Meiosis

Question 1

What is meiosis

Answer 1

• A type of cell division that reduces the no of chromosomes in the parent cell by half and produces 4 gamete cells

Question 2

Explain meiosis

Answer 2

• Takes place in the sex organs
  
  • ovaries and testies in animals
  • anthers and ovules in plants
• AKA reduction division, thus an ovum or sperm cell has half the no of chromosomes that is a characteristic of a species ( haploid)
  - when they join they become diploid
• When a zygote is formed, homologous chromosomes ( identical ) pair up
• Female zygote = 44 autosomes and 2 X chromosomes
• Male zygote = 44 autosomes and XY
• Sex chromosomes = also gonosomes

Question 3

What happens in the first division

Answer 3

• Homologous pairs separate
• Chromosome no = halved
• 2 daughter cells formed

Question 4

What happens in the second division

Answer 4

• Similar to mitosis
• 4 daughter cells formed
• Each with a different genetic make-up

Question 5

What occurs before meiosis

Answer 5

DNA Replication ( in interphase)

Question 6

What happens in interphase

Answer 6

• DNA rep occurs
• Single stranded chromosomes becomes double threaded
• Each chromosome has 2 chromatids attached together with a centromere

Question 7

Explain Prophase 1fully

Answer 7

-Chromatin network shortens
- Homologous chromosomes pair up ( one maternal and one parental) = homologue
- 4 chromatid structure = bivalent
- An exchange of genetic material occurs between chromatids of a homologous pair ( AKA crossing over & the point of crossing over = chiasma)
-Nuclear membrane and nucleolus disintegrate
- centrioles in animals cells move to opposite poles

Question 8

Explain Metaphase 1 fully

Answer 8

• Homologous pairs line up at the equator randomly in double file
• Random arrangement of chromosomes introduces genetic variation
• Spindle fibres become attached to the centromeres

Question 9

Explain Anaphase 1 fully

Answer 9

• Spindle fibres shirten and the chromosomes in each bivalent separate and move to opp. poles

Question 10

Explain what happens in Telophase 1 fully

Answer 10

• Double threaded chromosomes arrive at poles where they gather together
• A nuclear membrane forms around each set of chromosomes to create 2 nuclei ( karyokinesis)
• Cytokinesis takes places as final stage of cell division
  -2 daughter cells each containing half the no of chromosomes as parents but are still double threaded
• Cell plate forma along equator in plant cells and a new plasma membrane and cell wall form along each side of the cp§

Question 11

Explain what happens in Prophase 2 fully

Answer 11

-Nucleus disintegrates
- Nuclear membrane disintegrates releasing the chromosomes
- SF form again

Question 12

Explain what happens in Metaphase 2 fully

Answer 12

• Double threaded chromosomes line up along the equator in single file
• Spindle fibres attach to the centromere of each of the sister chromarids

Question 13

Explain what happens in Anaphase 2 fully

Answer 13

-Centromeres split and each daughter chromosome is pulled to opposite sides
- Cleavage furrow appears at the equator marking the beginning of cytokinesis

Question 14

Explain what happens in Telophase 2 fully

Answer 14

• Single threaded chromosomes arrive at the poles
• A nuclear membrane forms around each set of chromosomes to create 2 new cell nuclei ( a new nucleolus reforms in each cells)
• Cytokinesis occurs once more
• 4 genetically different daughter cells each with half the no of chromosomes