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

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

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

23 pairs of chromosomes Fig. 29-15

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 http://www.phschool.com/science/biology_place/labbench/lab3/homologs.html

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 2n 1 of the 2 copies of both chromosomes (1 maternal & 1 paternal) in each cell

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

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

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

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

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  4 (1n) cells with only 1 member of each pair of chromosomes

Interphase Prophase I Prophase II Metaphase I Metaphase II Anaphase I http://www.phschool.com/science/biology_place/labbench/lab3/homologs.html Interphase Meiosis I Meiosis II Prophase I Synapsis & crossing over occur Prophase II Tetrad Metaphase I Tetrads line up @ metaphase plate Metaphase II Chromosomes line up @ 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

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

Fig. 28-6 Crossover Some exchange of genetic material occurs at this stage of meiosis (synapsis) Increases genetic variation among offspring http://www.phschool.com/science/biology_place/labbench/lab3/homologs.html

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

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)

Mitosis vs. Meiosis Fig. 28-6

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.

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

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

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

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” http://www.astrographics.com Image copyright © Dennis Kunkel.

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. 28-15

Oogenesis: ovum production Fig. 28-15 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

Ovarian Cycle Follicle: ovarian structure, where oocyte grows & Meiosis I occurs Primary follicle: follicular cells grow/divide, several layers around primary oocyte Fig. 28-16

Ovarian Cycle Secondary follicle: (few of primaries further develop) inner and outer layers expand and separate generally only 1 @ day 8-10 of cycle Fig. 28-16

Ovarian Cycle Graffian (vesicular, tertiary) follicle: day 10-14 of cycle, creates a bulge in ovarian surface. Now formed, it will complete Meiosis I (had been suspended at Prophase I) Fig. 28-16

Ovarian Cycle Secondary oocyte + small polar body formed Secondary oocyte enters Meiosis II, stops at Metaphase II until fertilization Fig. 28-15

Ovarian Cycle Secondary oocyte & small polar body formed Secondary oocyte enters Meiosis II, stops at Metaphase II until fertilization Fig. 28-16

Ovarian Cycle Day 14-28: secondary oocyte releases from follicular wall through Ovulation: tertiary follicle releases secondary oocyte, into uterine tube Fig. 28-16

Ovarian Cycle Corpus luteum: endocrine structure created by follicle rupture of oocyte (lutea = yellow) Fig. 28-16

Reproductive Hormones: Males Fig. 28-12

Reproductive Hormones: Females Stimulates follicle devmt & oocyte maturation Stimulates ovulation Fig. 28-25

Reproductive Hormones: Summary