gametogenesis
TRANSCRIPT
SEX CELL DIFFERENTIATION
OOGENESIS – EGG DIFFERENTIATION
SPERMATOGENESIS – SPERM DIFF.
◦ SPERMIOGENESIS – TRANSFORMATION OF THE MALE GAMETE
IN MAN/MAMMALS, PRIMORDIAL GERM CELL COMES FROM YOLK SAC ENTODERM NEAR CAUDAL END OF BODY
FROM THERE THEY MIGRATE FORWARD THROUGH THE MESENCHYME OF THE MESENTERY AND INTO THE GENITAL RIDGE WHICH SOON BECOMES THE SEX GLAND
THEN PROLIFERATION
PROLIFERATION IS PERIODIC (MONTHLY IN FEMALES) URING THE POTENTIAL CHILD-BEARING YEARS
CELL PROLIFERATION – PRIMITIVE CELL REPEATEDLY DIVIDES
PERIOD OF GROWTH – RAPID ENLARGEMENT OF THE CELLS PRODUCED
PERIOD OF MATURATION – NUCLEAR CHANGES LIMITED TO THE FINAL TWO DIVISIONS
ORIGIN OF THE FOLLICLES
◦ PRIMORDIAL CELLS (OOGONIA) PROLIFERATE WITHIN THE CORTEX OF THE OVARY
◦ SMALLER EPITH. CELLS, OF GERMINAL-EPITH ORIGIN ENCASED THE OOGONIA AND PRODUCED PRIMARY FOLLICLE
◦ AFTER BIRTH, FORMATION OF HUMAN OOGONIA STOPS THEN CELLS ARE NOW CALLED OOCYTES
370,000 – AT BIRTH
190,000 – AT PUBERTY
26,000 – AT AGE 30
AFTER 30 OR MORE YEARS (CHILD-BEARING SPAN), FOLLICLES WILL NO LONGER BE SEEN
NO ADVANCE BEYOND THE STAGE OF THE PRIMARY FOLLICLE UNTIL PUBERTY (14TH YEAR)
FEW HUNDREDS OF OOCYTES ARE LIBERATED PERIODICALLY DURING OVULATION
GROWTH OF FOLLICLE STARTS SLOWLY BUT GROWS RAPIDLY 1-3 DAYS PRIOR TO RUPTURE
MATURATION – ACHIEVED BY MEIOSIS WITH 4 CELLS HAVING EQUAL NUCLEI WHILE THE CYTOPLASM IS UNEQUALLY DIVIDED
1 LARGE RIPE OVUM 3 RUDIMENTARY OVA (POLAR BODIES) OR
POLOCYTES CYTOPLASM – GRANULAR AND
CONTAINS FEW TO MANY INERT GRANULES
YOLK/DEUTOPLASM – MADE UP OF FATTY AND ALBUMINOUS SUBSTANCE; SERVES AS NOURISHMENT FOR THE EMBRYO
YOLK – USEFUL IN CLASSIFYING EGGS.
I. BASED ON RELATIVE ABUNDANCE OF YOLK:
1. SMALL
2. MEDIUM
3. LARGE
II. DISTRIBUTION OF YOLK IN CELLS:
1. ISOLECITHAL – EQUAL YOLK
MEIOLECITHAL – LITTLE YOLK
- INVERTEBRATES
- ALL MAMALS EXCEPT LOWEST FORMS
2. TELOLECITHAL EGGS – ABUNDANT YOLK AND CONCENTRATED IN ONE HEMISPHERE
-INVERTEBRATES
-ALL VERTEBRATES LOWER THAN MARSUPIALS
- CHICK EGG
3. MEDIALECITHAL (MEDIUM YOLK) –MODERATE YOLK – AMPHIBIANS
4. MEGALECITHAL- LARGE, YOLK RICH EGGS OF BONY FISHES , REPTILES , BIRDS
5. CENTROLECITHAL- DISTINCTIVE ARRANGEMENT OF YOLK, MASSED CENTRALLY BUT SORROUNDED BY A PERIPHERAL SHELL OF CLEAR CYTOPLASM.
