GametogenesisMitosis and MeiosisCell Division
Todays ObjectivesIdentify the meiotic& mitotic process
Identify the important components of the process of GAMETOGENESIS
Spermatogenesis
Gametogenesis in Mammals creating mature functioning gametes
Oogenesis
Process of producing complete motile spermatozoa from spermatogonia. Occurs in seminiferous tubules of the testes Process of producing mature oocytes from oogonia Occurs in ovaries
Gametogenesis:Process of creating mature functioning gametes1- Reduce the number of chromosomes to 1/2 of somatic cells (this is done by meiotic or maturation division).
2- Alter the shape of the germ cell in preparation forfertilization; -The cytoplasm is increased in the ovum to provide sufficient nutrition for the dividing zygote. -The cytoplasm is decreased in the sperm + it develops head, neck, body and tail
Nucleus DNA: arranged in chromosomes (network of granules = nuclear chromatin) RNA: spherical intranuclear structure(s) - nucleolus / nucleoli
ChromatinIn the interphase nucleus the staining area with homogeneous electron-density is called euchromatin .The dense staining area with higher electron-density is called heterochromatin.
Nucleolus
It is located in nucleus, without membrane coat. It is with rather high electron-density structure. It is the sites of ribosomal RNA synthesis and ribosome assembly.
Terminology Chromatin - thin fibrous form of DNA and proteins has beaded appearance
Anatomy of a Chromosome Centromere point where sister chromatids are joined together =short arm; upward =long arm; downward Telomere-tips of
centromere
chromatids
telomere
Chromosomes Homologous Chromosome: The two chromosomes of a matching pair
Terminology Diploid - two sets of chromosomes (2n), in humans 23 pairs or 46 total Haploid - one set of chromosomes (n) - gametes or sex cells, in humans 23 chromosomes
Why Do Cells Divide?For growth, repair, and reproduction
Cell Division vs. Nuclear Division Cytokinesis: The actual division of the cell into two new cells.
Mitosis: The division of the nucleus of the cell into two new nuclei. Note: Sometimes cells go through mitosis without going through cytokinesis. Describe a cell that did this.
Getting ready to split Cell cycle has two parts: growth and preparation (interphase) cell division mitosis (nuclear division) cytokinesis (cytoplasm division)
Paired chromosomes Before mitosis, the DNA chains duplicate to form new chromosome material. The duplicated chromosomes lie side by side = chromatid. Mitosis = the process by which chromatids separate into chromosomes.
Chromatids
Interphase Occurs between divisions
The Cell Cycle The sequence of growth and division of a cell. 95% of cell cycle in interphase 5% of cell cycle in mitosis
Interphase Growth Stage (G1) metabolic activity of the cell Synthesis Stage (S) metabolic activity of the cell, replication of DNA Growth Stage 2 (G2) metabolic activity of the cell, prepare for division
Mitosis Interphase: DNA duplication to form chromatids just before mitosis Prophase: centriole migration, mitotic spindle Metaphase: chromosomes line up in centre, chromatids still joined at centromere Anaphase: chromatids separate into chromosomes Telophase: new nuclear membranes form, cytoplasm divides
Prophase Chromosome condense Microtubles form The nuclear envelope breaks down
prometaphaseNuclear membrane is degraded (disappeared) Microtubules entered nuclear space
Metaphase
Chromosomes are pulled to center of cell Line up along metaphase plate
Anaphase
Centromeres divide Spindle fibers pull one set of chromosomes to each pole Precise alignment is critical to division
Telophase Nuclear envelope form around chromosomes Cytokinesis
Interphase Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis
IPPMATC
I Pay Pounds More At The Costa
Meiosis
What is Meiosis?A division of the nucleus that reduces chromosome number by half. Important in sexual reproduction Involves combining the genetic information of one parent with that of the the other parent to produce a genetically distinct individual
Phases of Meiosis A diploid cell replicates its chromosomes Two stages of meiosis Meiosis I and Meiosis II Only 1 replication
Synapsis - pairing of homologous chromosomes forming a tetrad. Crossing over chromatids of tetrad exchange parts.
