Meiosis

Question 1

Meiosis
key points

Answer 1

• cell division of germ cells in sexually reproduccing organisms to produce gametes (e.g. sperm or egg cells)
• 2 rounds of division = 4 cells with each ONE copy oh each chromosomes (haploid)
• paternal and maternal genetic information on chromosomes are crossed, creating nwe code combination on the chromosomes
• during fertilisation, haploid cells produced by meiosis from male and female fuse = 2 copies of each chromosome again (zygote)

Question 2

Phases of meiosis

Answer 2

• meiosis I and meiosis II devided into Karyokinesis I and Cytokinesis I and Karyokinesis II and Cytokinesis II respectively
• same preparatory stahe as mitosis ( G1,S,G2)
• Meiosis I and II are each divided into:
  Prophase
  Metaphase
  Anaphase
  Telophase

Question 3

Meiosis I - Prophase 1

Answer 3

• longest phase
• Homologous maternal and paternal chromosomes pair, synapse, and exchange genetic information (by homologous recombination), forming at least one crossover per chromosome

Question 4

what happens in meiosis I - prophase 1?
pt (1)

Answer 4

• this stage in devided into series of sunstages names according to the apperance of chromososmes:
  1. Leptotene
  2. Zygotene
  3. Pachytene
  4. Diplotene
• DIAKINESIS
  - chromosomes condence further
  - nuclear memebrane disintagrates into vescicles
  - meiotic spindle begins to form
  - (resembles prometaphase in mitosis)

Question 5

What happenes in
Meiosis I – Metaphase 1?

Answer 5

• homologous pairs move along metaphase plate
• kinetochore microtubles from both sindle poles attach to respective kinitochores
• paired homologous chromosomes alingh=n along an equatorial plane that bisects the spindle

Question 6

what happens in Meiosis I – Anaphase 1?

Answer 6

• Kinetochore microtubules shorten = pull homologous chromososmes to opposite poles
• Non-kinetochore microtubules lengthen, pushing the centrosomes farther apart
• cell elongates in separation for division down the centre
• sister chromatids remain together
• homologous are segregated

Question 6

Meiosis I – Telophase 1 & Cytokinesis

Answer 6

• fiest meiotic division end when chromosoems arrive at the poles
• each daughter cell had half the number of chromosomes, each chromosome has a pair of hromarids
• cell memebrane is pintched = creation of 2 daughter cells
• here, cytpkinesis isn’t fully complete, resulting in “cytoplasmatic bridges” enebling the cytoplasm to be shared betwee daughter cell untilll end of meiosis II

Question 7

Meiosis II – Prophase 2

Answer 7

• usually involves equestional segragation or separation of sister chromatids
• disappearance of nucleoli and nuclear envelope
• shortening and thickening of chromtids
• ## centronomes move to polar regions and arrange spindle fibres for 2nd metic division

Question 8

Meiosis II – Metaphase 2

Answer 8

• Centromeres contain 2 kinetochores that attach to spindle fibres from the centrosomes at opposite poles
• new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I – perpendicular to the previous plate

Question 9

Meiosis II – Anaphase 2

Answer 9

• Remaining centromeric cohesin, is cleaved, allowing the sister chromatids to segregate
• sister chromatids are now called sister chromosomes as they move toward opposing poles

Question 10

Meiosis II – Telophase 2 & Cytokinesis

Answer 10

• De-condensation and lengthening of the chromosomes
• disassembly of the spindle
• Nuclear envelopes re-form and cleavage or cell plate formation eventually produces a total of 4 daughter cells, each with a haploid set of chromosomes