EGG POLARITY:
ANIMAL POLE – SITE WHERE POLAR BODIES PINCH OFF
- VIGOROUS PART IN DEVT. & WHERE HIGHEST CAPACITY FOR ACTIVITY RESTS
- VEGETAL POLE- SLUGGISH END OF CELL AND CONCERNED WITH THE DEVT. OF NUTRITIVE ORGANS
- YOLK LADEN
PROTECTIVE MEMBRANES:
1° MEMBRANE-CELL/PLASMA MEMBRANE
2° MEMBRANE- ZONA PELLUCIDA
3° MEMBRANE –ADDED BY THE OVIDUCT
AS THE EGG PASSES THROUGH IT
- JELLY OF FROG’S EGGS
- ALBUMEN OF RABBIT’S EGG
- ALBUMEN AND SHELL OF HEN’S EGG
CELLULAR CORDS ( GERMINAL EPITHELIUM)
TESTES TUBULES
SPERMATOGONIA (STEM CELLS)- LARGER
INDIFFERENT CELLS- SMALLER
PUBERTY – SOME SPERMATOGONIA REMAIN AS STEM CELLS WHILE OTHERS BECOME PRIMARY SPERMATOCYTE-2°SPERMATOCYTE-SPERMATID-SPERM
DETACHED FROM SERTOLI CELLS AND ARE SET FREE INSIDE THE SEMINIFEROUS TUBULES
SPERM CELL- SMALLEST CELL IN MASS MADE UP OF HEAD, NECK & TAIL.
AT THE END OF MATURATION (MEIOSIS)
THE DEVT. OF EGG IS COMPLETE AND THE EGG BECOMES FUNCTIONAL WHILE THE MALE GAMETE UNDERGOES A SERIES OF TRANSFORMATIONS BEFORE A FUNCTIONAL SPERM CELL IS DERIVED
CHROMOSOME NUMBERS
(2N) MAN=46 (DIPLOID CHROMOSOME#)
(N) MAN=23 (HAPLOID CHROMOSOME#)
FEMALE -22 ORDINARY CHROMOSOME PAIR
-23RD PAIR(SEX CHROMOSOME)
(XX) PAIR
MALE
22 ORDINARY CHROMOSOME PAIR
23RD PAIR (XY) PAIR
24 DIFFERENT KINDS OF CHROMOSOMES
COMPARISON OF EGG & SPERM OF ANIMALS IN GENERAL
FEATURES OVUM SPERMATO-ZOON
SIZE LARGE SMALL
SHAPE SPHEROIDAL ELONGATED
QUANTITY FEW (ONE) OFTEN IN MILLIONS
MOTILITY NON-MOTILE VIGOROUS(FLAGELLATE)
PROTECTION EGG ENVELOPES
NONE
CYTOPLASM BULKY MINIMAL
YOLK LITTLE TO MUCH
NONE
CENTRO-SOME
DISAPPEARS RETAINED –CENTRIOLE &
AXIAL FILAMENT
MITOCHON-DRIA
DIFFUSED IN THE BODY ONLY
GOLGI-APPARATUS
DIFFUSED IN ACROSOME
ONLY
NUCLEUS OPEN STRUCTURED
CONDENSED AS SPERM
HEAD
NUCLEOLUS TYPICAL INDISTINGUISHABLE
SEX DETERMININ
G ROLE
RARELY TWO KINDS(MOTH
S/BIRDS)
USUALLY TWO
KINDS(MALE&FEMALE)
INTERNAL FERTILIZATION
-SMALL NUMBER OF EGGS
EXTERNAL FERTILIZATION
-LARGE VOLUME OF EGGS
TYPES OF BREEDING:
• CONTINUOUS-ALL THOUGHOUT THE YEAR
• SEASONAL/ANNUAL SPAWNING PERIOD
• SPONTANEOUS- SEXUAL EXCITEMENT/PERIOD OF HEAT / ESTRUS
• PROVOKED OVULATION- INDUCED BY THE ACT OF COPULATION.
• PERIODIC (INTERVALS OF 4 WEEKS) SPONTANEOUS
HUMAN FEMALE
-OVULATION (14 YRS.) + 30 YEARS OF SEXUAL ACTIVITY
FOLLICLE RUPTURE- SIMILAR TO THE RUPTURE OF A BOIL; TAKES PLACE AT THE STIGMA
- HORMONAL FACTOR AND LOCAL WEAKENING OF FOLLICULAR WALL
EGG TRANSPORT- MADE POSSIBLE BY HORMONAL CONTROL AND OVARY ACTIVITY.
