Session 3 - gametes REPRO Flashcards
(42 cards)
where do germ cells originate from
in yolk sac wall near allantois
where do they migrate
gonadal ridge
how do they move
ameoboid manner , tilting and moving
what determines gender and as a result what develops and from where
if germ cell has 2 X chromosomes then will colonise the cortex of gonad (ovary formed) if it has Y chromosome medulla of gonad is colonized (testes)
default an ovary, prescience of Y chromosome precedes male development
what is SRY
gene on Y chromosome (sex determining region on y chromosome) codes for transcription factor and activates differentiation events and develop testes
testes determining factor
what happens once germ cells arrive at gonad
proliferate by mitosis (germ cells from spermatogonia –> will give rise to sperm (gametes))
genetic reshuffling and reduce to haploid by meiosis (in gonads–> Fallopian tube?)
cytodifferentiate into mature gametes
why is genetic reshuffling important
to ensure genetic diversity in offspring
what germ cell determines the sex of the embryo
sperm since it has either x or Y chromosome
what are the 2 main functions of meiosis
introduce genetic diversity
reduce chromosome number in gamete to 23
what is a bivalent and the role of meiosis one
one chromosome from mum and one from dad duplicate to form bivalent
role of meiosis one is to split bivalent into 2 daughter cells
what is the role of meiosis 2
split bivalent into 4 daughter cells
how many daughter cells are produced from male and female germ cells
define what polar bodies are
4 daughter cells, 1 daughter cells other 3 lost in structures called polar bodies (waste basket for genetic material)
how does genetic variation occur
crossing over (swap regions of DNA between 2 non sister) —> create diversity
independent assortment (each bivalent can align on metaphase plate independently)
random segregation (random distribution of alleles among the 4 gametes)
where does spermatogenesis occur
semineforus tubules
what do retes testis do
concentration leaving sperm
what do Sertoli cells do
nurture developing spermatids from spermatogonia (made between sertoli cells)
what are the 2 barriers of Sertoli cells and why are they important
basal and lumen compartments (due to tight junctions) form blood testis barrier (Sertoli cell barrier) important cuz of different cell environment (making vs developing spermatids in sertoli gaps)
due to diversity could have immune response against sperm cuz recognised as non self (Dif genetic complement) so it prevents this
what is spermatogonia
(male germ cells) are raw material for spermatogenesis
generate 4 mature spermatids
describe sperm production
germ cell divide by mitosis to make ad spermatogonium and ap spermatogonium which are primary spermocytes
primary divide by meiosis to make secondary spermatocytes and then spermatids
remember each primary spermatocyte forms 4 haploid spermatids which turn into spermatozoa (normal sperm)
what are ad and ap spermatogonium
ad is resting stock and only used when called upon
ap is active and maintains stocks from puberty onwards , produce type B spermatogonia which give rise to spermatocytes
what is the spermatogenic cycle
time taken for reappearance of same stage within given segment of tube
16 days
what is the spermatogenic wave
distance between same stage (same as cycle but this measures distance not time)
what is permeation
spermatids released into lumen of ST
describe what happens as they make their way into epididymis
remodel as they pass down ST, through rate testies into ductile efferent and into epid to finally form spermatozoa
however, non motile and only move due to peristaltic contraction and Sertoli cell secretion until they reach epid
