DB-Lec 3&4 - Biology 442 Biology Developmental...

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Biology 442 Biology 442 Developmental Biology Developmental Biology Lectures 3 & 4 – Gametogenesis Lectures 3 & 4 – Gametogenesis
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Gametogenesis Gametogenesis is the formation of is the formation of the the gametes gametes Two types of gametes – sperm sperm and egg egg . They are cells specialized for reproduction. Gametogenesis takes place in the gonads gonads : in females; the ovaries ovaries and in males; the testes testes . The gametes – sperm and egg are haploid (1N). Fertilization results in the fusion of the gametes to form the zygote zygote or fertilized egg which is diploid (2N)
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August Weismann (1834-1914) developed the concept of the germ line . The germ line is the lineage of cells from which the gametes arise. Cells that do not give rise to gametes are known as the somatic cells The cells that will produce the germ line are known as the primordial germ cells . They can be distinguished from somatic cells by size, shape, division schedule, motility and the expression of certain “marker proteins or mRNAs”
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1) formation of primordial germ cells 2) migration of primordial germ cells to gonad 3) mitotic division of primordial germ cells to give (germ cells) 4) meiosis of germ cells to give gametes 5a) making sperm 2 processes spermatogenesis and spermiogenesis 5b) making oocytes/eggs (oogenesis) Topics we will cover Topics we will cover
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Primordial germ cells are “ Primordial germ cells are “ determined determined ” early ” early in embryonic development. in embryonic development. In many animals – determination of cells to the germ line occurs by the localization of cytoplasmic determinants found in the egg cytoplasm. In the zygote this region of the cytoplasm is called germ plasm or pole plasm – cells that get this cytoplasm become Primordial Germ Cells
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This cytoplasm often has things in it you can see– polar granules in flies, P granules in C. elegans In Drosophila PGCs form at the posterior pole 4 types of components identified as being in polar granules Proteins including oskar (localizes proteins and mRNA to germ cells), nanos (prevents mitosis and transcription during germ cell development), vasa (RNA binding protein) mRNA for the germ cell-less gene (mutations result in females who cant have grandchildren) Mitochondrial rRNA Non-translatable RNA called polar granule component (antisense knock downs cant migrate)
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Staining for gcl mRNA in Staining for gcl mRNA in Drosophila egg and embryo Drosophila egg and embryo
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Segregation of the P granules to the germ line Segregation of the P granules to the germ line precursor cell (P4 blastomere) in Nematodes precursor cell (P4 blastomere) in Nematodes The components of the P granules include several transcriptional inhibitors and RNA binding proteins.
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