AQA AS Level Biology Paper 2, June 2022: Question 4

8 marks · Medium difficulty · Short Answer

Describe meiosis, calculate expected chromosome arrangements due to independent segregation, draw gamete chromosomes, and identify a cell division process from a fungus life cycle.

Practise this question

Question

A four-part question about meiosis and the fungal life cycle. Question 04.1 asks to describe how meiosis results in haploid cells without variation (4 marks). Question 04.2 provides Figure 2 showing 4 homologous pairs of chromosomes and asks to calculate how many out of 300 cells have an identical chromosome arrangement due to independent segregation (2 marks). Question 04.3 asks to draw a diagram of chromosomes in one gamete produced from the cell in Figure 2 (1 mark). Question 04.4 shows Figure 3 (a fungus life cycle) and asks to identify the process shown by arrow A using tick boxes (1 mark).
Question text

04.1 Describe how the process of meiosis results in haploid cells.

Do not include descriptions of how genetic variation is produced in meiosis.

[4 marks]

04.2 Figure 2 shows the arrangement of chromosomes in a cell during the first meiotic

division.

Figure 2

A scientist observed 300 cells. All of the cells were at exactly the same stage of

meiosis as the cell shown in Figure 2.

Use your knowledge of the independent segregation of homologous chromosomes to

calculate how many of these cells are expected to have an identical arrangement of

chromosomes to those shown in Figure 2. Assume no crossing over occurs.

[2 marks]

Answer

04.3 Draw a diagram to show the chromosomes in one gamete produced by meiosis from

the cell shown in Figure 2.

[1 mark]

04.4 Figure 3 shows the life cycle of a fungus. The life cycle includes sexual reproduction.

Figure 3

What is the name of the process shown by arrow A in Figure 3?

Tick ( ) one box.

[1 mark]

Binary fission

Fertilisation

Meiosis

Mitosis

Mark scheme

Show the mark scheme The mark scheme details points for 04.1 including DNA replication, two divisions, separation of homologous chromosomes then sister chromatids, and 4 haploid cells. For 04.2, the answer is 18 to 19 cells based on probability calculations. For 04.3, a diagram showing 4 single chromosomes with correct shading (one from each homologous pair) is required. For 04.4, the correct tick is for Mitosis.

Question Marking Guidance Mark Comments

1. DNA replication (during late interphase);

2. Two divisions; 2. Accept for ‘two

divisions’, meiosis I

and meiosis II OR

3. Separation of homologous chromosomes (in examples of

first division); stages, e.g.

anaphase I and

anaphase II

4. Separation of (sister) chromatids (in second

division); 2. Accept description

that clearly indicates

two divisions

5. Produces 4 (haploid) cells/nuclei;

Ignore references to

4 max stage names (except

04.1

(4 x AO1) above)

2, 3. and 4. Accept

annotated

diagrammatic

representations

3 and 4. Reject

‘diploid cells’ once.

4. Accept

‘chromosomes’ for

‘chromatids’ but

reject homologous

chromosomes

5. Accept ‘gametes’

for cells

Correct answer for 2 marks, 18–19;;

Accept for 1 mark,

41 2

0.06–0.07 / (½) / (correct probability)

04.2 16

(2 x AO2)

OR

16 (correct number of arrangements);

Accept chromosomes

in any order

Reject evidence of 2

1 chromatids per

04.3 chromosome

(AO2)

Four chromosomes shaded correctly;

Mitosis; 1

04.4

(AO2)

How to answer it

Meiosis, Independent Segregation and Life Cycles

What this question tests

This exam question assesses your core knowledge of the stages of meiosis, how chromosome reduction leads to haploid cells, application of the independent segregation formula (2ⁿ) to calculate probability and expected frequencies, interpreting visual chromosome arrangements, and identifying cellular division types from organism life cycle diagrams.

