DNA & RNA
1. The hereditary material in most living organisms is:
(A) Protein
(B) DNA
(C) Lipid
(D) Carbohydrate
Answer: (B) DNA
Explanation: DNA stores and transmits genetic information in most organisms.
2. The basic unit of DNA is called:
(A) Amino acid
(B) Nucleotide
(C) Chromosome
(D) Gene
Answer: (B) Nucleotide
3. Which nitrogenous base is present in DNA but not in RNA?
(A) Adenine
(B) Guanine
(C) Thymine
(D) Cytosine
Answer: (C) Thymine
Explanation: DNA contains thymine, whereas RNA contains uracil in its place.
4. Which nitrogenous base is found in RNA instead of thymine?
(A) Adenine
(B) Uracil
(C) Guanine
(D) Cytosine
Answer: (B) Uracil
5. Which molecule generally carries genetic instructions from DNA to ribosomes for protein synthesis?
(A) mRNA
(B) ATP
(C) Lipid
(D) Glucose
Answer: (A) mRNA
Genes & Chromosomes
6. A gene is best described as:
(A) A type of cell
(B) A unit of heredity containing information for a functional product or trait
(C) A type of protein
(D) A complete organism
Answer: (B) A unit of heredity containing information for a functional product or trait
7. Genes are located on:
(A) Ribosomes
(B) Chromosomes
(C) Cell membranes
(D) Lysosomes
Answer: (B) Chromosomes
8. How many pairs of chromosomes are normally present in a human somatic cell?
(A) 22
(B) 23
(C) 44
(D) 46
Answer: (B) 23
Explanation: Humans normally have 46 chromosomes arranged in 23 pairs.
9. Human gametes normally contain:
(A) 46 chromosomes
(B) 44 chromosomes
(C) 23 chromosomes
(D) 22 pairs of chromosomes
Answer: (C) 23 chromosomes
Mendel’s Laws & Inheritance
10. Gregor Mendel conducted his famous experiments mainly using:
(A) Maize
(B) Pea plants
(C) Wheat
(D) Rice
Answer: (B) Pea plants
11. Mendel is known as the:
(A) Father of Genetics
(B) Father of Evolution
(C) Father of Cytology
(D) Father of Microbiology
Answer: (A) Father of Genetics
12. Mendel’s law of segregation states that:
(A) Alleles separate during gamete formation
(B) All traits are dominant
(C) Genes are destroyed during reproduction
(D) Chromosomes never separate
Answer: (A) Alleles separate during gamete formation
13. The law of independent assortment states that:
(A) All genes are inherited together
(B) Alleles of different genes can assort independently during gamete formation, when the genes are independently assorting
(C) Dominant traits disappear
(D) Recessive traits cannot be inherited
Answer: (B) Alleles of different genes can assort independently during gamete formation, when the genes are independently assorting
