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Historic drawing of human oocyte andspermatozoa

Lecture - FertilizationIntroduction

This lecture will cover male andfemale gametogenesis andfertilisation.

IN development 1 embryonic cell(zygote) will produce about 1013

(100,000,000,000,000) cells in theadult at any one time (over timewith cell death and ongoingreplacement this is substantiallymore).

This is where the first embryonic cell begins! Fertilization is the fusion ofhaploid gametes, egg (oocyte) and sperm (spermatozoa), to form thediploid zygote. Note though there can be subtle differences in thefertilization process which occurs naturally within the body or throughreproductive technologies outside the body, the overall product in bothcases is a diplod zygote.

Lecture - Print PDF

Also use the previous lecture recording (below) to help understand thisonline content.

2016 Lecture Video Recording

Some Recent Research

Lecture Archive: 2016 Video | 2016 PDF | 2015 | 2015 PDF | 2014 PDF |2013 | 2012 | 2011 | 2010 | 2009

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Lecture Objectives

1. Broad understanding of reproductive cycles.2. Understand the key features of gametogenesis.3. Understand the differences in male and female gametogenesis.4. Brief understanding of the differences between mitosis and meiosis.5. Understanding of the events in fertilization.

Male - spermatogenesis

Lecture Resources

Movies

References

Human Reproductive Cycle

Sexual reproduction in most species is regulated by regular endocrinechanges, or cycles, in the female. These cycles begin postnatally, functionfor variable times and can then decrease or cease entirely.

Human reproduction is regulated in females by the menstrualcycle, a regular cyclic hormonal change which coordinate changes inthe ovary and internal reproductive tract. This cycle commences atpuberty and ends at menopause.Non-primates (rats, mice, horses, pig) reproduction is regulated infemales by the estrous cycle (British spelling, oestrous).

Female MaleMenstrual Cycle a regular cycle ofreproduction (28 days)begins at puberty, release of 1 egg(oocyte) every cycle

continuous production of sperm(spermatozoa)begins at puberty, release millionsof spermatozoa

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Endocrine controlled (HPG axis)Hypothalamus - Pituitary -Gonad

Endocrine controlled (HPG axis)Hypothalamus - Pituitary -Gonad

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Gametogenesis

Meiosis in the gonad (ovary or testis) produces the haploid gametes, oocyteand spermatozoa (egg and sperm). Meiosis time course and final gametenumber differs between female and male.

Male - Spermatogenesis

Human spermatozoa (electron microscope)

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Mouse spermatozoa (electron microscope)

The testes have two functions.

1. produce the male gametes or spermatozoa2. produce male sexual hormone, testosterone (internal and external

genitalia, sex characteristics)

Historic testis drawing

Child Seminiferous tubule

Adult Seminiferous tubule

Seminiferous tubule cross-section and supporting cells

Human spermatozoa take about 48 days from entering meiosis untilmorphologically mature spermatozoa.

Spermatogonia - are the diploid first cells of

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spermatogenesisPrimary spermatocytes - large, enter theprophase of the first meiotic divisionSecondary spermatocytes - small, completethe second meiotic divisionSpermatid - immature spermatozoaSpermatozoa - differentiated gamete

Spermatozoa development:primordial germ cell - spermatogonia -primary spermatocyte - secondaryspermatocytes - spermatid - spermatozoa

Sertoli cells (support cells)

Interstitial cells or Leydig cells (producehormone)

Female - Oogenesis

The ovaries have two functions.

1. produce the female gametes or oocytes2. produce female hormones, estrogen and progesterone (secondary sex

characteristics, menstrual cycle)

three stages of follicle development

In an adult human female the development of a primordial folliclecontaining an oocyte to a preovulatory follicle takes in excess of 120 days.

