Meiosis

Question 1

What happens during interphase?

Answer 1

1. Cell grows, stores energy and duplicates organelles.
2. The DNA replicates and the DNA content of the cell doubles. The chromosome number still remains 2n.
3. The 2 identical chromatin threads are joined together at the centromere. They are called sister chromatids.
4. The chromatin threads are in the dispersed state.

Question 2

What happens during prophase I?

Answer 2

1. The chromatin condenses to form chromosomes, which are visible under the light microscope.
2. Homologous chromosomes pair up.
3. Crossing-over occurs when the chromatids of homologous chromosomes cross and twist around one another.
   - The point where they cross over is called a chiasma.
   - Crossing over results in new combinations of alleles along the chromosomes.
4. The nuclear envelope and nucleolus disappears.
5. Asters, which are structures made of microtubules, form around the centrioles.
6. The 2 centrioles move apart to opposite sides of the cell.
7. Spindle fibres extend from one pole of the cell to the other.

Question 3

What happens during metaphase I?

Answer 3

1. The homologous chromosomes line up along the metaphase plate, which is equidistant from the 2 poles.
2. The 2 chromosomes of each pair face opposite sides of the cell and each chromosome is attached to a spindle fibre.

Question 4

What happens during anaphase I?

Answer 4

1. Homologous chromosomes separate and move to opposite sides of the cell. The sister chromatids are still attached and move together.
2. The opposite ends of the cell move further apart.

Question 5

What happens during telophase I?

Answer 5

1. Spindle fibres break down.
2. Daughter nuclei begin to form at both ends of the cell - nuclear envelope and nucleolus reform.

Question 6

What happens during cytokinesis I?

Answer 6

1. The 2 daughter cells are pinched apart.
2. Each daughter cell has a haploid number of chromosomes.
3. Centrioles divide