Meiosis 1

Question 1

Prophase 1

Answer 1

1. Chromosomes condense and get shorter and fatter.
2. Homologous chromosomes pair up, forming bivalents.
3. Crossing over occurs.
4. Centrioles move to opposite sides and form spindle fibres. Nuclear envelope breaks down.

Question 2

Metaphase 1

Answer 2

1. Homologous pairs line up across the centre of the cell and attach to the spindle fibres by their centromeres.
2. Orientation of each homologous pair is random and independent of any other homologous pair.
3. Maternal and paternal chromosomes can end up facing either pole -> this is independent assortment.
   This results is many different combinations of alleles facing the poles.

Question 3

Anaphase 1

Answer 3

1. Homologous chromosomes are pulled to the opposite poles and the chromatids stay joined to each other.
2. Sections of DNA on sister chromatids, which became entangled during crossing over, now break off and re-join which can result in exchange of DNA.

Question 4

Telophase 1

Answer 4

1. Chromosomes assemble at each pole and nuclear membrane reforms.
2. Chromosomes uncoil.
3. Cell undergoes cytokinesis and divides in 2 haploid cells.