--- title: "Anaphase — AP Bio Definition & Exam Guide" description: "Anaphase is the stage where chromosomes get pulled to opposite poles by spindle fibers. Learn how it differs in mitosis vs. meiosis I for AP Bio." canonical: "https://fiveable.me/ap-bio/key-terms/anaphase" type: "key-term" subject: "AP Biology" unit: "Unit 4" --- # Anaphase — AP Bio Definition & Exam Guide ## Definition Anaphase is the stage of cell division, after metaphase, when spindle fibers pull chromosomes toward opposite poles of the cell. In mitosis and meiosis II, sister chromatids separate; in meiosis I (anaphase I), whole homologous chromosomes separate while sister chromatids stay together. ## What It Is Anaphase is the "pulling apart" step of [cell division](/ap-bio/key-terms/cell-division "fv-autolink"). [Spindle fibers](/ap-bio/unit-4/homeostasis-feedback-loops/study-guide/OgMSpwCrEez0qyWtlCAC "fv-autolink") attached to the chromosomes shorten and drag genetic material toward opposite ends (poles) of the cell. By the time anaphase ends, both halves of the cell have a complete, matching set of chromosomes ready to become two new nuclei. Here's the catch that [AP Bio](/ap-bio "fv-autolink") loves: *what* gets pulled apart depends on the division. In **mitosis** and **meiosis II**, sister chromatids split at the centromere and move to opposite poles. In **meiosis I (anaphase I)**, the sister chromatids stay glued together, and instead the whole **homologous pairs** separate. That single difference is why meiosis cuts the chromosome number in half (diploid to haploid) while mitosis keeps it the same. ## Why It Matters Anaphase lives in two places on the CED. In [Unit 5](/ap-bio/unit-5 "fv-autolink") (Heredity), it's part of the meiosis sequence under **AP Bio 5.1.A**, which asks you to explain how meiosis passes chromosomes from one generation to the next, and **AP Bio 5.1.B**, which asks you to compare the phases of [mitosis](/ap-bio/key-terms/mitosis "fv-autolink") and meiosis. In Unit 4 (Cell Communication and Cell Cycle), the orderly progression that includes anaphase is what cell-cycle checkpoints (**AP Bio 4.6.A**) protect. If a cell rushes into anaphase before chromosomes are properly attached, you get unequal distribution, which ties into the disruptions in **AP Bio 4.6.B** that can lead to cancer or apoptosis. The big theme is information transfer: anaphase is the physical moment when genetic information is split into the next cells. ## Connections ### [Anaphase I (Unit 5)](/ap-bio/key-terms/anaphase-i) [Anaphase I](/ap-bio/key-terms/anaphase-i "fv-autolink") is the meiosis version where homologous chromosomes separate but sister chromatids stay attached. Regular anaphase (mitosis and meiosis II) separates the sister chromatids themselves. Mixing these up is the single most common AP error here. ### [Sister Chromatids (Unit 5)](/ap-bio/key-terms/sister-chromatids) [Sister chromatids](/ap-bio/key-terms/sister-chromatids "fv-autolink") are the two identical copies joined at the centromere. Whether they split or stay together during anaphase is the whole story: split in mitosis/meiosis II, stuck together in anaphase I. ### Cell Cycle Checkpoints (Unit 4) The spindle checkpoint is basically the bouncer that won't let a cell enter anaphase until every [chromosome](/ap-bio/key-terms/chromosome "fv-autolink") is correctly attached to the spindle. No proper attachment means no anaphase, which prevents daughter cells from getting the wrong number of chromosomes. ### [Cytokinesis (Unit 4)](/ap-bio/key-terms/cytokinesis) Anaphase separates the chromosomes; cytokinesis splits the actual cell. Anaphase sets up where the two new nuclei will go, and cytokinesis (via a cleavage furrow in animals or a cell plate in plants) finishes the job by dividing the cytoplasm. ## On the AP Exam You'll most often see anaphase in MCQ stems that describe what a cell looks like and ask you to identify the stage or the process. A classic move: a cell has "homologous chromosomes moving to opposite poles, but sister chromatids remaining attached at their centromeres" is anaphase I of meiosis, not regular anaphase. Watch for that exact wording. Another common stem asks what mechanism mitosis and meiosis I share during anaphase (answer: the spindle apparatus pulling chromosomes to opposite poles, per AP Bio 5.1.B). On FRQs, anaphase shows up inside meiosis or spindle questions. The 2025 Short FRQ Q6 used the ald gene tied to centromeres and meiotic spindle filaments, exactly the machinery that drives anaphase. Be ready to explain what happens if that machinery fails: chromosomes don't separate evenly. ## Anaphase vs Anaphase I (meiosis) Plain anaphase (mitosis and meiosis II) splits sister chromatids at the centromere, so each pole gets one chromatid. Anaphase I keeps sister chromatids stuck together and separates the homologous pairs instead. If the question says sisters stay attached, it's anaphase I. ## Key Takeaways - Anaphase is the stage where spindle fibers pull chromosomes toward opposite poles of the cell. - In mitosis and meiosis II, sister chromatids separate; in anaphase I of meiosis, homologous pairs separate while sister chromatids stay joined. - The separation of homologs in anaphase I is why meiosis reduces the chromosome number from diploid to haploid. - The spindle apparatus is the shared mechanism that moves chromosomes in both mitosis and meiosis I (AP Bio 5.1.B). - A spindle checkpoint blocks entry into anaphase until chromosomes are properly attached, protecting against errors (AP Bio 4.6.A). - Anaphase separates the genetic material, but cytokinesis is what actually splits the cell into two. ## FAQs ### What happens during anaphase in AP Bio? Spindle fibers shorten and pull chromosomes toward opposite poles of the cell. In mitosis and meiosis II this separates sister chromatids; in anaphase I of meiosis it separates homologous chromosome pairs. ### Do sister chromatids separate in anaphase I? No. In anaphase I, sister chromatids stay attached at the centromere and the homologous chromosomes get pulled apart instead. Sister chromatids don't separate until anaphase II (or regular anaphase in mitosis). ### How is anaphase different from anaphase I? Anaphase (mitosis and meiosis II) splits sister chromatids so each pole gets one chromatid. Anaphase I (meiosis I) keeps sisters together and separates whole homologous pairs, which is the step that halves the chromosome number. ### Is anaphase on the AP Bio exam? Yes. It shows up in Unit 5 meiosis questions and Unit 4 cell-cycle questions. MCQs often describe chromosome behavior and ask you to identify the stage, and FRQs may test the spindle machinery that drives separation. ### Why does anaphase matter for genetic inheritance? Anaphase is the physical moment genetic information is divided into the next cells (AP Bio 5.1.A). If chromosomes separate unevenly, daughter cells end up with the wrong number, which connects to cell-cycle disruptions in AP Bio 4.6.B. ## Related Study Guides - [4.6 Regulation of the Cell Cycle](/ap-bio/unit-4/cell-cycle/study-guide/4ztGMFvp0v4KAzL65pOP) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/ap-bio/key-terms/anaphase#resource","name":"Anaphase — AP Bio Definition & Exam Guide","url":"https://fiveable.me/ap-bio/key-terms/anaphase","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/ap-bio/key-terms/anaphase#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-06-12T22:53:00.052Z","isPartOf":{"@type":"Collection","name":"AP Biology Key Terms","url":"https://fiveable.me/ap-bio/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/ap-bio/key-terms/anaphase#term","name":"Anaphase","description":"Anaphase is the stage of cell division, after metaphase, when spindle fibers pull chromosomes toward opposite poles of the cell. 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