Meiosis II is the second division of meiosis, where sister chromatids of each chromosome separate (just like in mitosis), turning the two haploid cells from meiosis I into four haploid gamete cells.
Meiosis II is the second round of division in meiosis, and it happens after meiosis I has already cut the chromosome number in half. So you start meiosis II with two cells that are already haploid, each chromosome still made of two sister chromatids stuck together at the centromere. Meiosis II then pulls those sister chromatids apart.
If that sounds familiar, it should. Meiosis II is basically mitosis happening in a haploid cell. It runs through prophase II, metaphase II, anaphase II, and telophase II. The big payoff comes in anaphase II, when sister chromatids finally split and move to opposite poles. By the end you have four haploid cells, each with single-chromatid chromosomes. This is the step that finishes building gametes (EK 5.1.A.1).
Meiosis II lives in Unit 5: Heredity, under Topic 5.1 Meiosis. It supports two learning objectives: AP Bio 5.1.A (how meiosis transmits chromosomes to the next generation) and AP Bio 5.1.B (comparing the phases and outcomes of mitosis and meiosis). The whole point of meiosis is making haploid gametes so that fertilization restores the diploid number, and meiosis II is the division that delivers the final four cells. On the exam you're often asked to track chromosome number and DNA content across the two divisions, so knowing exactly what meiosis II does (separates sisters, not homologs) is the difference between a right and wrong answer.
Keep studying AP Biology Unit 5
Meiosis I (Unit 5)
Meiosis I separates homologous chromosomes; meiosis II separates sister chromatids. Think of it as two cuts: the first reduces the number of chromosomes (diploid to haploid), the second splits the doubled chromosomes into singles. Mixing up which division does which is the most common meiosis mistake.
Mitosis (Unit 4)
Meiosis II is essentially mitosis in a haploid cell. Both use a spindle to pull sister chromatids apart and both keep the chromosome number the same from start to finish. The difference is that meiosis II's starting cell is already haploid, so the result is gametes, not body cells (EK 5.1.B.1).
Anaphase II (Unit 5)
Anaphase II is the moment meiosis II actually does its job. Sister chromatids separate at the centromere and head to opposite poles. This is your cue on an MCQ: if sisters are splitting, you're in anaphase II (or mitotic anaphase), not anaphase I.
Chromosome Segregation (Unit 5)
Proper segregation in both meiotic divisions is what gives each gamete the correct, complete set of chromosomes. Errors here lead to gametes with too many or too few chromosomes, which connects forward to inheritance patterns and genetic disorders later in Unit 5.
Meiosis II shows up most in MCQs that ask you to identify a stage from a description or track DNA and chromosome content. A classic stem describes a cell where "homologous chromosomes move to opposite poles but sister chromatids stay attached" and asks where it is. That's anaphase I, not meiosis II, and the trap is answering meiosis II. Another common question gives you 2n=16 and asks the chromosome composition right after meiosis I but before meiosis II, where each cell is haploid (8 chromosomes) but each chromosome still has two chromatids. On FRQs, meiosis II usually appears inside a larger meiosis question. The 2022 and 2024 released FRQs both center on crossing over in meiosis I, so you may need to explain how the genetic variation set up earlier gets distributed into the four final cells once meiosis II finishes. Be ready to compare meiosis II directly to mitosis (LO 5.1.B).
Meiosis I separates homologous chromosomes and reduces the cell from diploid to haploid (this is the reductional division). Meiosis II separates sister chromatids and keeps the cell haploid the whole time (this is the equational division, just like mitosis). Quick test: if the chromosome number drops, it's meiosis I; if sisters split apart, it's meiosis II.
Meiosis II separates sister chromatids, while meiosis I separates homologous chromosomes.
Cells entering meiosis II are already haploid, so meiosis II does not reduce the chromosome number further.
Meiosis II is mechanically just like mitosis, but it acts on haploid cells and produces gametes.
Sister chromatids split at the centromere during anaphase II, finishing the four-cell result of meiosis.
One diploid cell yields four haploid gamete cells by the end of meiosis II (LO 5.1.A).
Meiosis II takes the two haploid cells made in meiosis I and separates their sister chromatids, producing four haploid cells total. It runs through prophase II, metaphase II, anaphase II, and telophase II, with sister chromatids splitting during anaphase II.
No. The chromosome number is cut in half during meiosis I, not meiosis II. Cells already enter meiosis II as haploid, so meiosis II just separates sister chromatids and keeps the haploid number the same, which is why it's called the equational division.
Meiosis I separates homologous chromosome pairs and turns one diploid cell into two haploid cells. Meiosis II separates sister chromatids and turns those two haploid cells into four. If the chromosome count drops, you're in meiosis I; if sisters split, you're in meiosis II.
Mechanically they're nearly identical, since both separate sister chromatids using a spindle and keep the chromosome number constant. The difference is that meiosis II happens in a haploid cell and produces gametes, while mitosis happens in diploid cells and produces identical body cells (EK 5.1.B.1).
It's haploid but each chromosome still has two sister chromatids attached at the centromere. For a 2n=16 organism, each cell would have 8 chromosomes, each made of two chromatids, going into meiosis II.