Case 1: Autosomal Recessive Disorder
A couple with normal appearance gives birth to a child suffering from a genetic disease.
Genetic analysis reveals both parents carry one defective allele, but the disease appears only in the child.
1. The inheritance pattern shown here is
A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive
✅ Answer: B
2. The parents are best described as
A. Diseased
B. Homozygous dominant
C. Carriers
D. Mutants
✅ Answer: C
3. Which disorder follows this inheritance pattern?
A. Haemophilia
B. Colour blindness
C. Sickle cell anaemia
D. Turner syndrome
✅ Answer: C
📘 Explanation: Autosomal recessive disorders appear only when both alleles are defective.
Case 2: Sex-Linked Disorder
In a family, a colour-blind father and a normal mother have children. None of the sons are colour-blind,
but all daughters are carriers.
4. Colour blindness is inherited as
A. Autosomal recessive
B. Autosomal dominant
C. X-linked recessive
D. Y-linked
✅ Answer: C
5. The daughters are carriers because
A. They inherit Y chromosome
B. They inherit one defective X chromosome
C. They inherit defective autosomes
D. Mutation occurs after birth
✅ Answer: B
6. The sons are normal because
A. They inherit normal X chromosome from mother
B. They inherit X chromosome from father
C. The gene is dominant
D. The gene is lethal
✅ Answer: A
Case 3: Enzyme Deficiency Disorder
A newborn shows abnormal mental development. Blood tests reveal accumulation of phenylalanine.
7. The disorder described is
A. PKU
B. Sickle cell anaemia
C. Down syndrome
D. Haemophilia
✅ Answer: A
8. The missing enzyme is
A. Tyrosinase
B. Amylase
C. Phenylalanine hydroxylase
D. Catalase
✅ Answer: C
9. This disorder mainly affects
A. Liver
B. Brain
C. Heart
D. Kidney
✅ Answer: B
Case 4: X-Linked Bleeding Disorder
10. The disorder is
A. PKU
B. Haemophilia
C. Thalassemia
D. Down syndrome
✅ Answer: B
11. Females are unaffected because
A. They do not inherit the gene
B. They are immune
C. One normal allele compensates
D. The gene is on Y chromosome
✅ Answer: C
12. This disorder is caused by deficiency of
A. Insulin
B. Clotting factors
C. Haemoglobin
D. Enzymes
✅ Answer: B
Case 5: Numerical Chromosomal Disorder
13. The disorder is
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Cri-du-chat syndrome
✅ Answer: C
14. The abnormality involved is
A. Monosomy
B. Trisomy
C. Polyploidy
D. Deletion
✅ Answer: B
15. The affected chromosome number is
A. 18
B. 21
C. X
D. Y
✅ Answer: B
Case 6: Monosomy of Sex Chromosome
16. The disorder is
A. Down syndrome
B. Turner syndrome
C. Klinefelter syndrome
D. PKU
✅ Answer: B
17. The chromosomal constitution is
A. XX
B. XO
C. XXY
D. XYY
✅ Answer: B
Case 7: Extra Sex Chromosome in Male
18. The disorder is
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Haemophilia
✅ Answer: B
19. This condition arises due to
A. Mutation
B. Crossing over
C. Nondisjunction
D. Deletion
✅ Answer: C
Case 8: Structural Chromosomal Abnormality
20. The disorder is
A. Down syndrome
B. Cri-du-chat syndrome
C. Turner syndrome
D. PKU
✅ Answer: B
21. The cause of this disorder is
A. Trisomy 21
B. Deletion of short arm of chromosome 5
C. Monosomy X
D. XXY condition
✅ Answer: B