CIE iGCSE Co-Ordinated Science B16.1 Chromosomes and genes Exam Style Questions Paper 2
▶️ Answer/Explanation
Sheep have 54 chromosomes in their body cells, which are diploid (2n). This means the diploid number is 54. Egg cells are gametes produced by meiosis, so they contain half the number of chromosomes (n), which is \(54 \div 2 = 27\). Gametes are haploid because they contain only one set of chromosomes. Therefore, egg cells contain 27 chromosomes and are haploid, which matches row A.
✅ Answer: (A)
✅ Answer: (A)
▶️ Answer/Explanation
In humans, sex is determined by the presence of the X and Y chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The Y chromosome carries the SRY gene which triggers the development of male characteristics. XO (Turner syndrome) results in a female, and YY is not viable.
✅ Answer: (B)
✅ Answer: (B)
▶️ Answer/Explanation
A diploid nucleus contains two full sets of chromosomes, while a haploid nucleus contains only one set.
So the diploid nucleus always has more chromosomes than the haploid nucleus from the same organism.
Haploid nuclei are produced by meiosis (not mitosis), so B and C are incorrect.
✅ Answer: (A)
So the diploid nucleus always has more chromosomes than the haploid nucleus from the same organism.
Haploid nuclei are produced by meiosis (not mitosis), so B and C are incorrect.
✅ Answer: (A)
▶️ Answer/Explanation
All eggs carry an \(X\) chromosome, while sperm may carry either \(X\) or \(Y\).
Fertilisation \(X_{egg} + Y_{sperm} \rightarrow XY \text{ (male)}\) and \(X_{egg} + X_{sperm} \rightarrow XX \text{ (female)}\); row B pairs these combinations correctly.
✅ Answer: (B)
Fertilisation \(X_{egg} + Y_{sperm} \rightarrow XY \text{ (male)}\) and \(X_{egg} + X_{sperm} \rightarrow XX \text{ (female)}\); row B pairs these combinations correctly.
✅ Answer: (B)
▶️ Answer/Explanation
Human gametes have 23 chromosomes. Chimpanzee gametes have one more, so 24 chromosomes. Gametes are haploid, so the diploid number is double, giving \(24 \times 2 = 48\) chromosomes.
✅ Answer: (D)
✅ Answer: (D)