Gametogenesis and fertilisation Flashcards
(49 cards)
What are PGCs?
Primordial germ cells that migrate from site of origin into gonad during early development.
What is the path PGCs take from development?
PGCs originate in extra-embryonic tissue, migrate into embryo via gut into genital ridge, PGCs multiply by mitosis as they migrate.
What does the genital ridge give rise to?
Somatic cells of the gonad (testis or ovary).
How do PGCs divide and what do they produce?
Divide by meiosis to produce gametes.
How does meiosis affect the chromosome number and what does it introduce?
Reduces chromosome number by half and introduces genetic variability.
When does meiosis occur in spermatogenesis?
Before differentiation.
What do PGCs do in embryo during spermatogenesis?
Multiply during migration to generate spermatogonia that arrest in G1.
What happens during spermatogenesis after birth and in adult?
Diploid spermatogonia multiply by mitosis to generate spermatocytes which enter meiosis.
What are syncytia and what yields them during spermatogenesis?
Haploid spermatids connected by cytoplasmic bridges, via incomplete cytokinesis.
What does formation of syncytia allow?
Synchronisation of maturation and sharing of gene products.
What is the final step of spermatogenesis?
Spermatids differentiate into spermatozoa, 4 gametes from each primary spermatocyte.
What are the first three steps of spermiogenesis?
Golgi develops into acrosomal cap, flagellum develops, cytoplasm extruded.
What are the last four steps of spermiogenesis?
Mitochondria coalesce near base of flagellum, arginine rich protamines replace histones, nucleus condenses, cytoplasmic bridges lost.
What is the sperm head specialised to do?
Aid penetration of outer coverings of egg.
What are the components of a spermatozoon?
Head = acrosome and nucleus, midpiece = centriole and mitochondria, tail = plasma membrane and flagellum.
What does the acrosome contain lytic enzymes for on sperm?
Protein digestion, carbs digestion, lipid digestion.
What is the sperm flagellum specialised for?
Motility.
What does the axoneme in sperm tails contain?
Contains 2 central singlet microtubules surrounded by 9 doublet microtubules, dynein attached to MTs.
What role does dynein have is bending flagellum/tail?
Uses energy of ATP hydrolysis to slide the MTs past one another, which causes bending.
When does meiosis occur in oogenesis?
After differentiation.
What are the steps of oogenesis in embryo?
PGCs multiply by mitosis during migration to generate oogonia that continue to divide by mitosis, diploid oogonia enter meiosis and arrest in prophase of meiosis 1 as primary oocytes.
What are the steps of oogenesis in adult?
Primary oocytes grow and mature, upon ovulation meiosis 1 is complete, secondary oocytes arrest in metaphase II, meiosis II completed after fertilisation (1 ovum and 2 polar bodies from each primary oocyte).
What are eggs specialised to generate?
New individual with nutrient reserves and an elaborate coat.
How are eggs specialised?
Nutritive yolk proteins, protein synthesis machinery, mRNAs encoding proteins needed for early development, morphogenetic factors to direct early development, protective chemicals e.g. UV filters, extracellular glycoprotein coat.