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Human Follicle Development

Human Ovulation

Human ovary follicle development

Ovarian Follicle Stages: primordial follicle - primary follicle -secondary follicle - tertiary follicle - preovulatory follicle

Follicle cells (support cells) Theca cells (produce hormone)

Ovulation Movie

Meiosis Differences

Types of Cell Division

Male Meiosis

Meiosis initiated continuously in a mitoticallydividing stem cell population4 gametes produced / meiosisMeiosis completed in days or weeksMeiosis and differentiation proceed continuouslywithout cell cycle arrestDifferentiation of gamete occurs while haploid aftermeiosis endsSex chromosomes excluded from recombinationand transcription during first meiotic prophase Male gametogenesis

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MBoC - Figure 20-27. The stages of spermatogenesis

Female Meiosis

Meiosis initiated once in a finite population of cells1 gamete produced / meiosisCompletion of meiosis delayed for months or yearsMeiosis arrested at 1st meiotic prophase andreinitiated in a smaller population of cellsDifferentiation of gamete occurs while diploid infirst meiotic prophaseAll chromosomes exhibit equivalent transcriptionand recombination during meiotic prophase

The Cell - Figure 14.37. Meiosis of vertebrate oocytes

Femalegametogenesis

Polar Bodies

In female gametogenesis only a single (1) haploid egg isproduced from meiosis. In male gametogenesis four (4)haploid sperm are produced from meiosis. So what happens toall the extra DNA in producing this single egg?

Meiosis 1 the "extra" DNA is excluded to the periphery asa 1st polar body, which encloses the extra DNA.Meiosis 2 the "extra" DNA is once again excluded as a2nd polar body. The first polar body may also under gomeiosis 2 producing a 3rd polar body.

These polar bodies are not gametes.Polar bodies have no other function other than to disposeof the extra DNA in oogenesis.Though recent research in mice suggest that oocyte polarbody position may influence fertilization site.

Earlyzygoteshowingpolarbodies

Meiosis Polar Body Movie

Fertilization

Gamete formation, menstrual cycle and fertilisation will also be covered indetail in this week's Laboratory. Fertilization is the complete processresulting in the fusion of haploid gametes, egg and sperm, to form the

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Human uterine tube ciliated epithelium

diploid zygote. The recent development of aided fertilization is describedas in vitro fertilization (in vitro = "in glass", outside the body, IVF).Clinically, all these aided fertilization techniques are grouped as AssistedReproductive Technologies or ART.

Oogenesis - 1 gamete produced/meiosis + 3 polar bodies, meiosis isslow, 1 egg produced and released at ovulationSpermatogenesis - 4 gametes produced/meiosis, meiosis is fast, 200-600 million sperm released at ejaculation

Fertilization Movies

Fertilization Site

Fertilization resulting inembryo development usuallyoccurs in first 1/3 of uterinetube (oviduct, Fallopian tube)The majority of fertilizedoocytes do not go on to form anembryoFertilization can also occuroutside uterine tube associatedwith Assisted ReproductiveTechnology (IVF, GIFT, ZIFT...) and ectopic pregnancyOocyte ovulation - release from the ovary with associated cells, intoperitoneal cavity, uterine tube fimbria then into uterine tube (oviduct,uterine horn, fallopian tube) and epithelial cilia mediated movement.Spermatozoa ejaculation - deposited in vagina, movement of tail to"swim" in uterine secretions through cervix, uterine body and intouterine tube, have approximately 24-48h to fertilize oocyte.

Prior to the fertilization process commencing both the gametes complete of

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Human spermatozoa (light microscope)

a number of biological processes.

Oocyte Meiosis - completes Meiosis 1 and commences Meiosis 2(arrests at Metaphase II).Spermatozoa Capacitation - following release (ejaculation) andmixing with other glandular secretions, activates motility andacrosome preparation.Migration - both oocyte and spermatozoa.

Endocrinology - Diagram of the comparative anatomy of the male andfemale reproductive tracts

Gamete Movement Movies

Fertilization - Male

Spermatozoa: Ejaculation -Capacitation - Spermatozoa motility- Chemotaxis - Binding to zonapellucida - Acrosome reaction -Membrane fusion

Ejaculation

about 3.5 ml, containing 200 -600 million spermatozoaby volume less than 10 %spermatozoaaccessory glands contributemajority of volume (60 % seminal vesicle, 10 % bulbourethral, 30 %prostate)

