AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), 2023: Question 6
11 marks · Standard Demand difficulty · Short Answer
Identify the type of cell division for gametes, explain variation in sexual reproduction, define genetic terms, and calculate the probability of inheriting polydactyly using a Punnett square.
Practise this questionQuestion
Question text
06 Sexual reproduction in humans involves the production of egg cells and sperm cells.
06.1 Name the type of cell division that produces egg cells and sperm cells.
[1 mark]
06.2 Sexual reproduction produces offspring that are genetically different from each other.
Give two reasons why sexual reproduction causes variation in the offspring.
[2 marks]
Polydactyly is an inherited disorder.
The allele for polydactyly is dominant, D.
A person with two copies of the allele d will not have polydactyly.
06.3 A person with the genotype DD is homozygous.
What word describes the genotype Dd?
[1 mark]
06.4 A person with the genotype Dd and a person with the genotype dd plan to have
a child.
Determine the probability that the child will have polydactyly.
You should:
• complete the Punnett square diagram
*27* • identify any offspring genotype that would have polydactyly.
[5 marks]
Probability that the child will have polydactyly =29
06.5 Embryos can be screened for the alleles that cause inherited disorders.
Give two advantages of embryo screening.
[2 marks]
Mark scheme
Show the mark scheme
Question 6
AO /
Question Answers Extra information Mark
Spec. Ref.
06.1 meiosis allow phonetic spelling 1 AO1
4.6.1.1
4.6.1.2
AO /
Spec. Ref.
06.2 gametes / eggs / sperm are not allow gametes / eggs / sperm 1 AO1
(genetically) identical are (genetically) different 4.6.1.1
allow cells produced by meiosis 4.6.1.2
are not (genetically) identical
(there is) mixing of genetic allow genetic information / 1
information / genes genes / DNA from each parent
/ DNA ignore gametes fuse unqualified
or
genetic information / genes / ignore two parents unqualified
DNA from two / both parents
if no other mark awarded allow 1
mark for mutations
AO /
Spec. Ref.
06.3 heterozygous ignore dominant / recessive 1 AO2
4.6.1.4
AO /
Spec. Ref.
06.4 (parents gamete genotypes allow in either position in 1 AO2
shown) Punnett square
D d and d d
(possible offspring genotypes allow correct derivation of 2 AO2
correctly derived) offspring genotypes from
Dd Dd dd dd incorrect gametes 19
allow 3 correct offspring
genotypes for 1 mark
correct identification of Dd if derivation not correct and 1 AO2
offspring as having polydactyly shows DD and Dd, both must be
identified as having polydactyly
probability must match derived if no derivation shown allow 0.5 1 AO3
offspring genotypes or 50% or 1 in 2 or
1:1 or ½
do not accept 1:2 4.6.1.4
allow correct probability from 4.6.1.5
incorrectly derived offspring
AO /
Spec. Ref.
06.5 any two from: 2 AO3
• can find out if the embryo has allow can find out if the embryo 4.6.1.5
an (inherited) disorder has inherited disease
ignore can find out if the embryo
has disease(s)
• can prepare for baby (with the allow description of preparation
disorder) for the baby eg access to early
treatment
• can decide whether to allow choice of (in vitro)
continue with the pregnancy embryos (to be implanted)
• fewer people with (inherited)
disorders over time
Total Question 6 11
How to answer it
Sexual Reproduction & Inherited Disorders
What this question tests
This question assesses your understanding of meiosis, the causes of genetic variation, use of genetic terminology (heterozygous), and your ability to predict inheritance using Punnett squares. It also touches on the practical and ethical benefits of embryo screening.
Cell Division for Gametes
Correct Answer
meiosis
Exam Technique
Be careful with spelling! Students often confuse mitosis (for growth) and meiosis (for gametes). While examiners allow phonetic spelling, getting the "e" and "i" in the right place is best practice.
Causes of Variation
Correct Answer
- Gametes (eggs/sperm) are genetically different from each other.
- There is a mixing of genetic information (DNA) from two parents.
Common Errors
Do not just say "there are two parents." You must explain that their genetic information mixes or that the gametes themselves are not identical.
Genetic Terminology
Key Knowledge
- Homozygous: Two of the same alleles (e.g., DD or dd).
- Heterozygous: Two different alleles (e.g., Dd).
Correct Answer
heterozygous
Predicting Inheritance (Punnett Square)
The Cross: Dd (Parent 1) x dd (Parent 2)
Step-by-Step Calculation
- Identify Parent Gametes: One parent is D and d . The other is d and d .
- Fill the Grid: Combine the letters in the boxes.
- Identify Phenotypes: Polydactyly is dominant (D). Any child with a capital D will have the disorder.
- Calculate Probability: Count the affected boxes out of 4.
The Completed Square
| d | d | |
| D | Dd | Dd |
| d | dd | dd |
Highlighted cells = Child has polydactyly.
Probability: 0.5, 50%, or 1 in 2.
Examiner Insight
To get full marks (5 marks!), you must:
1. Put the correct parent alleles on the outside.
2. Fill all 4 inside boxes correctly.
3. Clearly identify which genotypes result in polydactyly (Dd).
4. State the probability. Note: Do not write "1:2" for probability; use 0.5, 50%, or 1/2.
Advantages of Embryo Screening
Key Advantages (Pick Two)
- Can find out if the embryo has an inherited disorder.
- Allows parents to prepare (e.g., arrange medical treatment or support).
- Allows parents to decide whether to continue with the pregnancy.
- Reduces the number of people with the disorder in the population over time.
Common Errors
Avoid vague answers like "it makes the baby healthy." Screening only identifies the condition; it doesn't cure it. Also, ensure you focus on advantages as requested, not the ethical disadvantages.
Topics
Biology · B6: Inheritance, Variation and Evolution
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.