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Q 1-6: The diagram shows the stages in sexual reproduction in humans.
4. In which organs does meiosis occur in males and females?
5. At which stage in the diagram above does fertilisation occur?
8+9: Use this genetic diagram to complete the next two questions:
8. Using the information above, which one of the four individuals (i-iv) in the table below has the correct phenotype and genotype?
10. A 4 year old girl has a twin brother.
Which of the following statements is not correct?
Question 1:
A. 46
Reasoning: Human body (somatic) cells, such as cheek cells, contain 46 chromosomes (23 pairs). This includes 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females, XY in males).
*These A.I. responses have been individually checked to ensure they match the accepted answer, but explanations may still be incorrect. Responses may give guidance but the A.I. might not be able to answer the question! This is particularly the case for questions based on diagrams, which the A.I. typically cannot interpret. Grade Gorilla uses Gemini, Deepseek and a range of other A.I. chatbots to generate the saved responses. Some answers have had human intervention for clarity or where the A.I. has not been able to answer the question.
Question 2:
The correct answer is:
C. 46
Reasoning: A foetus is a developing human before birth. Except for gametes (sperm and egg cells), all cells in the human body are diploid, meaning they contain 46 chromosomes (23 pairs). This includes cheek cells from a foetus. A foetus’s cheek cells are somatic cells, so they have the same number of chromosomes as an adult’s cheek cells — 46.
Question 3:
3. Correct Answer: A (K)
Reasoning: Meiosis is the specialized cell division that reduces the chromosome number by half to produce gametes (sperm and egg cells). In the diagram, arrow K shows the transition from adult parents to cells containing 23 chromosomes.
Question 4:
D. testis — ovary
Reasoning: Meiosis is the process that produces gametes (sex cells).
In males, meiosis occurs in the testes, producing sperm.
In females, meiosis occurs in the ovaries, producing eggs.
The other options list organs (penis, uterus) where meiosis does not occur.
Question 5:
5. Correct Answer: B (L)
Reasoning: Fertilization is the process where the sperm and egg fuse together. Arrow L shows these two individual gametes joining to form a single Zygote.
Question 6:
6. Correct Answer: D (M and N)
Reasoning: Mitosis is the process of cell division used for growth and repair, where daughter cells are identical to the parent cell. This occurs after a zygote is formed, allowing it to grow into a foetus (M) and continue growing into a young child (N).
Question 7:
C. XY
Reasoning: In humans, sex is determined by the combination of sex chromosomes:
XX = female
XY = male
YY is not possible in humans (lack of X is lethal).
XXX is usually a female with a chromosomal abnormality (Triple X syndrome).
Thus, the presence of a Y chromosome (as in XY) indicates a male.
Question 8:
Let's fill in the Punnett square correctly first.
We have:
Male gametes (sperm): X and Y
Female gametes (eggs): X and X
The Punnett square:
So:
i = XX → female genotype ✅, phenotype female ❌ → not "male"
ii = XY → male genotype ✅, phenotype male ✅
iii = XX → female genotype ✅, phenotype female ❌ → not "male"
iv = XY → male genotype ✅, phenotype male ✅
Now check given table options:
A. i — male, XX → wrong, XX is female ❌ B. ii — male, XY → correct ✅ C. iii — male, XX → wrong, XX is female ❌ D. iv — female, XY → wrong, XY is male ❌
Final answer: B. ii — male, XY ✅
Question 9:
C. 50%
Reasoning: The sex of a baby is determined by whether the sperm that fertilizes the egg carries an X or a Y chromosome.
The chance of a sperm carrying an X (resulting in a girl) is about 50%.
The chance of a sperm carrying a Y (resulting in a boy) is about 50%.
Previous children do not affect the probability of the next child’s sex — each pregnancy is an independent event.
So, even after having a boy, the chance the next baby is a boy remains 50%.
Question 10:
C. The children are identical twins
Reasoning:
A girl has XX chromosomes, a boy has XY.
If they were identical twins, they would have come from the same fertilized egg (zygote) and would share the same sex chromosomes (both XX or both XY).
Since one is a girl (XX) and the other is a boy (XY), they cannot be identical twins — they must be non-identical (fraternal) twins.
Therefore, statement C is not correct. ✅