Kallie
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- Meiosis
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Meiosis 1 (reductional division)
Prophase1, Metaphase1, Anaphase 1, Telophase 1
Meisosis 2 (equatorial division)
Prophase 2, metaphase 2, anaphase 2, telophase 2 (like mitosis) - Prophase 1
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Tetrads form
chromatin condenses into visible chromosomes - Tetrad
- Homologus Paternal and maternal chromosomes pair via synaptonemal complex
- Letptotene
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Chromosomes condense
Pairing of homologus dyads (prs of sister chromatids) - Zygotene
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Synaptonemal complex forms
DNA strands of nonsister chromatids start recombination - Pachytene
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Synapsis complete
Recombination nodules appear (at least one for each pair)
Enzymes for DNA combination and repair - Diplotene
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Recombination complete
Synaptonemal complex begins to breakdown
Chiasmata appear at recombination nodes, migrate towards end of chromatids - Diakinesis
- Chromosomes condense further
- Metaphase I
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Homologous prs of chromosomes align on equatorial plate of spindle
Spindle fibers from either pole attach to kinetochore - Anaphase I
- Pair of chromatids separate at centromere
- Telophase I
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Like mitotic telophase
Each daughter has 23 chromosomes
2 non identical sister chromatids
diploid DNA - Meiosis II
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Interphase with no DNA replication
Other steps like mitosis
Daughter cells have 23 chromosomes but a haploid DNA - Nondisjunction
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the failure of chromosomes to correctly separate:
homologues during meiosis I or
sister chromatids during meiosis II - Monosomy
- Missing one chromosome
- Trisomy
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Three of the same chromosome
Lethal, except for 13. 18, and 21 and X - Spermatogenesis
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Primordial germ cells (46,2n) testes week 4 of emryogenesis
Type A Spermatogonia – mitosis to produce stem cells
Type B Spermatogonia (46, 2n) ïƒ primary spermatocytes (46,4n) --> 2 secondary spermatocytes (23,2n) -->meiosis II ïƒ 4 spermatids (23, 1n) ïƒ sperm (23,1n) - Capacitation
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Occurs in female reproductive tract
Unmasking of sperm glycosyltransferases
Removal of surface coat of sperm - Oogenesis
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Primordial germs cells (46,2n) in ovary week 4 of embryogenesis oogonia (46,2n)meiosis I primary oocytes (46,4n) all formed by 5th month of fetal life, remain in diplotene of prophase until puberty
Secondary oocyte (23, 2n) and 1st polar body formed during ovarian cycle
Enters meiosis II and ovulation occurs at metaphase, remain there until fertilization mature oocyte (23,1n) and 2nd polar body formed after fertilization - Ovarian Cycle
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Hypothalamus GNRH adenohypophysis FSH & LH
FSH2° follicle graafian follicle within the ovary
Granulosa cells of 2° and graafian follicle estrogen
Estrogen endometrium enters proliferative phase
LHovulation
Granulose lutein cells of corpus luteum progesterone endometrium into secretory phase - Menstrual Cycle
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1) 1-4ïƒ menstruation ïƒ necrosis and shedding of endometrium
2) 4-15 ïƒ proliferative phase ïƒ regeneration of functional layer of endometrium, low basal body temperature (97.5°F)
3)14-16ïƒ ovulatory phase ïƒ ovulation of 2° oocyte and ↑ LH
4) 15-25 ïƒ secretory phase ïƒ endometrial gland secretion, body temp ↑98° implantation occurs
5) 25-28 ïƒ premenstrual phase ïƒ ischemia due to reduced blood flow to endometrium - Acrosomal Reaction
- Sperm binds to zona pellucida of 2° oocyte releasing acrosomal enzymes penetration of ZP cortical reaction 2° oocyte impermeable to other sperm
- Male Pronucleus
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Nucleus of the sperm
No tail or mitochondria from sperm - Female Pronucleus
- Nucleus of the ovum
- Zygote
- Male and female pronucleus fuse to form zygote
- Cleavage
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Series of mitotic divisions of zygote
Zygote blastula morula (32 cell stage) - Morula
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32 cell stage
Inner cell mass
Outer cell mass - Blastomere
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Mitotically dividing zygote cells,
Totipotent til 8 cell stage (can form whole new embryo) - Blastocyst Formation
- Morula secretes blastocyst cavity
- Embryoblast
- Inner cell mass that becomes the embryo
- Trophoblast
- Outer cell mass becomes part of the placenta
- embryoblast gives rise to bilaminar embryonic disk
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epiblast --> amniotic cavity
hypoblast --> yolk sac - prochordal plate
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fusion of epiblast and hypoblast cells
marks future site of mouth - syncytiotrophoblast
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grows into endometrium to contact blood vessels and glands
not divide mitotically
produces HCG (human chorionic gonadotropin) - cytotrohoblast
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divides mitotically
primary chorionic villi protrude into the syncytiotrophoblast - extraembryonic mesoderm
- derived from epiblast
- extraembryonic somatic mesoderm
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lines cytotrophoblast
aka somatopleuric mesoderm
forms connecting stalk (suspends within chorionic cavity)
covers amnion - chorion
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Wall of the chorionic cavity
1. extraembryonic somatic mesoderm
2. cytotrophoblast
3. syncytiotrophoblast - extraembryonic visceral mesoderm
- splanchnopleuric mesoderm
- Human Chorionic Gonadotropin (HCG)
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syncytiotrophoblast produces HCG
stimulates progesterone by corupus luteum (maintains function)
luteal progesterone needed for maintenence of pregnancy til week 8 when placenta takes over
-Day 8 in maternal blood, day 10 in urine (pregnancy testing)
low HCG --> miscarriage or ectopic
high HCG --> multiple pregnancy or other problems - week 3
- epiblast
- Germ layers
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ectoderm --> epidermis, nervous system
endoderm --> GI tract and organs, respiratory passages and organs
mesoderm--> muscles, connective tissue - gastrulation
- formation of primitive streak, notochord, germ layers
- primitive streak
- thickened band of epiblast cells, appears caudally in the midline of embryonic disk
- primitive knot (Hansen's Node)
- cranial end of embryonic disk
- Mesoderm
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epiblast cells multiply and migrate towards the primitive streak then through its groove
spread laterally and cranially to form intraembryonic mesoderm between epiblast and hypoblast