TIME OF OVULATION- MIDDLE OF THE CYCLE
28-DAY CYCLE
26-DAY CYCLE
30-DAY CYCLE
EGG VIABILITY- FERTILIZABLE PERIOD IS LESS THAN ONE DAY – GENERATION TAKES PLACE
CORPUS LUTEUM- OVARIAN STRUCTURE (COLLAPSED & FOLDED) VESICULAR
FOLLICLE- MADE UP OF LUTEIN CELLS• CORPUS LUTEUM OF OVULATION• CORPUS LUTUEM OF PREGNANCY• CORPUS ALBICANS- WHITE SCAR LEFT
MADE UP OF FIBROUS TISSUE.
• PSEUDOCOPULATION- INCREASES CERTAINTY OF UNION
• COPULATION- SEXUAL EMBRACESPERM STORAGE- ACCUMULATION AT
EPIDIDYMIS(TRAVERSED IN 12 DAYS)SPERM DISCHARGE- EJACULATION(MALE
CLIMAX DURING COITUS) SEMEN (SPERMATOZOA PLUS THE
SECRETIONS FROM 3 ACCESSORY GLANDS:
• SEMINAL VESICLE
• BULBO-URETHRAL GLAND
• PROSTATE GLAND
3 ML EJACULATE-250,000,000 SPERMS
SPERM TRANSPORT-LASHING, FLAGELLATED MOVEMENT ; WILL TRAVERSE UTERUS IN 70 MIN.(7 INCHES)
SPERM VIABILITY= 1-2 DAYS
IN VITRO- TWO WEEKS
HUMAN SEMEN(FROZEN IN GLYCEROL
AT - 70℃ (CAN SURVIVE FOR MANY MONTHS
PROCESS WHEREBY 2 GAMETES FUSE TOGETHER TO CREATE A NEW INDIVIDUAL WITH A GENOME DERIVED FROM BOTH PARENTS
ACCOMPLISHES 2 SEPARATE ENDS; SEX (THE COMBINING OF GENES DERIVED FROM 2 PARENTS) AND REPRODUCTION (THE CREATION OF A NEW ORGANISM)
CONCEPTION CONSISTS OF 4 MAJOR EVENTS:
1. CONTACT AND RECOGNITION BETWEEN SPERM AND EGG. THIS ENSURES THAT THE SPERM AND EGG ARE OF THE SAME SPECIES
2. REGULATION OF SPERM ENTRY INTO THE EGG. ONLY ONE SPERM CAN ULTIMATELY FERTILIZE THE EGG. THIS IS USUALLY ACCOMPLISHED BY ALLOWING ONLY ONE SPERM TO ENTER THE EGG AND INHIBITING ANY OTHERS FROM ENTERING
3. FUSION OF THE GENETIC MATERIAL OF SPERM AND EGG
4. ACTIVATION OF EGG METABOLISM TO START DEVELOPMENT
ANTON VAN LEEUWENHOEK – CO-DISCOVERER OF SPERM
NICOLAS HARTSOEKER – CO-DISCOVERER OF SPERM
DREW A PICTURE OF A PREFORMED HUMAN (HOMUNCULUS)
BELIEF THAT THE SPERM CONTAINED THE ENTIRE EMBRYONIC ORGANISM
POOLING TOGETHER OF SPERM AND EGG NUCLEI
• INVERTEBRATES ( ROTIFERS, CRUSTACEANS INSECTS) DEVELOP WITHOUT THE BENEFIT OF FERTILIZATION(PARTHENOGENESIS)
RESULTS OF FERTILIZATON:
1. REASSOCIATION OF MALE AND FEMALE SETS OF CHROMOSOMES , RESTORING THEM TO THE FULL DIPLOID NUMBER.
2. SEX DETERMINATION
3. ACTIVATION OF OVUM INTO CELL DIVISION OR CLEAVAGE.
SEX DETERMINATION – IS ESTABLISHED AT THE TIME OF FERTILIZATION
DURING MEIOSIS, CHROMOSOME NUMBER IS HALVED
22+X – FEMALE
22+X – MALE; 22+Y – MALE
22+X + 22+X = 44+2X
22+X + 22+Y = 44+X+Y
PERIODS OF EARLY DEVELOPMENT:
1) GAMETOGENESIS
2) FERTILIZATION
3) CLEAVAGE
4) GASTRULATION
FERTILIZED EGG-MANY CELLED INDIVIDUAL(CLEAVAGE) - CELLS TYPICALLY ARRANGE THEMSELVES INTO A HOLLOW SPHERE, THE BLASTULA
CELLS OF BLASTULA- REDISTRIBUTED AS THE PRIMARY GERM LAYERS(GASTULATION)
IT CONTAIN THE MATERIAL OUT OF WHICH THE EMBRYO AND ALL ITS PARTS WILL DIFFERENTIATE.