Produce 4 haploid gametes through - Interphase replication of DNA - Meiosis I separation of (reduction) homologous chromosomes(in 4-5 steps: prophase I, metaphase I, anaphase I, and telophase I and cytokinesis I)
Meiosis
- Meiosis II ( similar mitosis) separation of sister chromatids(prophase II, metaphase II, anaphase II, telophase II and cytokinesis II)
Only occurs in gonads
Meiosis InterphaseMeiosis is preceded by interphase.
Meiosis InterphaseThe chromosomes have replicated, and the chromatin begins to condense.
Meiosis Prophase IThe chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one anotherEach pair contains four sister chromatids - tetrad
Meiosis Metaphase IThe nuclear membrane dissolves and the homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles.
Meiosis Anaphase IThe chromosomes move to opposite ends of the cell.
Meiosis Telophase I & CytokinesisThe cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes.
Meiosis Prophase IIThe cell has divided into two daughter cells.
Meiosis Metaphase IIAs in Meiosis I, the chromosomes line up on the spindle fibers.
http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/m eiosis1.html
Meiosis Anaphase IIThe two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell.
Telophase II & CytokinesisWith the formation of four cells, meiosis is over. Each of these prospective germ cells carries half the number of chromosomes of somatic cells.
While a tetrad is present, crossing over occurs Which involves the genes of one chromatid are exchanged for the genes of another. This gives rise to genetic variability.
Crossing over
exchange
Both are forms of nuclear division Both involve replication Both involve disappearance of the nucleus, and nucleolus, nuclear membrane Both involve formation of spindle fibers
Review Mitosis & Meiosis
Meiosis produces daughter cells that have 1/2 the number of chromosomes as the parent. Go from 2n to 1n. Daughter cells produced by meiosis are not genetically identical to one another. In meiosis cell division takes place twice but replication occurs only once.
DIFFERENCES
Meiosis produces daughter cells that have 1/2 the number of chromosomes as the parent. Go from 2n to 1n. Daughter cells produced by meiosis are not genetically identical to one another. In meiosis cell division takes place twice but replication occurs only once.
DIFFERENCES
Gametogenesis in Mammals Spermatogenesis Process of producing complete motile spermatozoa from spermatogonia. Occurs in seminiferous tubules of the testes Process of producing mature oocytes from oogonia Occurs in ovaries
Oogenesis
Gametogenesis:Process of creating mature functioning gametes1- Reduce the number of chromosomes to 1/2 of somatic cells (this is done by meiotic or maturation division).
2- Alter the shape of the germ cell in preparation forfertilization; -The cytoplasm is increased in the ovum to provide sufficient nutrition for the dividing zygote. -The cytoplasm is decreased in the sperm + it develops head, neck ,body and tail
Spermatogenesis Start: it starts after puberty and continues into old age. Duration: It takes about 60-64 days (including the process of spermio-genesis) Site in the seminiferous tubules of the testis.
Steps: It passes in 4 stages: 1. Stage of proliferation:: 2 Stage of growth:
3. Stage of maturation: by 2 stages of divisions:A-First meiotic division: 1ry spermatocyte divides by meiosis to form two 2ry spermatocytes (23 chromosomes). B-Second meiotic division: each secondary spermatocyte divides by mitosis to form two spermatids (23chromosomes).
4-Stage of transformation spermio-genesis= change in shape with no further division , spermatids change to motile sperms:
Nuclear condensation: thickening and reduction of the nuclear size, condensation of the nuclear contents into the smallest space. Acrosome formation: Forming a cap (acrosome) containing enzymes that play an important role in the penetration through the pellucid zone of the oocyte. Flagellum formation: generation of the sperm cell tail. Cytoplasma reduction: elimination of all unnecessary cytoplasm
Structure of sperm
Abnormalities
*Necrospermia: dead sperms in the ejaculate. *Oligospermia: sperm count is below normal. *Azospermia: Complete absence of sperms in the semen.
ICSI Intracytoplasmatic sperm injection
In vitro fertilisation (IVF)
OogenesisChanges that take place in the ovary during which the oogonia cells (primordial female germ cells) differentiate into mature oocyte (ready for fertilization). *Start: from 3rd month of intrauterine life till
birth, then continues after puberty (during eachovarian cycle), and after fertilization & end at menopause. *Site: in the ovary.
