Meiosis I One diploid nucleus to two haploid nuclei

Comparative summary of key features of
mitosis and meiosis, starting with a diploid cell. Only two paternal
and two maternal chromosomes are shown, for clarity. Mitosis maintains
the parental chromosome number. Meiosis halves it, to the
haploid number.

   Prophase I
• Chromosomes condense.
• Homologous chromosomes pair.
• Crossovers occur (not shown).
• Spindle forms and attaches chromosomes to spindle poles.
• Nuclear envelope breaks up.


   Metaphase I
• Chromosomes align midway between spindle poles.

   Anaphase I
• Homologous chromosomes separate and move toward at spindle poles.

   Telophase I
• Chromosome clusters arrive opposite spindle poles.
• New nuclear envelopes form.
• Chromosomes decondense.