Meiosis

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Meiosis

Did you even think...

- why organisms with sexual reproduction have the correct number of chromosomes?

- why genetic variation is possible although mitosis ends up with 2 identical daughter cells? 

Learning objectives

• You can list and describe the phases of meiosis
• You can describe changes in number of chromosomes during meiosis
• You can explain changes in DNA content during meiosis
• You can explain the importance of meiosis (in terms of genetic variation)

Cell cycle and cell division

Interphase: G1, S, G2

Cell division: Mitosis or Meiosis

Meiosis

• PMAT (twice)
• Meiosis I:  
  - Splitting homologous pairs
  - 2n --> n+n
• Meiosis II:
  - Splitting chromatids
  - n --> n+n: end result is 4 haploid cells

Prophase I

• Nuclear membrane brakes down
• Spindle appears
• Homologous pairs are together
• Crossing over occurs

Metaphase I

• Chromosomes line up on the equator in pairs
• Homologous pairs still together
• Spindle fibers connect to one member of the pair 

Anaphase I

• Spindle fibers pull the homologous pairs apart
• Sister chromatids stay attached! 

Telophase I

• Nuclear membranes form 

Cytokinesis

• Cytoplasm splits
• Each cell is now haploid 

Prophase II

• Nuclear membrane brakes down
• Spindle fiber forms
• No crossing over! 

Metaphase II

• Chromosomes line up at the equator
• Each chromosome connects to two spindle fibers 

Anaphase II

• Chromatids are pulled apart! 

Telophase II

• Nuclear membranes form 

Cytokinesis

• Cytoplasm splits
• 4 unique haploid cells are formed

Which best describes the number of chromosomes for Meiosis I?

1. 2n -> 2n+2n
2. 2n -> n + n
3. n -> n+n
4. n -> 2n +2n

Which best describes the number of chromosomes for Meiosis II?

1. 2n -> 2n+2n
2. 2n -> n + n
3. n -> n+n
4. n -> 2n +2n

Final result of meiosis is:

1. 2 genetically identical daughter cells
2. 4 genetically identical daughter cells
3. 2 genetically different daughter cells
4. 4 genetically different daughter cells

Crossing over takes place during:

1. Prophase I
2. Prophase II
3. Anaphase II
4. Metaphase II

Does crossing over occur between homologous pairs?

1. true
2. false

Exercise: Recognizing the phases of Meiosis

Google Classroom

Fill in the worksheet: Meiosis. Recognizing the phases.

Consult presentation, your neighbour for help

10' to work on

Upload the document to the Google Classroom

Homework

• Watch the video on the next slide
• Read pages from the book 105-109