Class 12 Biology (NCERT)

1. Gregor Mendel conducted his classical genetic experiments primarily on:

• A. Garden pea (Pisum sativum)
• B. Fruit fly (Drosophila)
• C. Maize
• D. Human pedigrees

2. Mendel's Law of Segregation states that:

• A. The two alleles of a gene separate from each other during gamete formation
• B. Genes located on different chromosomes assort independently
• C. All traits observed are always dominant
• D. Genetic traits always blend together in offspring

3. In a dihybrid cross between two heterozygous parents, the typical phenotypic ratio observed in the F2 generation is:

• A. 9:3:3:1
• B. 3:1
• C. 1:2:1
• D. 1:1:1:1

4. A cross between an F1 heterozygote and a homozygous recessive parent is specifically called a:

• A. Test cross
• B. Dihybrid cross
• C. Reciprocal cross
• D. Back cross to the dominant parent

5. Sex determination in humans is primarily based on the presence of:

• A. X and Y chromosomes
• B. Only autosomes
• C. Only X chromosomes
• D. Hormone levels alone

6. Haemophilia, a well-known bleeding disorder, is an example of a:

• A. Sex-linked recessive disorder
• B. Autosomal dominant disorder
• C. Autosomal recessive disorder
• D. Y-linked disorder

7. Down's syndrome in humans is primarily caused by:

• A. Trisomy of chromosome 21
• B. Deletion of chromosome 21
• C. Trisomy of the X chromosome
• D. Monosomy of chromosome 21

8. Pedigree analysis is a technique primarily used to study the:

• A. Inheritance pattern of a specific trait within a family
• B. DNA sequence of an organism
• C. Overall process of gamete formation
• D. Physical structure of a chromosome

9. Incomplete dominance results in a hybrid phenotype that is:

• A. Intermediate between the two parental phenotypes
• B. Identical to only one of the two parents
• C. A blend that eventually reverses over generations
• D. Never actually observed in nature

10. The ABO blood group system in humans is a classic example of:

• A. Multiple allelism
• B. Sex-linked inheritance
• C. Incomplete dominance exclusively
• D. Polygenic inheritance exclusively

11. Linked genes are genes that are located:

• A. On the same chromosome, and tend to be inherited together
• B. On entirely different chromosomes
• C. Only within mitochondrial DNA
• D. Only on the sex chromosomes

12. A mutation is best described as a:

• A. Sudden, heritable change occurring in the genetic material
• B. Non-heritable change limited to the phenotype only
• C. Change that can only result from crossing over
• D. A type of dominant trait exclusively