14. An organism having two identical alleles for a particular gene is called:
(A) Heterozygous
(B) Homozygous
(C) Hybrid
(D) Hemizygous
Answer: (B) Homozygous
15. An organism having two different alleles for a particular gene is called:
(A) Homozygous
(B) Heterozygous
(C) Haploid
(D) Purebred
Answer: (B) Heterozygous
Dominant & Recessive Traits
16. A dominant allele is one that:
(A) Is always more common in a population
(B) Can determine the phenotype when present in a heterozygote
(C) Is always beneficial
(D) Is found only in males
Answer: (B) Can determine the phenotype when present in a heterozygote
17. A recessive trait is generally expressed when:
(A) At least one dominant allele is present
(B) Two recessive alleles are present in a diploid organism
(C) The organism is always male
(D) The gene is located in mitochondria
Answer: (B) Two recessive alleles are present in a diploid organism
18. In the cross Tt × Tt, where T is dominant, the expected phenotypic ratio is:
(A) 1:1
(B) 2:1
(C) 3:1
(D) 1:2:1
Answer: (C) 3:1
19. In the cross Tt × Tt, the expected genotypic ratio is:
(A) 3:1
(B) 1:1
(C) 1:2:1
(D) 2:1
Answer: (C) 1:2:1
Blood Groups
20. The ABO blood group system is determined primarily by:
(A) Antigens on red blood cells and corresponding antibodies in plasma
(B) The number of white blood cells
(C) Haemoglobin concentration only
(D) Platelet count
Answer: (A) Antigens on red blood cells and corresponding antibodies in plasma
21. A person with blood group A normally has:
(A) A antigen and anti-B antibody
(B) B antigen and anti-A antibody
(C) Both A and B antigens
(D) Neither A nor B antigen
Answer: (A) A antigen and anti-B antibody
22. A person with blood group AB normally has:
(A) Anti-A antibodies only
(B) Anti-B antibodies only
(C) Both anti-A and anti-B antibodies
(D) Neither anti-A nor anti-B antibodies
Answer: (D) Neither anti-A nor anti-B antibodies
23. In the ABO system, a person with blood group O normally has:
(A) A and B antigens
(B) A antigen only
(C) B antigen only
(D) Neither A nor B antigen
Answer: (D) Neither A nor B antigen
24. Which blood group is traditionally known as the universal red-cell donor in the ABO/Rh system?
(A) AB positive
(B) O negative
(C) A positive
(D) B negative
Answer: (B) O negative
Explanation: O-negative red cells lack A, B and RhD antigens and are commonly used for emergency red-cell transfusion when the recipient’s type is unknown, subject to clinical protocols.
Sex Determination
25. In humans, the sex of a child is determined by:
(A) The mother’s ovum only
(B) The father’s sperm chromosome
(C) The mother’s blood group
(D) The child’s nutrition
Answer: (B) The father’s sperm chromosome
Explanation: The ovum normally contributes an X chromosome, while sperm carries either X or Y. XX is typically female and XY typically male.
26. A human male normally has which pair of sex chromosomes?
(A) XX
(B) XY
(C) YY
(D) XO
Answer: (B) XY
27. A human female normally has which pair of sex chromosomes?
(A) XY
(B) YY
(C) XX
(D) XO
Answer: (C) XX
Genetic Disorders
28. Down syndrome is usually caused by:
(A) Trisomy of chromosome 21
(B) Monosomy of chromosome 21
(C) Mutation in the insulin gene
(D) Absence of the X chromosome
Answer: (A) Trisomy of chromosome 21
29. Haemophilia is commonly inherited as:
(A) X-linked recessive disorder
(B) Y-linked dominant disorder
(C) Autosomal dominant disorder
(D) Mitochondrial disorder
Answer: (A) X-linked recessive disorder
30. Sickle-cell disease is associated with an abnormal form of:
(A) Haemoglobin
(B) Insulin
(C) Collagen
(D) Keratin
Answer: (A) Haemoglobin
Must-Memorize Genetics Associations
| Topic | Key Fact |
|---|---|
| DNA | Main hereditary material in most organisms |
| RNA | Usually single-stranded; contains uracil |
| DNA base | Thymine |
| RNA base | Uracil |
| Basic unit of DNA | Nucleotide |
| Gene | Unit of heredity |
| Genes | Located on chromosomes |
| Human chromosomes | 46 (23 pairs) |
| Human gametes | 23 chromosomes |
| Mendel | Father of Genetics |
| Mendel’s organism | Pea plant |
| Segregation | Alleles separate during gamete formation |
| Independent assortment | Alleles of different genes can assort independently |
| Homozygous | Same alleles |
| Heterozygous | Different alleles |
| Dominant allele | Expressed in heterozygote under complete dominance |
| Recessive trait | Usually expressed when two recessive alleles are present |
| ABO blood group | Based on A/B antigens and antibodies |
| O negative | Common universal red-cell donor type |
| AB positive | Common universal red-cell recipient type for red cells |
| Female | XX |
| Male | XY |
| Down syndrome | Trisomy 21 |
| Haemophilia | X-linked recessive |
| Sickle-cell disease | Abnormal haemoglobin |
⭐ Very High-Yield Application Questions
Child’s sex → Determined by X- or Y-bearing sperm
DNA → Genetic information storage
mRNA → Carries coding information for protein synthesis
Gene → Unit of heredity
Chromosome → Carries genes
Tt × Tt → 3:1 phenotype ratio
Tt × Tt → 1:2:1 genotype ratio
Two identical alleles → Homozygous
Two different alleles → Heterozygous
Trisomy 21 → Down syndrome
X-linked recessive → Haemophilia