1-proliferation 2-growth
OMIOocyte maturation inhibitor
At puberty
flex
25 m
0.15 to 0.2 mm
Sex determination The sex of a child is always determined by the sperm of the father. Any presence of a Y chromosome makes the person a male. The mothers eggs always carry an X chromosome. If the sperm that fertilizes the egg carries an X chromosome, the child will be a girl and if it carries a Y chromosome the child will be a boy. Girl=XX Boy=XY
Down syndrome: chromosome 21
trisomy of
Trisomy-18
FEMALE REPRODUCTIVE CYCLES
females undergo reproductive cycles in the ovaries and uterus every 28 days Most females begin menstruation between 10-15 As with males, many hormonal changes are occurring, so the body may take a couple of years to adjust Cycle may be irregularMenopause Ceasing of menstruation Between 45-50n
Hormones control the cycle FSH & LH (secreted by pituitary gland) and estrogen & progesterone (secreted by the ovary Nutrition, stress & diet can influence cycle
NORMAL MENSTRUAL CYCLEWhat regulate the phases of the MC & ovulation? Interaction between hypothalamus, pituitary & ovariesWhat is the mean age of menarche & menopause? Menarche 12.7 Menopause 51.4
IV) Female Reproductive System C) Menstrual Cycle the menstrual cycle includes: oogenesis, ovulation, thickening and shedding of the endometrium
Two distinct cyclesOvarian cycle: Uterine cycle
1) Ovarian cycle:At puberty, under the influence of FSH, a number of 1ry oocytes begin to mature with each ovarian cycle, however,usually, only one primary follicle develops into a mature follicle & ruptures through the surface of the ovary to expel the oocyte
PHASES OF THE OVARIAN CYCLE1-Follicular phase (14 days): 2-Luteal phase (post ovulatory phase, 14 days)
1-FOLLICULAR PHASE:MATURATION OF THE FOLLICLE (FOLLICULOGENESISon day 1 of the menstrual cycle & ends with ovulation RECRUITMENT FSH maturation of a group of ovarian follicles recruitment only one reaches maturity
(stratum granulosum),
Sheath
Graafian F. corona radiata crowncumulus ovaricus (cumulus oophorus
1-Follicular phase (14 days)
2-Luteal phase (post ovulatory phase, 14 days):
-It follows ovulation and leads to the formation of corpus luteum under the effect of luteinizing hormone (LH) . The corpus luteum will secrete progestrone hormone (which is responsible for the secretory stage of uterine cycle)
OVULATIONThe dominant follicle bulges from the ovarian cortex Gentle release of the oocyte surrounded by the cumulus granulosa cells on the 14th day of menstrual cycle.
Mechanism of follicular rupture: 1-Mechanical factor by the increasing of follicle size & its squeezing effect on the capsule of the ovary2- Follicular pressure Changes in composition of the antral fluid colloid osmotic pressure 3-Enzymatic rupture of the follicular wall LH & FSH granulosa cells production of plasminogen activator plasmin fibrinolytic activity breake down of F. wall
1- Plasma membrane (Oolemma): Innermost layer. 2- Vitelline membrane: Attached to plasma membrane. 3- Zona pellucida: Transparent non-cellular layer found outer to the Vitelline membrane. 4- Corona radiata: Outer layer formed of follicle cells. These cells are found together by hyaluronic acid
MENSTRUATION Periodic desquamation of the endometrium Just before menses the endometrium is infiltrated with leucocytes Prostaglandins are maximal in the endometrium just before menses Prostaglandins constriction of the spiral arterioles ischemia & desquamation Followed by arteriolar relaxation, bleeding & tissue breakdown
2) Uterine cycle: 1-Stage of menstruation: Flow phase (bleeding) 2-Stage of repair: 3-Stage of proliferation: 4-stage of secretion
5-10 1-5
PREMENSTRUAL SYNDROME (PMS)Variety of symptoms that some females experience Occurs before the menstrual period Some females never experience PMS
Symptoms Nervous tension, anxiety, irritability, Bloating, weight gain, depression/mood swings, fatigue
PMS cont Causes arent completely understood More common in 30s women Related to hormone imbalance Nutritional deficiency
Treatment Change in diet & exercise Serious cases = antidepressant meds