A-Level · Biology · AQA · Mark scheme decoded

AQA A-Level Biology: Meiosis and Genetic Variation — mark scheme explained

Machine-verifiedchecked against the AQA A-Level Biology specificationlast verified 3 July 2026

The short answer

Meiosis is a specialized form of cell division that occurs in the germ-line (reproductive) cells found in the gonads of organisms to produce gametes. It gives rise to gametes; it is not a division of the gametes themselves.

The question

A cell with a chromosome content of 2n = 8 undergoes meiosis. Draw and label the chromosome content of the cells after the first and second meiotic divisions.

[Paraphrased for study — not reproduced from any exam paper.]

4 marks

Mark scheme, decoded

How the examiner actually awards the marks on this topic.

Gradora's own decode of the marking approach — not the exam board's published mark scheme.

How marks are awarded

For diagram questions, marks are typically awarded for correct labeling and accurate representation of the process. For explanation questions, marks are given for clear and concise descriptions that demonstrate a deep understanding of the topic. For comparison questions, marks are awarded for identifying both similarities and differences.

What the command words demand

Draw: Create a labeled diagram to illustrate a process or structure.
Explain: Provide a detailed description of the concept, including relevant principles and relationships.
Compare: Identify similarities and differences between two or more processes or structures.
Identify: Recognize and name specific components or stages in a process.

Model answer

A full-mark response to the question above, worked through step by step.

Timing: Allocate approximately 5-7 minutes per question to ensure you have enough time to carefully read the problem, draw or write your answers, and check your work.

Identify the initial chromosome content.0 marks
Initial chromosome content: 2n = 8 (4 pairs of homologous chromosomes), with each chromosome having been replicated to consist of 2 sister chromatids before division.
After meiosis I (the reduction division), homologous chromosomes separate.2 marks
Chromosome content after meiosis I: n = 4 (two cells, each with 4 chromosomes, but each chromosome still consists of 2 sister chromatids, as homologues have separated but chromatids have not). This halves the chromosome number from diploid to haploid.
After meiosis II, sister chromatids separate.2 marks
Chromosome content after meiosis II: n = 4 (four cells, each with 4 chromosomes that now consist of single chromatids, as sister chromatids have separated).

Final answer: After meiosis I: 2 cells, each n = 4, with each chromosome composed of 2 sister chromatids (meiosis I is the reduction division in which homologues separate). After meiosis II: 4 cells, each n = 4, with chromosomes now consisting of single chromatids (sister chromatids have separated). The diagram answer must show chromatid number, not just chromosome number.

Work through every step correctly and you earn all 4 marks.

Another worked example

Explain how independent assortment during meiosis contributes to genetic variation.

3 marks

Define independent assortment.1 mark
Independent assortment is the random alignment of homologous chromosomes at metaphase I during meiosis.
Explain the significance of this randomness.2 marks
This randomness means that each gamete can receive any combination of maternal and paternal chromosomes, leading to a vast number of possible genetic combinations in the offspring.

Final answer: Independent assortment is the random alignment of homologous chromosomes at metaphase I during meiosis. This randomness means that each gamete can receive any combination of maternal and paternal chromosomes, leading to a vast number of possible genetic combinations in the offspring.

Work through every step correctly and you earn all 3 marks.

Common mistakes

Confusing meiosis with mitosis in terms of chromosome content and number of daughter cells.
Why it happens: Students often mix up the outcomes of meiosis and mitosis, leading to incorrect answers about the number of daughter cells and their ploidy.
Fix: Always remember that meiosis results in four haploid daughter cells, while mitosis produces two diploid daughter cells.
Failing to understand the stages of meiosis and their significance.
Why it happens: Students may not fully grasp the importance of each stage, such as prophase I for crossing over or metaphase I for independent assortment.
Fix: Practice drawing and labeling the stages of meiosis, focusing on key events like crossing over and independent assortment.
Misunderstanding the concept of genetic variation from meiosis.
Why it happens: Students may not recognize how mechanisms like independent assortment and crossing over contribute to genetic diversity.
Fix: Review the processes of independent assortment and crossing over, and practice explaining their roles in generating genetic variation.
Confusing base substitution with base deletion mutations.
Why it happens: Students may mix up the definitions and effects of these two types of mutations.
Fix: Clearly define base substitution (replacement of one nucleotide) and base deletion (removal of one or more nucleotides), and practice identifying their potential impacts on protein function.
Failing to recognize the importance of random fertilization in genetic variation.
Why it happens: Students may overlook the role of random fertilization in combining genetic material from both parents.
Fix: Practice explaining how random fertilization contributes to genetic diversity by creating unique combinations of alleles in each zygote.
Not understanding the degenerate nature of the genetic code and its implications for mutations.
Why it happens: Students may not grasp how some base substitutions do not change the encoded amino acid due to the redundancy in the genetic code.
Fix: Review the concept of codon degeneracy and practice explaining how it can buffer against certain types of mutations.

Where the marks go

The question types you’ll meet on this topic and the marks each one carries — so you know what to expect and where to focus.

Question type	What you’re asked to do	Marks
Meiosis Chromosome Diagram	Draw and label chromosome content of cells after both meiotic divisions from a diploid start.	4
Explain Genetic Variation	Explain how random chromosome alignment in meiosis produces varied gamete combinations.	3
Explain Mutation Effect	Explain how a base substitution mutation might alter an enzyme's structure and therefore its function.	4
Explain Genetic Variation	Describe how random fertilisation combines gametes to increase genetic variation within a species.	3
Total across these question types		14

Question types and mark tariffs are Gradora’s guidance based on how this topic is typically examined — not the board’s official paper structure.