Male Infertility

Oligospermia (Low Sperm Count) - less than 20 million sperm after

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72 hour abstinence from sexAzoospermia (Absent Sperm) - blockage of duct networkImmotile Cilia Syndrome - lack of sperm motility

Capacitation

spermatozoa activation process - removal of glycoprotein coat andseminal proteins and alteration of sperm mitochondria

Spermatozoa motility

tail of spermatozoa provide movement by microtubulesenergy for this movement is provided by mitochondria in tail initialsegment

Chemotaxis

oocyte cumulus cells release progesterone (may also be other oocyteand follicular fluid factors)

Spermatozoa Binding

Zona pellucida protein ZP2 acts as receptor for spermatozoa binding(species specific)

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Acrosome Reaction

exocytosis of acrosome contents (calcium mediated) MBoC - Figure20-31. The acrosome reaction that occurs when a mammalian spermfertilizes an eggenzymes to digest the zona pellucidaexposes sperm surface proteins to bind ZP2

Membrane fusion

between spermatozoa and oocyte cell membranes, allows sperm nucleipassage into egg cytoplasmmembrane fusion also initiates oocyte processes to block polyspermy

Fertilization - Oocyte

Oocyte: Membrane depolarization - Cortical reaction - Meiosis 2

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Human MII oocyte cortical granules

completion

Membrane Depolarization

caused by spermatozoamembrane fusion, acts asprimary block to polyspermy(fertilisation by more than onespermatozoa)

Cortical Reaction

Inositol triphosphate (IP3) pathway elevates intracellular calcium,exocytosis of cortical granulesenzyme alters ZP2 so it will no longer bind sperm plasma membraneMBoC - Figure 20-32. How the cortical reaction in a mouse egg isthought to prevent additional sperm from entering the egg

Meiosis 2

completion of 2nd meiotic divisionforms second polar body (third polar body may be formed by meioticdivision of the first polar body)

Formation of the Zygote

Early Zygotes

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Human Zygote Mouse Zygote

Pronuclei - Male and Female haploid nuclei approach each other andnuclear membranes break downchromosomal pairing, DNA replicates, first mitotic division

Sperm contributes - centriole which organizes mitotic spindleOocyte contributes - mitochondria (maternally inherited)

Sex Determination

based upon whether an X or Y carrying sperm has fertilized the egg,should be 1.0 sex ratio.actually 1.05, 105 males for every 100 females, some studies showmore males 2+ days after ovulation.cell totipotent (equivalent to a stem cell, can form any tissue of thebody)

Men - Y Chromosome

Y Chromosome carries Sry gene, protein product activates pathwayfor male gonad (covered in genital development)

Women - X Chromosome

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Gene dosage, one X chromosome in each female embryo cell has to beinactivatedprocess is apparently random and therefore 50% of cells have father'sX, 50% have mother's XNote that because men only have 1 X chromosome, if abnormal, thisleads to X-linked diseases more common in male that female wherebothe X's need to be abnormal.

Abnormalities

The most common chromosome abnormality is aneuploidy, the gainor loss of whole chromosomes.

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Caused by meiotic nondisjunction, the failure of chromosomes tocorrectly separate homologues during meiosis I or sister chromatidsduring meiosis II.Down Syndrome - caused by an extra copy of chromosome 21.Trisomy 21 (Down Syndrome)Maternal Age

Chromosomal translocations occur when there is aninappropriate exchange of chromosomal material. PhiladelphiachromosomePhiladelphia chromosome - piece of Chr9 exchanged with Chr22Generates truncated abl, overstimulates cell production, leads tochronic myelogenous leukemia

Hydatidiform Mole

Complete Mole - Only paternal chromosomes (no oocyte nucleuscontribution)Partial Mole - 3 sets of chromosomes ( (triploidy) instead of theusual 2 (2 spermatozoa contribution)

UNSW Embryology Links

spermatozoa oocyte fertilization Trisomy 21 (Down Syndrome)

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Cell Division Links: meiosis | mitosis | Lecture - Cell Division andFertilization | spermatozoa | oocyte | fertilization | zygote | Genetics

References

1. ↑ Bury L, Coelho PA & Glover DM. (2016). From Meiosis to Mitosis:The Astonishing Flexibility of Cell Division Mechanisms in EarlyMammalian Development. Curr. Top. Dev. Biol. , 120, 125-71. PMID:27475851 DOI.

