Meiosis

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Meiosis

Learning objectives

• List and describe the phases of meiosis
•  Describe changes in number of chromosomes during the steps of meiosis
• Describe changes in DNA content during the steps of meiosis

Which best describes the amount of chromosomes during the cell cycle with mitosis? Express the number in n.

True or false?

Each homologous pair contains similar genes but different variants. 

Explain your answer.

Meiosis

• Goal: create haploid cells that will become the gametes
• Interphase is still the same
• Challenge: how to make sure all cells end up with one of each type of chromosome to make sure their set of genes is complete.

Chromosome numbers

Unique per species

Meiosis

• PMAT twice
• Meiosis 1:  
  - Splitting homologous pairs
  - 2n --> n+n
• Meiosis 2:
  - Splitting chromatids
  - n --> n+n: end results is 4 haploid cells

Prophase 1

• Nuclear membrane disappears
• Homologous pairs stay together
• Crossing over creates variation
• Spindle appears

Metaphase 1

• Chromosome line up on the equator in pairs
• Homologous pairs still together
• Each centriole connects a spindle fibre to one member of the pair 

Anaphase 1

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

Telophase 1

• Nuclear membranes form 

Cytokinesis

• Cytoplasm splits
• Each cell is now haploid 

Prophase 2

• Nuclear membrane disappears
• Spindle forms
• No crossing over! 

Metaphase 2

• Chromosome line up at the equator
• Each chromosome connect to two spindle fibers 

Anaphase 2

• Chromatids are pulled apart 

Telophase 2

• Nuclear membranes form 

Cytokinesis

• Cytoplasm splits
• 4 unique haploid cells 

GENETIC VARIATION

What are the five sources of genetic variation?

An ejaculation of a healthy man consists of 2-5 million sperm cells. Independent assortment has led to a huge genetic variation. Will all possible gametes be present in this ejaculation?

MUTATIONS

Alterations in the genome of an organism:

They can be spontaneous (molecular decay)

Due to environmental influences (radiation, mutagens)

What are the five sources of genetic variation?

Learning objectives

• List and describe the phases of meiosis
•  Describe changes in number of chromosomes during the steps of meiosis
• Describe changes in DNA content during the steps of meiosis

Work to be done

• Finish Biozone worksheets 136, 139 and 141
  
• Finish assessment questions Glencoe pg. 289: q. 1 – 11
  

Please order the four stages of Mitosis!

Prophase

Metaphase

Anaphase

Telophase

Interphase

What phase of mitosis do these images show?

Prophase

Metaphase

Anaphase

Telophase

00:22

Look at how the chromosomes are arranged at this point. What stage of mitosis is this?

1. Metaphase
2. Prophase
3. Anaphase
4. Telophase

00:35

A hard cell plate formed in the middle of this cell after mitosis. What type of cell did we just watch divide?

1. Plant cell
2. Animal cell

00:45

The cell in the video just underwent anaphase, how do you know this?

1. The cell split into two, distinct cells
2. The chromosomes pulled "away" from each other
3. The chromosomes arranged themselves on the equator of the cell
4. The cell's DNA was just replicated

What phase of mitosis do these images show?

Prophase

Metaphase

Anaphase

Telophase

Which best describes the amount of chromosomes during meiosis 1?

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

Which best describes the amount of chromosomes during meiosis 2?

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

C is a process happening during.. in ..

1. Anaphase / Meiosis 1
2. Anaphase / Mitosis
3. Metaphase / Meiosis 1
4. Metaphase / Mitosis

At the end of meiosis you end up with:

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

In anaphase of meiosis 2 the number of chromosomes is haploid

1. true
2. false

Crossing over takes place during:

1. Meiosis 1 / Prophase
2. Meiosis 2 / Prophase
3. Meiosis 2 / Anaphase
4. Meiosis 2 / Metaphase

Crossing over can only occur between homologous pairs

1. true
2. false