alternation of haploid and diploid phases
generalized animal life cycle
Prophase I | the chromosomes wind up and become more compact; the nuclear envelope breaks down; the homologous chromosomes pair up; the homologous chromosomes may exchange pieces of chromosomes (called crossing over); the spindle begins to form; the chromosome pairs attach to the spindle fibers |
Metaphase I | the spindle fibers pull on the chromosome pairs until they are lined up at the center of the cell |
Anaphase I | the spindle fibers continue to pull on the chromosome pairs until the homologous chromosomes separate from one another and are pulled to the ends of the cells; other spindle fibers are pushing the two ends of the cell away from each other |
Telophase I | when the chromosomes are at opposite ends of the cell, they start to spread out again; the nuclear envelope re-forms; the spindle fibers disappear; cytokinesis begins |
Cytokinesis | |
Prophase II | the chromosomes wind up and become more compact, the nuclear envelope breaks down; the spindle begins to form; the chromosomes attach to the spindle fibers |
Metaphase II | the spindle fibers pull on the chromosomes until the chromosomes are lined up at the center of the cell |
Anaphase II | the spindle fibers continue to pull on the chromosomes until the DNA copies (chromatids) separate from one another and are pulled to the ends of the cells; other spindle fibers are pushing the two ends of the cell away from each other |
Telophase II | when the chromosomes are at opposite ends of the cell, they start to spread out again; the nuclear envelope re-forms; the spindle fibers disappear; cytokinesis begins |
Cytokinesis |
© Carol L. Wymer, 2004