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Cell Bio And Disease > Meiotic Cycle > Flashcards

Meiotic Cycle Flashcards

1
Q

What is meiosis for

A

Sexual reproduction

Production of haploid gametes for fertilisation to form a diploid zygote

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2
Q

How many interphases/s phases is there

A

1, doesn’t occur in meiosis 2

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3
Q

When does genetic variation for meiosis occur

A

Crossing over of homologous chr in prophase

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4
Q

When does female meiosis stop in oocytes

A

As a foetus still, oocyte stops in prophase 1 till puberty/ovulation every 4 weeks where it arrests up to metaphase 2

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5
Q

What complex holds homologs together

A

Synaptonemal complex

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6
Q

What are the 4 prophase stages

A

Leptonene - pairing
Zygotene - synaptonemal complex form
Pachytene - crossing over as complex complete
Diplotene - removal of complex so chiasma is visible for metaphqse

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7
Q

Where does hr occur

A

On 2 arms 1 from each homolog (left with 2 non recombinant arms)

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8
Q

Where does meiosis occur in females and males

A

Gonads (testes or ovary)

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9
Q

What are the progenitor cells which undergo meiosis

A

Primary Spermatocytes or primary oocytes (4n)

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10
Q

What is puberty triggers division in meiosis 1 to form a secondary oocyte and a polar body

A

LH

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11
Q

What is the diff between cohesin removal in mitosis and meiosis

A

Mitosis is prophase by aurora b,wapl or plk. Then separase in metaphase

Meiosis has 2 steps both including separase

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12
Q

When do cohesin rings in meiosis get removed

A

Meiosis metaphase II to separate sister chromatids

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13
Q

What is cleaved by separase in meiosis of the cohesin complex

A

Rec 8 (mitosis equivalent of scc1)

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14
Q

What protein protects centromere cohesin in meiosis 1

A

Shugosin

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15
Q

What does shugoshin do

A

It recruits ppa2 which dephos rec8 so it’s not recognised by separase anymore

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16
Q

What in meiosis 2 allows centromere cohesin removal

A

I2 ppa2 inhibitor

Stops dephos of rec8 and rec8 can be degraded once phosphorylated

17
Q

Why are older females not protected as much from cohesin removal forming impaired bi orientation

A

Low sgo2 and rec8

18
Q

Meiosis 1 the kinetochores are mono orientated. What does this mean

A

Both kinetochores on sisters attach to one spindle

Pulls homologs apart

19
Q

Why is mitosis not got sgo2

A

Not mediated by separase in first phase

20
Q

What is aneuploidy

A

Extra or missing chromosomes due to non disjunction in meiosis

21
Q

Which cells are bigger, oocytes or somatic cells in mitosis

A

Oocytes

22
Q

Why is bipolar spindle assembly harder in oocytes

A

No centrosomes

They have to use mt organising centres which takes a long time to form bipolarity

23
Q

What is the time difference between meiosis and mitosis

A

24-36hrs vs 10 minutes

24
Q

Cdk is in excess in mitosis, is this the same in meiosis

A

No, excess cyclin b

25
Q

Why does correction of spindle attachments take longer in meiosis

A

90% error rate compared to 10-30% in mitosis

26
Q

How many rounds of error correction in meiosis taking 50mins each

A

6

27
Q

Where does spindle have to migrate and why in meiosis (takes long)

A

Cortex of egg because it divides asymmetrically to polar body and oocyte

28
Q

What is the issue with bivalent homologs which takes a long time in meiosis

A

67% collapse so need reattached

29
Q

What does meiosis 1 and 2 division get driven by in puberty then finally after fertilisation

A

Cdk1 and cyclin B (2 waves)

30
Q

What needs to happen to cyclin B to exit meiotic division

A

Degradation via apc

31
Q

Is there any difference in sac in meiosis

A

NO, also mcc which blocks cyclin B deg and separase

32
Q

They found cyclin B is degraded even in sac presence, why didn’t this affect cdk1 activity (cdk1 was still active)

A

Bc meiosis there is excess cyclin B which does not bind to cdk1

Cyclin B which is free binds apc cdc20 in a different place which mcc can’t block

33
Q

What is the result of cdk1 action not lowering

A

Longer prometaphase and can’t enter anaphase, allows correct attachment more likely

34
Q

Which phase is secondary oocyte held in before fertilisation

A

Metaphase II

35
Q

What holds sec oocyte in metaphase II and how

A

Cytostatic factor , it clamps and blocks apc cdc20 instead of sac preventing anaphase

36
Q

What mediates cytostatic factor csf activity in metaphase 2

A

Emi2

37
Q

How does sperm fertilisation stop the emi2/csf clamping in metaphase II

A

Sperm has PLC zeta whcih produces ip3 and dag

Ip3 causes ca increase

Ca causes calmodulin dep kinase II action

Cam K II phosphorylates emi2

Emi2 recognised by polo

Polo phosphorylates Emi2 further and degrades it

Apc cdc20 becomes active

Cell Bio And Disease (18 decks)

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