94. primordial germ cells/ gametogenesis

Question 1

What are gametes derived from

Answer 1

primordial germ cells (PGCs) originate in the primitive streak?

formed in the epiblast in the 2nd week

moves to the wall of the yolk sac

Question 2

Where do the PGCs migrate to after the 4th week

Answer 2

the gonads (organ that produces gametes)

Question 3

how do PGCs increase in number during migration through embryo/ when they arrive at gonads

Answer 3

mitosis

Question 4

what can germ cells undergo in preparation for fertilization

Answer 4

gametogenesis- making male and fem gametes which includes meiosis

cytodifferentiation- completes their maturation

Question 5

What are the forms of gametogenesis

Answer 5

oogenesis
spermatogenesis

Question 6

what are germ cell tumours called

Answer 6

teratomas (monster tumours)

they are composed of all 3 germ layers

can occur in the gonads or extragonadally

Question 7

what is the cell division that occurs in germ layers to make gametes

Answer 7

meiosis -

meiosis 1’(homologous chromosomes line up in equator) + meiosis 2 (chromosomes line up)

Question 8

what happens during meiosis 1 that increases genetic variability

Answer 8

crossing over

when segments of chromatids are exchanged at the chiasmata

Question 9

how many daughter cells arise from primary oocyte/ primary spermatocyte

Answer 9

4 for each

oocyte: each has 22+x chromosomes but only 1 becomes mature gamete other 3 become polar bodies

sperm: 2 has 22+x chromosome, 2 has 22+Y chromosomes. no polar bodies