Part 6: Mendelian Disorders in Humans (25 MCQs)
Part 6: Mendelian Disorders in Humans (25 MCQs)
Q126. Mendelian disorders are caused due to:
a) Mutations in multiple genes
b) Mutations in a single gene
c) Chromosome number changes
d) Environmental factors
Answer: b
- b) Correct: Mendelian disorders = monogenic (single-gene) disorders.
- a) Polygenic disorders involve multiple genes.
- c) Chromosomal disorders, not Mendelian.
- d) Environmental disorders (e.g., deficiency diseases).
Q127. Which of the following is a Mendelian disorder?
a) Down’s syndrome
b) Klinefelter’s syndrome
c) Thalassemia
d) Turner’s syndrome
Answer: c
- c) Correct: Thalassemia = single-gene disorder.
- a, b, d) Chromosomal disorders.
Q128. Which of the following is NOT a Mendelian disorder?
a) Sickle-cell anemia
b) Cystic fibrosis
c) Hemophilia
d) Down’s syndrome
Answer: d
- d) Correct: Down’s = chromosomal disorder (trisomy 21).
Q129. Sickle-cell anemia is caused due to:
a) Defect in chromosome number
b) Point mutation in β-globin gene
c) Deletion of X chromosome
d) Duplication of autosome
Answer: b
- b) Correct: Single point mutation in β-globin gene (GAG → GTG) → glutamic acid replaced by valine.
Q130. Sickle-cell anemia is inherited as:
a) Autosomal dominant
b) Autosomal recessive
c) X-linked recessive
d) Y-linked
Answer: b
- b) Correct: It is autosomal recessive.
Q131. In sickle-cell anemia, heterozygotes (AS) are:
a) Completely normal
b) Completely diseased
c) Carriers with both normal and sickle cells
d) Dead at birth
Answer: c
- c) Correct: Heterozygotes = carriers with both normal and sickle RBCs.
Q132. Heterozygous sickle-cell individuals show resistance to:
a) Malaria
b) Tuberculosis
c) Influenza
d) Typhoid
Answer: a
- a) Correct: Carriers resist malaria (Plasmodium falciparum) infection.
Q133. Thalassemia affects the synthesis of:
a) Insulin
b) Hemoglobin chains
c) Enzymes in glycolysis
d) Hormones
Answer: b
- b) Correct: Thalassemia = defect in hemoglobin chain synthesis (α or β).
Q134. β-thalassemia is caused due to defect in:
a) α-chain of hemoglobin
b) β-chain of hemoglobin
c) γ-chain of hemoglobin
d) δ-chain of hemoglobin
Answer: b
- b) Correct: β-thalassemia = defective or reduced β-chain synthesis.
Q135. Which of the following is a symptom of severe thalassemia?
a) Enlargement of spleen and liver
b) Formation of tumors
c) Nerve degeneration
d) Increased resistance to malaria
Answer: a
- a) Correct: Severe thalassemia = splenomegaly, anemia, bone deformities.
Q136. Thalassemia is inherited as:
a) Autosomal dominant
b) Autosomal recessive
c) X-linked recessive
d) Y-linked
Answer: b
- b) Correct: Thalassemia = autosomal recessive.
Q137. Which of the following is an example of pleiotropy?
a) Hemophilia
b) Sickle-cell anemia
c) Thalassemia
d) Color blindness
Answer: b
- b) Correct: Sickle-cell anemia = pleiotropy (single gene affects RBC shape, O₂ transport, malaria resistance).
Q138. The first human disease shown to be due to a mutation in a single gene was:
a) Cystic fibrosis
b) Sickle-cell anemia
c) Thalassemia
d) Hemophilia
Answer: b
- b) Correct: Sickle-cell anemia was first linked to a specific genetic mutation.
Q139. Cystic fibrosis is caused by mutation in gene coding for:
a) β-globin
b) Chloride channel protein (CFTR)
c) Insulin
d) Collagen
Answer: b
- b) Correct: Cystic fibrosis → mutation in CFTR gene (chloride transport defect).
Q140. Which of the following is an autosomal recessive disorder?
a) Hemophilia
b) Sickle-cell anemia
c) Color blindness
d) Duchenne muscular dystrophy
Answer: b
- b) Correct: Sickle-cell anemia = autosomal recessive.
Q141. Which Mendelian disorder is most common among Mediterranean populations?
a) Hemophilia
b) Thalassemia
c) Color blindness
d) Cystic fibrosis
Answer: b
- b) Correct: Thalassemia prevalence is high in Mediterranean regions.
Q142. A child of carrier parents for thalassemia has probability of being affected:
a) 0%
b) 25%
c) 50%
d) 100%
Answer: b
- b) Correct: Carrier × Carrier (Tt × Tt) → 25% affected (tt).
Q143. Which of the following is INCORRECT for sickle-cell anemia?
a) It is caused by a point mutation
b) Homozygotes show severe anemia
c) Heterozygotes are completely normal
d) Provides resistance to malaria
Answer: c
- c) Correct: Heterozygotes are carriers, not completely normal.
Q144. Albinism is caused due to:
a) Defect in tyrosinase enzyme synthesis
b) Defect in hemoglobin synthesis
c) Extra copy of chromosome 21
d) Mutation in CFTR gene
Answer: a
- a) Correct: Albinism = defect in tyrosinase enzyme → no melanin production.
Q145. Which of the following is NOT inherited in a Mendelian fashion?
a) Hemophilia
b) Thalassemia
c) Down’s syndrome
d) Sickle-cell anemia
Answer: c
- c) Correct: Down’s = chromosomal (trisomy 21), not Mendelian.
Q146. Phenylketonuria (PKU) is caused due to:
a) Deficiency of tyrosinase
b) Deficiency of phenylalanine hydroxylase
c) Deficiency of hemoglobin
d) Deficiency of insulin
Answer: b
- b) Correct: PKU = deficiency of phenylalanine hydroxylase → accumulation of phenylalanine.
Q147. Which of the following is NOT a symptom of PKU?
a) Mental retardation
b) Accumulation of phenylalanine
c) Excess melanin production
d) Seizures
Answer: c
- c) Correct: PKU → reduced melanin, not excess.
Q148. Which test is used to detect genetic disorders in unborn child?
a) ECG
b) Amniocentesis
c) X-ray
d) Dialysis
Answer: b
- b) Correct: Amniocentesis analyzes fetal cells for genetic abnormalities.
Q149. Which type of mutation causes sickle-cell anemia?
a) Deletion
b) Substitution
c) Insertion
d) Frame-shift
Answer: b
- b) Correct: Point substitution mutation (GAG → GTG).
Q150. In thalassemia, defective hemoglobin leads to:
a) Excess oxygen transport
b) Reduced oxygen transport
c) Normal RBC function
d) Increased ATP production
Answer: b
- b) Correct: Defective hemoglobin = reduced oxygen-carrying capacity.
Class 12 Biology MCQs, Inheritance and Variation notes, NEET UG genetics questions, Mendelian inheritance Class 12, Chromosomal disorders MCQs, Linkage and crossing over, CBSE Biology exam prep, NCERT Class 12 solutions, principles of inheritance class 12 MCQs, inheritance and variation NEET solved questions, CBSE biology chapter 4 question bank, class 12 genetics NEET preparation, NCERT based inheritance notes pdf, chromosomal disorders class 12 MCQs, mendelian inheritance multiple choice questions, online learning biology NEET