Online Textbooks

Developmental Biology by Gilbert, Scott F. Sunderland (MA):Sinauer Associates, Inc.; c2000Figure 2.9. Summary of meiosis |fusion of egg and sperm plasma membranesMolecular Biology of the Cell 4th ed. Alberts, Bruce; Johnson,Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, PeterNew York and London: Garland Science; c2002 - IV. InternalOrganization of the Cell Chapter 17. The Cell Cycle and ProgrammedCell Death Programmed Cell Death | An Overview of the Cell Cycle |Figure 17-1. The cell cycle | FertilizationMolecular Cell Biology by Lodish, Harvey; Berk, Arnold; Zipursky,S. Lawrence; Matsudaira, Paul; Baltimore, David; Darnell, James E.New York: W. H. Freeman & Co.; c1999 Chapter 13. Regulation of theEukaryotic Cell Cycle Regulation of the Eukaryotic Cell Cycle |Overview of the Cell Cycle and Its Control | Figure 13-2. Currentmodel for regulation of the eukaryotic cell cycle | Movies Proposedalternative mechanisms for chromosome congression. | Centromericattachment of microtubules. | The stages of mitosis and cytokinesis inan animal cell.The Cell - A Molecular Approach by Cooper, Geoffrey M.Sunderland (MA): Sinauer Associates, Inc.; c2000- IV. CellRegulation Chapter 14. The Cell Cycle The Eukaryotic Cell Cycle |

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Figure 14.1. Phases of the cell cycle | Figure 14.32. Comparison ofmeiosis and mitosis | Figure 14.37. Meiosis of vertebrate oocytesHSTAT - In Vitro Fertilization As A Medical Treatment For Male orFemale Infertility

MBoC MBoC - Figure 20-18. Influence of Sry on gonad developmentEndocrinology Endocrinology - Comparative anatomy of male andfemale reproductive tracts

Search

Bookshelf cell division | mitosis | meiosis | fertilization

Pubmed cell division | mitosis | meiosis | fertilization

Reviews

Dennis W Stacey, Masahiro Hitomi Cell cycle studies based uponquantitative image analysis. Cytometry A: 2008, 73(4);270-8 PubMed18163464

Christoph Schorl, John M Sedivy Analysis of cell cycle phases andprogression in cultured mammalian cells. Methods: 2007,41(2);143-50 PubMed 17189856

Terms

Spermatozoa Development

Note there are additional glossaries associated with genital, spermatozoa,oocyte and renal.

acrosome - Cap-shaped cellular structure formed from the golgiapparatus and contains enzymes to dissolve the oocyte (egg) zonapellucida for fertilisation.

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acrosome compaction - Acrosome reshapingprocess in final stages of spermatogenesis(spermatid to spermatozoa).acrosome reaction - Chemical change withinthe spermatozoa following binding to the zonapellucida, only acrosome reacted spermatozoahave an ability to fuse with oocytes.annulus - Cytoskeletal (septin) structure locatedbetween the midpiece and principal piece regionsof the tail, thought to form a diffusion barrierbetween these two domains. PMID 20042538asthenozoospermia - (asthenospermia) Termfor reduced sperm motility and can be the causeof male infertility.axoneme - (axonema) The basic structure incilia and eukaryotic flagella and in thespermatozoa tail, consisting of parallelmicrotubules in a characteristic "9 + 2" pattern.This pattern describes 9 outer microtubule doublets (pairs)surrounding 2 central singlet microtubules, in humans 50 µm long.The motor protein dynenin move the outer microtubules with respectto the central pair, bending the cilia and generating motility. Note thatprokaryotic bacteria have a similar process (flagellum) that uses anentirely different mechanism for motility.blood-testis barrier - (BTB) Formed by tight junctions, basalectoplasmic specializations, desmosome-like junctions and gapjunctions between adjacent Sertoli cells near the basement membraneof the seminiferous epithelium.capacitation - term describing the process by which spermaozoabecome capable of fertilizing an oocyte, requires membrane changes,removal of surface glycoproteins and increased motility.

