Mitosis vs Meiosis — MDCAT Biology Lesson

MDCAT Biology · curriculum topic: Cell Structure and Function / Reproduction

Learning objective

By the end of this lesson you should be able to state how mitosis and meiosis differ in the number of divisions, the number and type of daughter cells produced, and the stages at which genetic variation is introduced, and apply that comparison to practice MCQs.

How this comparison is usually tested

Questions on cell division are often phrased in a single line: a stage, a chromosome number or an outcome is named, and you decide whether it belongs to mitosis or meiosis. The two processes share several phase names, which is what makes them easy to mix up.

Three anchors keep them apart — how many divisions happen, what the daughter cells are like, and where genetic variation arises. Unless stated otherwise, the comparison below describes a typical diploid animal cell undergoing normal division, ignoring mutation and other abnormal events.

Mitosis: one division, two cells with the parent's chromosome number

One nuclear division following interphase: prophase, metaphase, anaphase, telophase.
Sister chromatids separate at anaphase, so each daughter cell receives a full copy of every chromosome.
Two daughter cells are produced, each with the same chromosome number as the parent cell and — apart from mutation or other abnormal events — genetically identical to it. Mitosis preserves the chromosome number rather than halving it, so a diploid cell gives diploid cells (2n → 2n) and a haploid cell, as in many fungi and in plant gametophytes, gives haploid cells (n → n).
Occurs in somatic cells for growth, tissue repair and replacement, and in asexual reproduction.

Meiosis: two divisions, four genetically distinct haploid cells

Two successive divisions — meiosis I and meiosis II — after a single round of DNA replication.
Meiosis I is the reduction division: homologous chromosomes separate, halving the chromosome number (2n → n).
Meiosis II resembles mitosis in mechanism: sister chromatids separate, but the cells are already haploid.
Four daughter cells are produced, each haploid and genetically distinct from the parent and from each other.
Occurs in germ cells to form gametes, keeping the chromosome number constant across generations after fertilisation.

Where the variation comes from

Two events in meiosis generate genetic variation. Crossing over happens in prophase I, when homologous chromosomes pair as bivalents and exchange segments at the chiasmata. Synapsis and crossing over are characteristic of prophase I of meiosis; they are not normal features of mitosis in this comparison.

Independent assortment follows from the random orientation of each homologous pair at the metaphase I plate; the pairs then segregate independently of one another at anaphase I. So if a question mentions chiasmata, bivalents, synapsis or a tetrad, it is pointing to meiosis I.

In human females the two meiotic divisions are unequal: the cytoplasm is divided unevenly, so one functional ovum and two or three polar bodies are formed rather than four equivalent functional gametes.

Worked example — tracking chromosome number

A human cell has 46 chromosomes. Compare the number and chromosome content of the cells produced if it divides by mitosis with those produced if it divides by meiosis.

Start with the diploid number: 2n = 46, so n = 23.
Mitosis: one division, two daughter cells. Chromosome number is conserved, so each daughter cell has 46 chromosomes and is genetically identical to the parent.
Meiosis I: homologous chromosomes separate, giving two cells with 23 chromosomes each — the reduction has already happened here.
Meiosis II: each of those two cells divides as sister chromatids separate, giving 2 × 2 = 4 cells, still with 23 chromosomes each.

Answer: Mitosis → 2 cells × 46 chromosomes, genetically identical. Meiosis → 4 cells × 23 chromosomes, genetically distinct.

Practice questions

Question 1. How many daughter cells are produced from a single cell completing meiosis?

A. Two
B. Three
C. Four
D. Eight

Answer: C. Four — Meiosis involves two successive divisions after one round of DNA replication, so one parent cell yields four haploid daughter cells.

Question 2. Crossing over between homologous chromosomes occurs during:

A. Prophase of mitosis
B. Prophase I of meiosis
C. Metaphase II of meiosis
D. Telophase of mitosis

Answer: B. Prophase I of meiosis — Homologous chromosomes pair (synapsis) in prophase I, where chiasmata form and segments are exchanged. Synapsis and crossing over are characteristic of prophase I of meiosis; they are not normal features of mitosis in this comparison.

Question 3. Which event distinguishes anaphase I of meiosis from anaphase of mitosis?

A. Sister chromatids separate
B. Homologous chromosomes separate while sister chromatids stay joined
C. The nuclear envelope reforms
D. Chromosomes replicate

Answer: B. Homologous chromosomes separate while sister chromatids stay joined — In anaphase I whole homologous chromosomes are pulled to opposite poles with their sister chromatids still attached at the centromere. Sister chromatids separate in mitotic anaphase and in anaphase II.

Question 4. A somatic human cell (2n = 46) divides by mitosis. Each daughter cell contains:

A. 23 chromosomes
B. 46 chromosomes
C. 92 chromosomes
D. A variable number

Answer: B. 46 chromosomes — Mitosis preserves the chromosome number: each daughter cell receives one copy of every chromosome, so 46 chromosomes, and in normal division it is genetically identical to the parent.

Question 5. Meiosis I is described as the reduction division because:

A. The cell becomes smaller
B. The chromosome number is halved
C. DNA replication is reduced by half
D. Only half the spindle fibres form

Answer: B. The chromosome number is halved — Separation of homologous chromosomes in meiosis I takes the cell from diploid (2n) to haploid (n). Meiosis II then separates sister chromatids without changing the chromosome number again.

Common mistakes

Saying meiosis halves the chromosome number in meiosis II. The reduction happens in meiosis I; meiosis II only separates sister chromatids.
Treating synapsis and chiasmata as features of mitosis. Homologous pairing and crossing over are characteristic of prophase I of meiosis, not of normal mitosis.
Reading "four daughter cells" as "four divisions". There are two divisions producing four cells.
Forgetting that DNA replication happens once, in interphase before meiosis I — not again between the two meiotic divisions.

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