What Happens in Meiosis 1?

During meiosis 1, a diploid cell's chromosomes segregate and produce four haploid cells. It is the completion of this phase that leads to genetic diversity.

Meiosis I takes place over six stages:

  1. Prophase I - the homologous chromosomes pair up and form synapses to become bivalents. As the genes recombine, chiasma form.
  2. Prometaphase I - the nuclear envelope disappears. Each chromosome gains a kinetochore and those attached to spindle fibers begin to move.
  3. Metaphase II - the bivalents containing two chromosomes align at the metaphase plate. How they align is random, which means that either parental homologue can end up on each side. As such, there's a 50 percent chance of the daughter cells inheriting the maternal or paternal homologue.
  4. Anaphase I - the chiasma separate and the chromosomes containing two chromatids move to separate poles. At this stage, the daughter cell is haploid, as it features two chromosomes.
  5. Telophase I - either the cell enters meiosis II or the nuclear envelope reforms.
  6. Citokinesis occurs - This means two complete daughter cells form.

Meiosis II involves a similar process, but the chromosomes no longer feature identical chromatids. During meiosis II the chromatids separate to create two daughter cells, each with 23 chromosomes. Unlike meiosis I, the chromosomes only have one chromatid.