gametogenesis Flashcards
what are primordial germ cells
undifferentiated cells which have yet to become gametes or migrate to the gonads
what are the mechanisms by which PGCs become germ cells
either by the presence of germ plasm or being induced by pluripotent stem cells
what is the genital ridge
the embryonic gonads. they are formed in the coelom from cells in the dorsal body wall and the mesonephros (the embryonic kidney)
what is the default development pathway
female. it only becomes male if the sex determining region Y SRY activates Sox9 gene to activate anti mullerian hormone
how to male PGCs differentiate
they multiply at the genital ridge but only enter the meiotic cycle at puberty after they differentiate to spermatogonia
how do female PGCs differentiate
they differentiate to oogonia at the genital ridge and immediately enter the meiotic cycle, differentiating into oocytes. they have a set number of gametes at birth
what is the role of retinoic acid RA
it controls differentiation of PGCs. in females it induces the TF Str8 for DNA synthesis and entry to the meiotic cycle. in males they have an enzyme Crp26 which degraded RA to prevent entry to the meiotic cycle
describe spermatogenesis
A1 spermatogonia replicate in waves, they type B enter meiosis and produce spermatocytes. this happens in the seminiferous tubules of the testes
describe spermiogenesis
spermatocytes produce spermatids (sperm) which are released in the vas deferens
how do oocytes develop
alongside follicle cells. together they produce a glycoprotein membrane the zona pellucida
when do oocytes complete meiotic cycles
they are arrested in P1 at birth. they complete meiotic cycles at ovulation and then fertilisation. divisions are uneven and polar bodies are produced
what are the physiological features of oocytes (2)
they have a vitelline membrane over the plasma membrane and a cortical granule which is analogous to the acrosome in sperm
how do species ensure species recognition
this is more important in broadcast spawning where fertilisation is external. recognition is ensured by chemoattractants and the acrosome reaction
how is polyspermy prevented
by the fast block (sea urchins) and slow block (all animals) mechanisms
what is the role of phospholipase C
it mediates the slow block mechanism. it causes release of Ca2+ which hardens the envelope and DAG activates a proton pump, increasing the pH which causes synthesis of DNA/ RNA/ proteins
what is capaciation
uterine fluids weaken the acrosomal membrane which enables fertilisation. this is via the ZR3 receptor in mammals
what is the cumulus oophorus
follicle cells which are secreted with the oocyte at ovulation to form a sticky layer. this ensures only healthy sperm can access the egg
where is methyl found in DNA
it is highly concentrated in DNA, found mainly as 5- methylcytosine. in sperm the DNA is demethylated before the pronuclei fuse via the Tet enzyme
what is genomic imprinting
some genes can also be expressed if they are maternally or paternally inherited. for this reason the male and female pronuclei are both required for the embryo to develop- not because of the Y chromosome
