MEIOSIS Flashcards
What is meiosis?
Type of cell division that happens in reproductive organs to produce sex cells/gametes
- Cells that divide this way are diploid to start with
- But sex cells that’re formed are haploids
- Cells formed by this type genetically different from parent cell & each other
Should u be able to a similarity with mitosis?
HECK YEA
What consists of meiosis?
Meiosis has two divisions:
Meiosis I = The homologous pairs split up
Meiosis II = Chromatids split apart, producing 4 haploid genetically different gametes
Can u even have enough time to learn what’s next?
IDK???? I need to start something but pls, where’s my backup plan?
Explain prophase I?
- Chromosomes condense and become visible
- Chromosomes come together as homologous pairs (synapsis)
Each homologous pair = bivalent - Non-sister chromatids wrap round each other and attach at points called chiasmata (singular: chiasma)
- They swap sections of chromatids with one another (crossing over)
- Nucleolus disappears & nuclear envelope disintegrates
-
Centriole move to opposite poles of the cell and a spindle forms
- Almost like mitosis prophase, however it seems chiasmata swap places
Visuals:
For the chromosome mixing part:
- There’s a paternal & maternal chromosome together (homologous pair)
- Course they get together by synapsis
- And btw together they’re called a bivalent
- Then, it’s like their legs are interlocking
two legs on top each other = chiasmata
a leg = chiasma
- Finally, it appears they swapped half of their legs, if u know u know
But in terms of the whole thing:
- Within we have chromosomes:
above can be paternal homologue, with chiasma happening
below can be maternal homologue
- Protected by nuclear membrane that’s currently disintegrating
- And we have the 2 centrioles on each side; above and below/sideways
N.B. Crossing over can happen in several places along the length of the chromatids, increases genetic variation. Long term, if species is to survive in a changing environment, sources of variation are essential.
Explain metaphase I?
- Bivalents lines up at equator of cell randomly, attached to spindle fibres at their centromeres
-
Allows chromosomes to independently segregate when pulled apart in anaphase I and a combination of paternal and maternal chromosomes goes into each daughter cell at meiosis I = independent assortment
Visuals:
- Practically looks exactly like metaphase in mitosis:
- Think of it as the basketball lines
- No nuclear membrane btw
- Centromeres above and below/sideways
- 4 “spindle fibres” (the lines between centromeres) with each chromosome connected (there is still chiasmata),
- From their centromeres
Showing Independent assortment:
- Basically u know how each cell has 2 homologous pairs (paternal and maternal)
- After meiosis, they can mix up in the 4 daughter cells
e.g. 1 with purely paternal and other with maternal
OR
1 with paternal and maternal and the same with the other
(Btw like, there’s like 2 different sizes the chromosome, like there’s a big maternal and small maternal, same with paternal. If u know u know)
Explain anaphase I?
(u fool)
- Homologous chromosomes in each bivalent are separated as spindle shortens & chromosomes pulled to opposite poles
- Centromeres do not divide (chromatids are still together)
Visuals:
- Still exactly like anaphase in mitosis:
- Just like the metaphase
- However the chromosome truly isn’t split
- And are going their separate ways (up/down/sideways, if u know u know)
Explain telophase I?
(but then…?)
- Nuclear envelope reforms around each set of haploid chromosomes
- There’s a brief interphase and chromosomes uncoil
- Cell now divides by cytokinesis
Visuals:
Bro just, it just looks EXACTLY like telophase….
TRANSITION
Cells now divide ‘mitosis style’
Explain prophase II?
- Nuclear envelope breaks down and nucleolus disappears
- Chromosomes condense
-
Spindles form
Visuals:
- Fr same as prophase in mitosis, but
- Centrioles replicate and move to poles
- New spindle fibres form at right angles to previous spindle axis
Explain metaphase II?
1 Chromosomes line up along the equator and spindle attaches to the centromere
2. Independent assortment happens because the chromatids of the chromosomes can face either pole - increasing genetic variation
Visuals:
- Fr same as metaphase in mitosis
Explain anaphase II?
- Centromeres divide and chromatids are pulled to opposite poles
Visuals:
- Okay now this time, they truly split apart
- Tho it’s actually 4 chromatids yano
Explain telophase II?
- Nuclear envelopes and nucleoli reform and the spindle disintegrates
- Chromosomes lengthen and are no longer visible
- Cytokinesis occurs
-
Four haploids, genetically different daughter cells are made
Visuals:
- So u know how the previous telophase there’s just 2
- This one has 4, each quarter type shit in a box
