AP Syllabus focus:
‘Both mitosis and meiosis use a spindle apparatus but produce different numbers of daughter cells with different genetic content.’
Mitosis and meiosis are related cell-division programs that handle chromosomes differently.
Side-by-side schematic comparing mitosis and meiosis, emphasizing the number of divisions and the resulting number of daughter cells. The labels highlight how meiosis involves two successive divisions to generate four haploid products, whereas mitosis produces two genetically identical daughter cells. Source
Comparing their shared mechanics and distinct outcomes clarifies how organisms grow and repair tissues versus generate gametes for sexual reproduction.
Core similarities: shared division machinery
Both processes rely on the spindle apparatus to move chromosomes accurately and ensure each new cell receives the appropriate chromosomal material.
Spindle apparatus: A dynamic microtubule-based structure (plus associated proteins) that attaches to chromosomes and segregates them to opposite poles during cell division.
Key shared features include:
Diagram of mitosis stages (including spindle formation and chromosome alignment), illustrating how microtubules attach to kinetochores and generate tension prior to separation. This visual reinforces why metaphase alignment is a checkpoint-like moment: correct bi-orientation helps ensure accurate segregation of sister chromatids. Source
Chromosome condensation to prevent tangling and breakage during movement.
Spindle microtubules attaching to chromosomes (via kinetochores) and generating tension.
A metaphase alignment step that helps verify proper attachment before separation.
Cytokinesis following nuclear division to partition the cytoplasm into separate cells.
What is being separated: the main conceptual difference
Mitosis separates sister chromatids
In mitosis, the cell separates sister chromatids (identical DNA copies made during S phase) so that each daughter cell receives one copy of every chromosome.
Meiosis separates homologs, then sister chromatids
Meiosis is two sequential divisions:
Labeled sequence of meiosis I and meiosis II stages, showing the key shift in what separates across the two divisions. The figure makes it easy to track how homologous chromosomes segregate in meiosis I, followed by sister chromatid separation in meiosis II, leading to four haploid cells. Source
Meiosis I separates homologous chromosomes (one maternal, one paternal version of the same chromosome).
Meiosis II separates sister chromatids, similar to mitosis, but starting from haploid cells created in meiosis I.
Comparing phases: parallels and mismatches
“Prophase-like” events
Mitosis (prophase/prometaphase):
Chromosomes condense; spindle forms; nuclear envelope breaks down.
Spindle attaches so each chromatid is oriented toward opposite poles (bi-orientation).
Meiosis (overall):
Spindle forms in both divisions, but attachments differ:
In meiosis I, the spindle organizes to pull homologs apart (chromatids of a homolog typically move together).
In meiosis II, attachments resemble mitosis, separating chromatids.
Metaphase alignment
Mitosis metaphase:
Individual replicated chromosomes line up; each chromosome’s sister chromatids face opposite poles.
Meiosis metaphase:
In meiosis I, homologous pairs align as units (two homologs together).
In meiosis II, chromosomes align individually, comparable to mitosis.
Anaphase separation
Mitosis anaphase:
Sister chromatids separate; each becomes an individual chromosome at the poles.
Meiosis anaphase:
Meiosis I: homologous chromosomes separate (chromosome number is reduced).
Meiosis II: sister chromatids separate (no further reduction in chromosome number).
Telophase and cytokinesis
Mitosis: typically yields two nuclei, then cytokinesis produces two daughter cells.
Meiosis: cytokinesis after each division ultimately produces four daughter cells.
Outcomes: number of cells, ploidy, and genetic content
Cell number and ploidy
Mitosis outcome: 1 division → 2 daughter cells.
Maintains chromosome number (e.g., diploid stays diploid).
Meiosis outcome: 2 divisions → 4 daughter cells.
Reduces chromosome number (diploid → haploid), a key requirement for sexual life cycles.
Genetic similarity versus difference
Mitosis: daughter cells are genetically identical to each other and to the parent cell (barring mutation), supporting stable growth and tissue maintenance.
Meiosis: daughter cells differ in genetic content, because homologous chromosomes (maternal vs paternal) are sorted into different cells across the two divisions, producing distinct chromosome combinations in gametes.
Functional roles in organisms
Mitosis supports:
Growth, development, and cellular replacement.
Asexual reproduction in some eukaryotes.
Meiosis supports:
Production of gametes (or spores, depending on the life cycle).
Transmission of one chromosome set per gamete so fertilisation can restore diploidy.
FAQ
Meiosis includes a first division in which homologous chromosomes are segregated into different cells.
Mitosis does not pair or separate homologs as a set; it separates sister chromatids, which preserves the original chromosome number.
In mitosis, sister chromatids typically attach to opposite poles (bi-orientation).
In meiosis I, the arrangement favours separation of homologous chromosomes, with sister chromatids of the same homolog tending to move together to one pole.
Look for homologous chromosomes positioned as paired units at the metaphase plate, rather than single chromosomes aligned independently.
This indicates separation of homologs is about to occur.
No. Animals often form a cleavage furrow, while plants form a cell plate.
However, the key comparison for AP Biology is that mitosis has one cytokinesis event, whereas meiosis has two.
Chromosome number refers to how many sets (haploid vs diploid).
Genetic content refers to which versions of chromosomes and alleles are present; cells can share the same number of chromosomes yet differ in which maternal/paternal chromosomes they carry.
Practice Questions
State two differences between mitosis and meiosis in terms of outcomes. (2 marks)
Mitosis produces two daughter cells; meiosis produces four daughter cells. (1)
Mitosis maintains chromosome number (e.g. diploid to diploid) whereas meiosis halves it (diploid to haploid). (1)
Explain how spindle function is similar in mitosis and meiosis, but leads to different genetic outcomes. (5 marks)
Both use a spindle apparatus made of microtubules to attach to chromosomes and move them to opposite poles. (1)
In mitosis, sister chromatids are bi-oriented and separated in one division, producing genetically identical daughter cells. (2)
In meiosis, division I separates homologous chromosomes (reduction to haploid), changing the chromosome set in each cell. (1)
Division II separates sister chromatids, producing four haploid cells with different genetic content due to different combinations of maternal and paternal chromosomes. (1)
