Stages of Meiosis

Explain the events of all stages of meiosis

• Meiosis I
• Prophase I
• Centrosome movement, spindle formation, nuclear envelope breaks down, chromosomes condense
• Chromosomes align with their homolog pair, and crossing over occurs [this is the exchange of DNA between two non-sister chromatids]
• The chiasmata is visible in this stage, this is the location where crossing over occurs
• Microtubules from the centrosomes will begin to attach to the kinetochores of the homologous chromosome pairs
• Metaphase I
• Pairs of homologous chromosomes are arranged at the metaphase plate
• Both chromatids of one homolog pair are attached to a spindle fiber on either polar side of the cell
• Anaphase I
• Homologs separate as proteins responsible for sister chromatid cohesion along the chromatid arms break down
• Homologs move towards opposite poles of the cell
• Sister chromatid stay connected to each other as they separate and move
• Telophase I and Cytokinesis
• Each half of cell now has a complete haploid set of duplicated chromosomes
• Cytokinesis divides cytoplasm and splits cell in half
• Meiosis II - NO CHROMOSOME DUPLICATION
• Prophase I
• Spindle apparatus forms
• Chromosomes begin to line up along the metaphase plate
• Metaphase I
• Microtubules attach to kinetochores and pull apart sister chromatids
• Anaphase I
• Chromosomes move up the microtubules towards opposite ends of the cell
• Telophase I and Cytokinesis
• Nuclei form, chromosomes begin to condense
• Cell divides

NOW, at the end of meiosis in an animal cell, the end result is four daughter cells [when starting with one cell]