gametogenesis

Question 1

what are primordial germ cells

Answer 1

undifferentiated cells which have yet to become gametes or migrate to the gonads

Question 2

what are the mechanisms by which PGCs become germ cells

Answer 2

either by the presence of germ plasm or being induced by pluripotent stem cells

Question 3

what is the genital ridge

Answer 3

the embryonic gonads. they are formed in the coelom from cells in the dorsal body wall and the mesonephros (the embryonic kidney)

Question 4

what is the default development pathway

Answer 4

female. it only becomes male if the sex determining region Y SRY activates Sox9 gene to activate anti mullerian hormone

Question 5

how to male PGCs differentiate

Answer 5

they multiply at the genital ridge but only enter the meiotic cycle at puberty after they differentiate to spermatogonia

Question 6

how do female PGCs differentiate

Answer 6

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

Question 7

what is the role of retinoic acid RA

Answer 7

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

Question 8

describe spermatogenesis

Answer 8

A1 spermatogonia replicate in waves, they type B enter meiosis and produce spermatocytes. this happens in the seminiferous tubules of the testes

Question 9

describe spermiogenesis

Answer 9

spermatocytes produce spermatids (sperm) which are released in the vas deferens

Question 10

how do oocytes develop

Answer 10

alongside follicle cells. together they produce a glycoprotein membrane the zona pellucida

Question 11

when do oocytes complete meiotic cycles

Answer 11

they are arrested in P1 at birth. they complete meiotic cycles at ovulation and then fertilisation. divisions are uneven and polar bodies are produced

Question 12

what are the physiological features of oocytes (2)

Answer 12

they have a vitelline membrane over the plasma membrane and a cortical granule which is analogous to the acrosome in sperm

Question 13

how do species ensure species recognition

Answer 13

this is more important in broadcast spawning where fertilisation is external. recognition is ensured by chemoattractants and the acrosome reaction

Question 14

how is polyspermy prevented

Answer 14

by the fast block (sea urchins) and slow block (all animals) mechanisms

Question 15

what is the role of phospholipase C

Answer 15

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

Question 16

what is capaciation

Answer 16

uterine fluids weaken the acrosomal membrane which enables fertilisation. this is via the ZR3 receptor in mammals

Question 17

what is the cumulus oophorus

Answer 17

follicle cells which are secreted with the oocyte at ovulation to form a sticky layer. this ensures only healthy sperm can access the egg

Question 18

where is methyl found in DNA

Answer 18

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

Question 19

what is genomic imprinting

Answer 19

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