Meiotic Cycle Flashcards
What is meiosis for
Sexual reproduction
Production of haploid gametes for fertilisation to form a diploid zygote
How many interphases/s phases is there
1, doesn’t occur in meiosis 2
When does genetic variation for meiosis occur
Crossing over of homologous chr in prophase
When does female meiosis stop in oocytes
As a foetus still, oocyte stops in prophase 1 till puberty/ovulation every 4 weeks where it arrests up to metaphase 2
What complex holds homologs together
Synaptonemal complex
What are the 4 prophase stages
Leptonene - pairing
Zygotene - synaptonemal complex form
Pachytene - crossing over as complex complete
Diplotene - removal of complex so chiasma is visible for metaphqse
Where does hr occur
On 2 arms 1 from each homolog (left with 2 non recombinant arms)
Where does meiosis occur in females and males
Gonads (testes or ovary)
What are the progenitor cells which undergo meiosis
Primary Spermatocytes or primary oocytes (4n)
What is puberty triggers division in meiosis 1 to form a secondary oocyte and a polar body
LH
What is the diff between cohesin removal in mitosis and meiosis
Mitosis is prophase by aurora b,wapl or plk. Then separase in metaphase
Meiosis has 2 steps both including separase
When do cohesin rings in meiosis get removed
Meiosis metaphase II to separate sister chromatids
What is cleaved by separase in meiosis of the cohesin complex
Rec 8 (mitosis equivalent of scc1)
What protein protects centromere cohesin in meiosis 1
Shugosin
What does shugoshin do
It recruits ppa2 which dephos rec8 so it’s not recognised by separase anymore
What in meiosis 2 allows centromere cohesin removal
I2 ppa2 inhibitor
Stops dephos of rec8 and rec8 can be degraded once phosphorylated
Why are older females not protected as much from cohesin removal forming impaired bi orientation
Low sgo2 and rec8
Meiosis 1 the kinetochores are mono orientated. What does this mean
Both kinetochores on sisters attach to one spindle
Pulls homologs apart
Why is mitosis not got sgo2
Not mediated by separase in first phase
What is aneuploidy
Extra or missing chromosomes due to non disjunction in meiosis
Which cells are bigger, oocytes or somatic cells in mitosis
Oocytes
Why is bipolar spindle assembly harder in oocytes
No centrosomes
They have to use mt organising centres which takes a long time to form bipolarity
What is the time difference between meiosis and mitosis
24-36hrs vs 10 minutes
Cdk is in excess in mitosis, is this the same in meiosis
No, excess cyclin b