CatSper - cationic (Ca2+) channel of spermatozoa, progesterone

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activated involved in hyperactivation, acrosome reaction, and possiblychemotaxis.

centriole - a microtubule organising centre. First required foraxoneme formation (distal centriole) that is lost and a second forpronuclei formation (proximal) following fertilisation. Rodents looseboth and only have maternal centrioles.

connecting piece - linkage between the spermatozoa head and themidpiece of the tail. PMID 22767409

cytoplasmic bridges - Transient cytoplasm connections betweenspermatids arising from one spermatogonium due to incompletecytokinesis.

diploid - (Greek, di = double + ploion = vessel) Having two sets ofchromosomes, the normal state for all cells other than the gametes.

end piece - Last portion of the spermatozoa tail region.

fibrous sheath - cytoskeletal structure surrounding the axonemeand outer dense fibers, defining the extent of the principal pieceregion.

haploid - (Greek, haploos = single) Having a single set ofchromosomes as in mature germ/sex cells (oocyte, spermatozoa)following reductive cell division by meiosis. Normally cells are diploid,containing 2 sets of chromosomes.

interstitial cell - (Leydig cell) Male gonad (testis) cell which secretethe androgen testosterone, beginning in the fetus.

Johnsen score - a clinical score (1-10) for assessingspermatogenesis in a human testicular biopsy. Named after the authorof the original article. PMID 5527187

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Leydig cell - (interstitial cell) Male gonad (testis) cell which secretethe androgen testosterone, beginning in the fetus. These cells arenamed after Franz von Leydig (1821 - 1908) a German scientist whohistologically described these cells.meiosis - The cell division that occurs only in production of germcells where there is a reduction in the number of chromosomes(diploid to haploid) which is the basis of sexual reproduction. Allother non-germ cells in the body divide by mitosis.midpiece - (middle piece) spermatozoa tail initial segment ofaxoneme surrounded outer dense fibres then by mitochondria. Nextin the tail is the principal piece then finally the end piece.mitosis - The normal division of all cells, except germ cells, wherechromosome number is maintained (diploid). In germ cell division(oocyte, spermatozoa) meiosis is a modified form of this divisionresulting in reduction in genetic content (haploid). Mitosis, division ofthe nucleus, is followed by cytokinesis the division of the cellcytoplasm and the cytoplasmic contents. cytokinesis overlaps withtelophase.outer dense fibres - (ODF, outer dense fibers) cytoskeletalstructures that surround the axoneme in the middle piece andprincipal piece of the spermatozoa tail.primary spermatocyte - arranged in the seminiferous tubule walldeep (luminal) to the spermatogonia. These large cells enter theprophase of the first meiotic division. (More? Meiosis)principal piece - Spermatozoa tail segment containing the plasmamembrane calcium channels (CatSper1 and CatSper2) required forhyperactivation of motility. Region is partially separated from themidpiece by a barrier called the annulus.Sertoli cells - (sustentacular cell) These cells are the spermatozoasupporting cells, nutritional and mechanical, as well as forming ablood-testis barrier. The cell cytoplasm spans all layers of theseminiferous tubule. The cells are named after Enrico Sertoli (1842 -

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1910), and italian physiologist and histologist.sperm annulus - (Jensen's ring; Latin, annulus = ring) A region ofthe mammalian sperm flagellum connecting the midpiece and theprincipal piece. The annulus is a septin-based structure formed fromSEPT1, 4, 6, 7 and 12. Septins are polymerizing GTPases that can actas a scaffold forming hetero-oligomeric filaments required forcytokinesis and other cell cycle roles.spermatogenesis - (Greek, genesis = origin, creation, generation)The term used to describe the process of diploid spermatagoniadivision and differentiation to form haploid spermatazoa within thetestis (male gonad). The process includes the following cellularchanges: meiosis, reoorganization of DNA, reduction in DNA content,reorganization of cellular organelles, morphological changes (cellshape). The final process of change in cell shape is also calledspermiogenesis.spermatogenesis - (Greek, genesis = origin, creation, generation)The maturation process of the already haploid spermatazoa into themature sperm shape and organization. This process involvesreorganization of cellular organelles (endoplasmic reticulum, golgiapparatus, mitochondria), cytoskeletal changes (microtubuleorganization) and morphological changes (cell shape, acrosome andtail formation).spermatogonia - The cells located in the seminiferous tubuleadjacent to the basal membrane that either divide and separate torenew the stem cell population, or they divide and stay together as apair (Apr spermatogonia) connected by an intercellular cytoplasmicbridge to differentiate and eventually form spermatazoa.spermatozoa head - Following spermiogenesis, the first region ofthe spermatozoa containing the haploid nucleus and acrosome. Inhumans, it is a flattened structure (5 µm long by 3 µm wide) with theposterior part of nuclear membrane forming the basal plate region.The human spermatozoa is about 60 µm long, actively motile and

