oocyte halts at Metaphase II until fertilization

25. Ovarian Cycle
Follicle: ovarian structure, where oocyte grows & Meiosis I occurs
Primary follicle: follicular cells grow/divide, several layers around primary oocyte
Fig

26. Ovarian Cycle Secondary follicle:
(few of primaries further develop) inner and outer layers expand and separate
generally only day 8-10 of cycle
Fig

27. Ovarian Cycle
Graffian (vesicular, tertiary) follicle: day of cycle, creates a bulge in ovarian surface.
Now formed, it will complete Meiosis I (had been suspended at Prophase I)
Fig

28. Ovarian Cycle Secondary oocyte + small polar body formed
Secondary oocyte enters Meiosis II, stops at Metaphase II until fertilization
Fig

29. Ovarian Cycle Secondary oocyte & small polar body formed
Secondary oocyte enters Meiosis II, stops at Metaphase II until fertilization
Fig

30. Ovarian Cycle
Day 14-28: secondary oocyte releases from follicular wall through
Ovulation: tertiary follicle releases secondary oocyte, into uterine tube
Fig

31. Ovarian Cycle
Corpus luteum: endocrine structure created by follicle rupture of oocyte (lutea = yellow)
Fig

32. Reproductive Hormones: Males
Fig

33. Reproductive Hormones: Females
Stimulates follicle devmt & oocyte maturation
Stimulates ovulation
Fig

34. Reproductive Hormones: Summary