• ECTO
• MESO
• ENTO/ENDODERM
THE VERTEBRATE GROUPS
I. ANAMNIOTA- WITHOUT AMNION
FISHES-LAMPREY , STURGEON,SHARK,BONY FISHES
AMPHIBIANS-FROGS,TOAD,SALAMANDERS
II. AMNIOTA- WITH AMNION
REPTILES
-LIZARD,CROCODILES,SNAKES,TURTLES
MAMMALS – HAIR AND MAMMARY GLANDS
• MONOTREMES- DUCK-BILL /ECHIDNA• MARSUPIALS-OPOSSUM/ KANGAROO• PLACENTALS-YOUNG NOURISHED IN THE
UTERUS VIA PLACENTA • PRIMATES- WITH NAILS
(LEMUR,MONKEY,APE AND MAN) –SUBORDER ANTHROPOIDA
-DOUBLING/FRACTIONATING PROCESS PRODUCING COHERING,STICKY, BLASTOMERES ARRANGED AROUND A CENTRAL,FREE SPACE(BLASTOCOELE)
EGG CLASSIFICATION ON THE BASIS OF ABUNDANCE AND YOLK DISTRIBUTION:
A. TOTAL- HOLOBLASTIC OVA; ENTIRE OVUM DIVIDES
1. EQUAL-ISOLECITHAL OVA
-EQUAL SIZED BLASTOMERES
• AMPHIOXUS/MARSUPIAL/PLACENTAL MAMMALS
2. UNEQUAL- MODERATELY TELOLECITHAL OVA
• LOWER FISHES / AMPHIBIANS
B. PARTIAL- MEROBLASTIC OVA; ONLY PROTOPLASMIC REGION DIVIDES.
1. DISCOIDAL-HIGHLY TELOLECITHAL OVA
-MITOSIS RESTRICTED TO THE ANIMAL POLE.
• HIGHER FISHES/REPTILES/BIRDS/
MONOTREME MAMMALS
2. SUPERFICIAL – CENTROLECITHAL OVA; DIVISION RESTRICTED TO THE PERIPHERAL CYTOPLASMIC INVESTMENT
• ARTHROPODS
AMPHIOXUS-FISH-SHAPED; LOW CHORDATE
AMPHIBIANS REPTILES/ BIRDS MAMMALS
- FISH SHAPED; LOW CHORDATE
- EARLY STAGES OF DEVT. IS SIMILAR TO SOME INVERTEBRATES
- ISOLECITHAL EGGS
- CLEAVAGE IS TOTAL AND NEARLY EQUAL
- SUBSEQUENT CELL DIVISIONS IN ALTERNATE PLANES PRODUCES 32,64 ANO 128 CELL STAGES
- SIZE OF CELLS ARE PROGRESSIVELY DIMINISHED WHILE THE CENTRAL CAVITY ENLARGES TO FORM THE BLASTOCOELE
MODERATELY TELOLECITHAL (FAIR AMOUNT OF YOLK)
- CLEAVAGE IS TOTAL BUT UNEQUAL
- UPPER 4 MICROMERES ARE SMALLER THAN THE LOWER 4
- FORMS A CENTRAL BLASTOCOELE WHERE BLASTOMERES AT THE ANIMAL POLE ARE SMALLER; LARGER & FEWER AT VEGETAL POLE
WALL IS MORE THAN 1 CELL THICK
BLASTOCOELE IS RELATIVELY SMALL; LOCATED ABOVE CENTER DUE TO THE THICK WALL OF THE VEGETAL POLE
WITH LARGE EGGS
- CLEAVAGE IS PARTIAL & DISCOIDAL
- PRODUCES A DISCOIDAL PLATE OF CELLS PERCHED ON THE SURFACE OF THE YOLK AND SEPERATED FROM IT BY A CLEFT
- CLEAVAGE PRODUCES A MODIFIED BLASTULA( DISCOBLASTULA) WITH THE CELLULAR CAP CALLED A BLASTOCOELE
MARSUPIAL & PLACENTAL MAMMALS HAVE EMBRYOS THAT ARE DEVELOPED WITH DEPENDENCE ON THE MOTHER.
