meiosis I in live mouse oocyte

Microtubules: green

Chromosomes: red

Movie recorded by Melina Schuh

 

1. Nucleus breaks down.

2. Acentrosomal spindle assembles in oocyte's centre.

3. Chromosome bivalents become aligned in metaphase plate.

4. Spindle relocates to oocyte's surface.

5. Homologous chromosomes segregate.

6. Half of the chromosomes are eliminated in the first polar body.

7. Second half is aligned in metaphase II spindle.

8. Egg is now haploid and ready for fertilization.