Question 04.1 (4 Marks)

Describe how the process of meiosis results in haploid cells. (Do not include genetic variation)

✅ Correct Answer / Mark Scheme

  • Point 1: DNA replication occurs during late interphase (prior to division).
  • Point 2: Undergoes two separate nuclear/cell divisions (Meiosis I and Meiosis II).
  • Point 3: Homologous chromosomes separate during the first nuclear division.
  • Point 4: Sister chromatids separate during the second nuclear division.
  • Point 5: Produces a total of 4 haploid cells (or nuclei).

💡 Key Knowledge

  • Haploid cells contain a single set of unpaired chromosomes (half the diploid number, n ).
  • Emphasise the sequence: interphase replication ➔ 1st division (homologous pairs separate) ➔ 2nd division (chromatids separate).

🧠 Exam Technique

  • Read the stem carefully: "Do not include descriptions of how genetic variation is produced". Mentioning crossing over or random fertilisation will block your access to full marks.
  • Keep stage names explicit (anaphase I / anaphase II) to anchor your sequential description clearly for the examiner.

❌ Common Errors

  • Confusing the separation of homologous chromosomes with sister chromatids. Homologous pairs separate in division 1; chromatids separate in division 2.
  • Stating that "diploid cells" are produced at any point after the first division.
Max 4 marks available (4 × AO1)
Question 04.2 (2 Marks)

Calculate expected number of cells with an identical chromosome arrangement (300 cells total, Figure 2 has 4 homologous pairs).

✅ Correct Answer

18 or 19 (Accept exact unrounded fraction/probability or working steps leading to these values)

📐 Step-by-Step Calculation

  1. Step 1: Determine number of homologous pairs ( n ). Counting Figure 2 reveals n = 4 pairs.
  2. Step 2: Calculate total possible arrangements. Use formula 2ⁿ = 2⁴ = 16 possible arrangements.
  3. Step 3: Calculate individual probability. Probability of any single specific arrangement is 1/16 (or 0.0625).
  4. Step 4: Scale up to the sample size. Multiply probability by total observed cells: (1 / 16) × 300 = 18.75 cells.
  5. Step 5: Handle whole biological units. Since cells cannot be fractions, round to the nearest whole integer: 18 or 19.

🧠 Exam Technique & Guidance

  • Award of 2 marks is given for the correct final answer (18 or 19).
  • 1 mark is safely awarded for working out the correct probability ( 1/16 or 0.06 - 0.07 ) or stating the number of arrangements (16) if the final calculation slips up. Always show your full working out!

❌ Common Calculation Traps

  • Forgetting to multiply by 300 total cells and leaving the answer as a probability fraction ( 1/16 ).
  • Leaving the answer as 18.75 without rounding to a whole number of cells.
2 marks available (2 × AO2)
Question 04.3 (1 Mark)

Draw a diagram to show chromosomes in one gamete produced by meiosis from Figure 2.

✅ Correct Answer Structure

  • A circle representing a single gamete cell containing 4 single, un-replicated chromosomes (one from each homologous pair shown in Figure 2, maintaining correct shading/size variety).
  • Must show a mix of shaded/unshaded variants to reflect independent segregation, but crucially must feature single lines/chromosomes rather than sister-chromatid X-shapes.

❌ Common Errors to Avoid

  • Drawing X-shaped chromosomes (two chromatids per chromosome). Gametes produced after the second meiotic division contain single chromatid structures.
  • Drawing the wrong total chromosome number (e.g., drawing 8 individual lines instead of 4).
1 mark available (1 × AO2)
Question 04.4 (1 Mark)

Name the process shown by arrow A in Figure 3 (Diploid spores to mature zygote / growth phase).

✅ Correct Answer

Mitosis (Tick the Mitosis box)

💡 Key Knowledge

Growth, repair, and asexual development within life cycles (going from spore structures to multicellular structures without changing ploidy level) are always driven by mitosis, not meiosis or binary fission (which applies to prokaryotes).

1 mark available (1 × AO2)

Topics

Biology · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA AS Level Biology examination, Paper 2, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.