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42 Cards in this Set
- Front
- Back
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Gametogenesis |
Production of haploid gametes, spermatozoa and oocytes by diploid organisms through meiosis |
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Timing of gametogenesis |
Males - Starts at puberty and continues thoughout life
Females - Starts during embryonic life and ends for each particular oocyte after fertilisation |
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4 stages of gametogenesis |
1) Formation and migration of primordial germ cells 2) Mitotic increase of germ cell numbers 3) Meiotic reduction 4) Differentation and maturation |
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Origin of games |
PGC (Primordial Germ Cells) Shortly after implantation At about 4 weeks of pregnancy PGSs arise in the yolk sac Alkaline phosphatase |
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Formation of spermatogonia and oogonia |
**picture** |
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Oogenesis |
Is the process of: -Formation -Development -Maturation ...healthy female gametes |
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Oogenesis(Prenatal period) Cluster of oogonia Follicular cells |
1) Period of proliferation PGC -> Oogonia (production of diploid cells by mitosis) Cluster of oogonia (3rd month) - Oogonia are surrounded by follicular cells Follicular cells - Layer of cells surrounding ovarian follicle (Nutrient providing for growth and maturation of the developing oocyte) |
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Oogenesis(Prenatal period) Period of growth Oocyte? Primary oocyte enters prophase 1? Stages? |
Oogonia -> Primary oocyte 5th month -> Degeneration begins (7 million) 7th month -> Meiosis 1 Oocyte - single cell surrounded by follicular cells Primary oocyte enters prophase 1 (period of intense metabolic activity, oocyte accumulates proteins) Stages: Leptotene, zygotene, pachytene, diplotene and then stop for interkinesis |
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Lampbrush chromosomes (Dictioneme chromosomes) |
The chromosomes have a lamp brush structure, with a dense inactive backbone and genetically active loops |
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Postnatal period (Time of birth) |
Diplotene stage, 700000 - 2 millions primary oocytes in ovaries (Remains to here to puberty) |
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Postnatal period (Maturation period) |
At puberty 400000 primary oocytes 5-15 start maturation only 1 mature primordial follicle becomes primary follicle |
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Process of maturation (Maturation period |
! |
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Primary follicle |
Granulosa cells become enlarged and cuboidal |
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Primordial follicle |
Single layer of squamos granolas cells |
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1) |
Primordial follicle becomes Primary follicle
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2) |
Primary follicle enlarges Granolas cells form more than 1 layer Zona pellucida forms |
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3) |
Primary follicle becomes secondary follicle Fluid filled vesicles develop among the granolas cells and theca is visible around the granolas cells |
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Theca interna |
Secrete hormones and is rich in blood vessels |
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Techa externa |
Like connective tissue |
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4) Mature follicle |
Fluid filled vesicles form a single antrum |
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5) Ovulation |
Oocyte is released from the follicle along with some surrounding granolas cells called corona radiata |
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6) Corpus luteum |
Following ovulation, granolas cells divide quickly forming the corpus lute which then degenerates forming the corpus albicans |
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Spermatogenesis |
Process of -Formation -Development -Maturation ....of healthy male gametes |
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Seretoli cells |
Located in seminiferous tubules Tall columnar epithelial cells -large nucleus -abundant in euchchromatin -well developed golgi complex -many mitochondria -extended smooth ER |
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Seretoli cells/Function |
Surround developing sperm cells Secrete proteins and fluids Feed sperm cells Synchronise the events of spermatogenesis |
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Seminiferous tubules |
**Picture** |
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Spermatogenesis 1 Period of proliferation |
PGC´s ->spermatogonia (2n) by Mitosis **Picture** |
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Period of proliferation/Spermatogonia/2 types A spermatogonia B spermatogonia |
A-Spermatogonia Continues supply of spermatogonia to fuel spermatogenesis B-Spermatogonia Gives rise to primary spermatocytes |
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2. Period of growth |
spermatogonium(2n) ->primary spermatocytes (2n) |
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3) Maturation period |
**Picture** |
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Cytoplasmic bridges/Spermatogonial synctia |
Cytokinesis not done and cells sticks together by cytoplasmic bridges because cells are dependant on proteins from the diploid genome. Ex. Akap 82 (Located on the x-chromosome), needed for formation of the sperm tail. New sperm cells have half x chromosome and half y chromosome, and if they were to be separated only the x chromosome sperm would mature and undergo spermiogenesis |
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Spermiogenesis |
1) Formation of a acrosome 2) Nuclear morphogenesis 3) Formation of a sperm tail 4) Rearrangement of organelles **Picture** |
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Gene regulation |
Primary spermatocytes (2n,XY) undergoes x-inactivation cause these are the only diploid cells without a active x chromosome. Developing male cells have some reserve mRNA which is used after the inactivation |
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Abnormal gametes |
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Kartagners syndrome |
Sperm cell lacks dynein arms making sperm cell inmobile Symptoms: Progressive damage to lungs Dislocation of organs Sterile **Picture** |
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Disjunction |
In meiosis the pair of chromosomes are supposed to split up and go to different spots in the dividing cell |
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Nondisjunction |
1 pair doesn't divide and a whole pair goes to one spot and this means that the resulting cells will have 24 chromosomes and the other will have 22 chromosomes |
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Downs syndrome |
If a sperm or a egg with abnormal number of chromosomes merges with a normal mate the resulting egg will have an abnormal number of chromosomes. In Down´s syndrome, 95% of all cases are caused by this event. **Picture** |
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Comparison of oogenesis and spermatogenesis Oogenesis |
Oogenesis Involves mitosis and meiosis Process produces 4 haploid daughter cells Process begins before birth Process ends at menopause One primary oocyte -> 1 egg and polar bodies One oocyte matures each month Nuclear division takes place at end of oogenesis There are 3 stages |
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Comparison of oogenesis and spermatogenesisSpermatogenesis |
Involves mitosis and meiosis Process produces 4 haploid daughter cellsProcess begins at puberty Process ends at death One primary spermatocyte forms 4 sperm cells Billions are produced at the same time Cytokinesis is not completed until the end of spermatogenesis There are 4 stages |
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Genetic aspect of fertilisation |
1) Sperm makes contact to secondary oocyte and sperm binds to receptor on surface of the oocyte 2) Binding induces acrosomal reaction. The acrosome breaks and releases hydrolyses 3) Sperm and egg membranes interact 4) Membrane fuses 5) This causes cortical reaction which secures monospermy |
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Significance of fertilisation |
Diploid chromosome number is reestablished Mixing of paternal and maternal chromosomes takes place Changes in the eggs cytoplasm are induced |
