Devo Lect 4 - Gametogenesis Flashcards Preview

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Flashcards in Devo Lect 4 - Gametogenesis Deck (18):
2

Compare egg and sperm

Size, motility; both haploid, both went through meiosis

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Gametogenesis (in development)

Germline tissue develop separately from somatic tissue early - primordial germ cells -

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Spermatogenesis

Seminiferous tubules contain mature sperm in lumen; progress in stages (layers of cells)

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Leydig cells and sertoli cells

Leydig b/w seminiferous tubules produces testosterone; sertoli in seminiferous tubules secrete GDNF, regulates fate of developing sperm

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Process of spermatogenesis, and time required

Spermatogonium (diploid) stem cell; primary spermatocytes; secondary spermatocytes; spermatids (haploid); mature sperm; takes 74 days in humans (35 in mice)

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Spermiogenesis

Differentiation of the haploid spermatid to mature sperm (ie this is part of the process of spermatogenesis)

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Structure of sperm

Small, little cytoplasm (lighter); nucleus condensed; mitochondria in midpiece; flagella (axoneme); acrosomal vesicle; generally conserved in animals, some plants

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Acrosomal vesicle

Modified lysosome in head of sperm;

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Axoneme

Core of flagella; 9 + 2 microtubule arrangement, tubulin; dynein motor causes flagella bending to create movement

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Gene expression in spermatogenesis

ß-tubulin: meiotic spindles, axoneme; dynein: motor unit; histone genes: chromatin condensation; genes for recognition proteins

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Kartagener syndrome

mutation in dynein gene; one or both arms absent; results in infertility, problems with cilia too (chest infections, egg doesn’t move in fallopians)

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Oogenesis differences in species

many eggs or few, depends on species (parental care)

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Oogenesis in mammal

Oogonium (diploid stem cell); primary oocytes (still diploid); 1 ovum + 3 polar bodies (uneven meiosis required to have correct number of chromosome); controlled by FSH; meiosis often not complete in mature follicle!

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FSH

affects the follicle to develop into Graafian follicle (contains egg undergoing meiosis); then ovulation occurs; some granulosa cells from follicle become cumulus

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When does meiosis complete in human egg?

After sperm meets egg

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Egg structure

large; stores of enzymes, mRNA (for early development), yolk proteins etc;

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Comparing different eggs

Sea urchin: egg secretes jelly layer outside (glycoproteins), vitelline envelope; mammal: zona pellucida (thick ECM), cumulus layer of cells

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Parthenogenesis

Some species can reproduce without a gamete from another; aphids, insects, sometimes occurs under unusual circumstances (aquariums); either includes one of the polar bodies (diploid), or viable haploid offspring. NOT mammals; Pro: colonize; Con: low genetic diversity