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divided into 3 main regions (head, neck and spermatozoa tail).spermatozoa neck - Following spermiogenesis, the second regionof the spermatozoa attached to basal plate, transverse orientedcentriole, contains nine segmented columns of fibrous material,continue as outer dense fibres in tail. In humans, it forms a shortstructure (1 µm). The human spermatozoa is about 60 µm long,actively motile and divided into 3 main regions (head, neck and tail).spermatozoa tail - Following spermiogenesis, the third region ofthe spermatozoa that has a head, neck and tail). The tail is alsodivided into 3 structural regions a middle piece, a principal piece andan end piece. In humans: the middle piece (5 µm long) is formed byaxonema and dense fibres surrounded by mitochondria; the principalpiece (45 µm long) fibrous sheath interconnected by regularly spacedcircumferential hoops; the final end piece (5 µm long) has an axonemasurrounded by small amount of cytoplasm and plasma membrane.spermatogonial stem cells - (SSCs) The spermatagonia cellslocated beside the seminiferous tubule basal membrane that eitherdivide and separate to renew the stem cell population, or they divideand stay together as a pair (|Apr spermatogonia) connected by anintercellular cytoplasmic bridge to differentiate and eventually formspermatazoa.spermatozoon - singular form of of spermatozoa.sperm protein 56 - A component of the spermatozoa acrosomalmatrix released to the sperm surface during capacitation.teratospermia - Clinical term for a spermatozoa with abnormalmorphology (small, large, defects in the head, tail, and/or mid-piece)present in the semen or ejaculate.

See also: Spermatozoa Terms collapse table

Other Terms Lists

External Links

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External Links Notice - The dynamic nature of the internet may meanthat some of these listed links may no longer function. If the link no longerworks search the web with the link text or name. Links to any externalcommercial sites are provided for information purposes only andshould never be considered an endorsement. UNSW Embryology isprovided as an educational resource with no clinical information orcommercial affiliation.

McGraw-Hill Animation comparing Mitosis and MeiosisSalmon Lab Mitosis Movies

2018 ANAT2341 - Timetable | Course Outline | Group Projects | Moodle |Tutorial 1 | Tutorial 2 | Tutorial 3

Labs: 1 Preimplantation and Implantation | 2 Reproductive TechnologyRevolution | 3 Group Projects | 4 GM manipulation mouse embryos | 5 Earlychicken eggs | 6 Female reproductive tract | 7 Skin regeneration | 8Vertebral development | 9 Organogenesis Lab | 10 Cardiac development | 11Group projects | 12 Stem Cell Journal Club

Lectures: 1 Introduction | 2 Fertilization | 3 Week 1/2 | 4 Week 3 | 5Ectoderm | 6 Placenta | 7 Mesoderm | 8 Endoderm | 9 Research Technology| 10 Cardiovascular | 11 Respiratory | 12 Neural crest | 13 Head | 14Musculoskeletal | 15 Limb | 16 Renal | 17 Genital | 18 Endocrine | 19 Sensory| 20 Fetal | 21 Integumentary | 22 Birth | 23 Stem cells | 24 Revision

Student Projects:

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© Dr Mark Hill 2018, UNSW Embryology ISBN: 978 0 7334 26094 - UNSW CRICOS Provider Code No. 00098G