- EGGS ARE ISOLECITHAL- CLEAVAGE TAKES PLACE IN THE ZONA
PELLUCIDA & THE BLASTOMERES ACCOMMODATE THEMSELVES TO THE SPHEROIDAL CAVITY.
- CLEAVAGE IS TOTAL AND NEARLY EQUAL/
- DIVISION BEGINS IN THE UTERINE TUBE & COMPLETED IN THE UTERUS
- COMPLETED WITHIN A RANGE OF 70 HRS.(RABBIT) TO 190 HRS. FOR THE COW.
INVOLUTION , ELONGATION & CONVERGENCE
- CHARACTERIZE GASTRULATION IN ALL CHORDATES
ANIMAL TYPE
TYPE OF EGG
CLEA-VAGE
BLAS-TULA
BLASTU-LA CAVITY
METHODS OF GASTRULATION
COMMENT ON GASTRULATION
AMPHIOXUS
ISOLECITHAL (LITTLEYOLK)
TOTAL;EQUAL
SPHERE;WALL A SINGLE LAYER
SPHERI-CAL RELATIVELY LARGE
INVAGI-NATION; INVOLU-TION VIA BLASTO-PORE
EARLY INNER LAYER IS A COMPO-SITE
AMPHI-BIANS
TELOLE-CITHAL(MODE-RATE YOLK)
TOTAL;UNEQUAL
SPHERE; WALL LAYERED;THICK-NESS VARIES
SPHERI-CAL; RELATIVELY SMALL;ECCEN-TRIC
CHIEFLY IN VOLU-TION VIA BLASTO-PORE
INVOLU-TED LAYERS ARE SEPARA-TE FROM START
BIRDS TELOLE-CITHAL(MASSIVE YOLK)
PARTIAL;DISCOI-DAL
CELL-DISC;BLASTO-DERM)LIES ON MASSIVE YOLK
SHA-LLOW;DELAYED UNTIL ENTO-DERM FORMS
DELAMI-NATION;INVOLU-TION VIA PRIMI-TIVE STREAK
OCCURS IN TWO STAGES;MODI-FIEDAMPHIBIAN STYLE
MAMALS(EXCEPTLOWEST)
ISOLECI-THAL(LITTLE YOLK)
TOTAL;EQUAL
BLASTO-CYST, WITH INNER CELL MASS
MERGEDWITH YOLK-FREE BLASTOCYST CAVITY
DELAMINATION;INVOLU-TION VIA PRIMI-TIVE STREAK
OCCURS IN TWO STAGES;BASICA-LLYSIMILAR TO BIRDS
ECTODERM MESODERM(INCLUDING
MESENCHYME)
ENTODERM
1. EPIDERMIS,INCLUDING: CUTANEOUS GLANDS HAIR, NAILS &LENS
2. EPITHELIUM OF: SENSE ORGANS. NASAL CAVITY;SINUSES.MOUTH , INCLUDING: ORAL GLANDS; ENAMEL,
1. MUSCLE(ALL TYPES)
2. CONNECTIVE TISSUE ; CARTILAGE;BONE;NOTOCHORD
3. BLOOD;BONEARROW
4. LYMPHOID TISSUE.
EPITHELIUM OF:5.BLOOD VESSELS;
LYMPHATICS.
EPITHELIUM OF:1. PHARYNX,INCLU
DING: ROOT OF TONGUE , AUDITORY TUBE, ETC. TONSILS; THYROID PARATHYROIDS ; THYMUS
2. LARYNX; TRACHEA; LUNGS
3. NERVOUS TISSUE , INCLUDING; HYPOPHYSIS,CHROMAFFIN TISSUE
6. BODY CAVITIES
7.KIDNEY; URETER
8.GONADS; GENITAL DUCTS
9.SUPRARENAL10.JOINT
CAVITIES , ETC
3.DIGESTIVETUBE , INCLUDING : ASSOCIATED GLANDS4.BLADDER5.VAGINA(ALL?),VESTIBULE.6.URETHRA , INCLUDING: ASSOCIATED GLANDS.