Meiosis

Question 1

Interphase

Answer 1

DNA replicated to produce two chromatids in each chromosome. Organelles replicate. ATP builds up from respiration.

Question 2

Prophase 1

Answer 2

Chromosomes condense down and become visible (supercoiling), as DNA wraps around histones. Centrioles migrate to opposite poles of cell and spindle forms. Homologous pairs come together to form bivalent (one maternal, one paternal). Non-sister chromatids wrap around eachother and attach at chiasmata (crossing over). Nucleolus disappears and nuclear envelope breaks down.

Question 3

Metaphase 1

Answer 3

Bivalents line up across the equator of spindle and attach to spindle fibres at their centromeres. Bivalents are arranged randomly with eachother facing opposite poles, which allows chromosmes to be independently segregated when pulled apart.

Question 4

Anaphase 1

Answer 4

Homologous chromosomes in each bivalent are pulled by spindle fibres to opposite poles. Centromeres don’t divide.Chiasmata seperate and lengths of chromatid that were crossed over remain with newly attached chromosomes.

Question 5

Telophase 1

Answer 5

Two new nuclear envelopes form, one around each set of chromosomes at each pole. The cell divides by cytokineses. In most plant cells, the cell goes straight from anaphase 1 into meiosis 2.

Question 6

Prophase 2

Answer 6

If a nuclear envelope has reformed, it breaks down again. The nucleolus disappears, chromosomes condense and spindles form.

Question 7

Metaphase 2

Answer 7

Chromosomes arrange themselves on the equator, attached to the spindle fibres at their centromeres. Chromatids of each chromosome are randomly assorted.

Question 8

Anaphase 2

Answer 8

Centromeres divide and chromatids are pulled to opposite poles by spindle fibres. The chromatids randomly segregate.

Question 9

Telophase 2

Answer 9

Nuclear envelope reforms around haploid daughter nuclei. In animals the two cells now divide to give four haploid cells. In plants, a tetrad of four haploid cells is formed.