Principles of Inheritance and Variation – Class 12 Biology (WBCHSE)
🧬 Principles of Inheritance and Variation – Class 12 Biology (WBCHSE)
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Introduction
Inheritance and variation are fundamental concepts in genetics that explain how traits are passed from parents to offspring. Gregor Mendel, the "Father of Genetics," laid the foundation of modern genetics through his experiments on pea plants. His principles help us understand how genetic traits are inherited and how variations arise.
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Mendel’s Laws of Inheritance
Mendel proposed three key laws based on his pea plant experiments:
1️⃣ Law of Dominance
✔ A dominant allele masks the expression of a recessive allele in a heterozygous condition.
✔ Example: In a cross between pure tall (TT) and dwarf (tt) pea plants, all F1 offspring are tall (Tt).
2️⃣ Law of Segregation
✔ Alleles separate during gamete formation, ensuring that each gamete carries only one allele for a trait.
✔ Example: A heterozygous (Tt) parent produces two types of gametes (T and t).
3️⃣ Law of Independent Assortment
✔ Genes for different traits assort independently during gamete formation.
✔ Example: In a dihybrid cross (RrYy × RrYy), the inheritance of seed color (Y/y) and seed shape (R/r) occurs independently.
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Types of Variation
✔ Heredity-based Variation – Inherited from parents (e.g., eye color, blood type).
✔ Environmental Variation – Caused by external factors (e.g., nutrition, climate).
✔ Mutational Variation – Arises from sudden genetic changes (e.g., albinism, Down syndrome).
Important Genetic Disorders
✔ Sickle Cell Anemia – Caused by a mutation in the hemoglobin gene.
✔ Hemophilia – A sex-linked disorder affecting blood clotting.
✔ Down Syndrome – Caused by trisomy of chromosome 21.
Most Important MCQs for West Bengal Higher Secondary Exam
Basic Concepts
1️⃣ Who is known as the "Father of Genetics"?
✅ a) Gregor Mendel
2️⃣ What is the unit of heredity?
✅ a) Gene
3️⃣ Mendel performed experiments on which plant?
✅ b) Pea plant (Pisum sativum)
4️⃣ Which law explains the separation of alleles during gamete formation?
✅ c) Law of Segregation
5️⃣ What is a dominant allele?
✅ b) An allele that expresses itself in heterozygous condition
Mendelian Inheritance
6️⃣ What is the phenotypic ratio in a monohybrid cross?
✅ c) 3:1
7️⃣ The genotypic ratio in a monohybrid cross is:
✅ b) 1:2:1
8️⃣ Which law states that traits assort independently?
✅ c) Law of Independent Assortment
9️⃣ A dihybrid cross results in which phenotypic ratio?
✅ d) 9:3:3:1
🔟 What is an example of incomplete dominance?
✅ b) Snapdragon flower color
Genetic Disorders
1️⃣1️⃣ Which disease is caused by the presence of an extra chromosome 21?
✅ c) Down Syndrome
1️⃣2️⃣ Hemophilia is a:
✅ a) Sex-linked disorder
1️⃣3️⃣ Sickle cell anemia occurs due to:
✅ b) Mutation in hemoglobin gene
1️⃣4️⃣ What is the reason for color blindness?
✅ c) Defective X-linked gene
1️⃣5️⃣ Turner syndrome occurs due to:
✅ a) Monosomy of X chromosome
Chromosomes and Mutation
1️⃣6️⃣ Humans have how many chromosomes?
✅ b) 46
1️⃣7️⃣ Which type of mutation leads to variation?
✅ c) Genetic mutation
1️⃣8️⃣ Who discovered the structure of DNA?
✅ b) Watson and Crick
1️⃣9️⃣ What is a karyotype?
✅ a) A complete set of chromosomes
2️⃣0️⃣ What is polyploidy?
✅ b) Presence of extra sets of chromosomes
DNA and Molecular Basis of Inheritance
2️⃣1️⃣ The sugar present in DNA is:
✅ a) Deoxyribose
2️⃣2️⃣ RNA differs from DNA because it contains:
✅ b) Uracil instead of Thymine
2️⃣3️⃣ What is the function of mRNA?
✅ c) Carries genetic code from DNA to ribosome
2️⃣4️⃣ Which enzyme is responsible for DNA replication?
✅ b) DNA Polymerase
2️⃣5️⃣ In RNA, the base complementary to Adenine is:
✅ c) Uracil
Application of Genetics
2️⃣6️⃣ Genetic engineering is widely used in:
✅ b) Biotechnology
2️⃣7️⃣ Which technique is used to identify genetic disorders before birth?
✅ c) Amniocentesis
2️⃣8️⃣ The Human Genome Project aimed to:
✅ a) Decode the complete genetic sequence of humans
2️⃣9️⃣ Which is an example of a genetically modified crop?
✅ b) Bt Cotton
3️⃣0️⃣ Gene therapy is used for treating:
✅ c) Genetic disorders
🔥 NEET-Oriented MCQs on Inheritance & Variation
Mendelian Genetics & Laws of Inheritance
3️⃣1️⃣ Which of the following is NOT a characteristic selected by Mendel in his pea plant experiments?
✅ c) Leaf shape
3️⃣2️⃣ If a heterozygous tall (Tt) pea plant is self-crossed, what is the expected percentage of short (tt) offspring?
✅ b) 25%
3️⃣3️⃣ In a test cross, a tall pea plant is crossed with a dwarf plant. If all offspring are tall, the genotype of the tall parent is:
✅ a) TT
3️⃣4️⃣ The physical appearance of an organism is called its:
✅ d) Phenotype
3️⃣5️⃣ If a pure red-flowered (RR) plant is crossed with a pure white-flowered (rr) plant, and the F1 generation has pink flowers, this is an example of:
✅ b) Incomplete dominance
Chromosomal Theory & Linkage
3️⃣6️⃣ Who proposed the Chromosomal Theory of Inheritance?
✅ a) Sutton and Boveri
3️⃣7️⃣ Which scientist discovered linkage in Drosophila?
✅ d) T.H. Morgan
3️⃣8️⃣ Genes located close together on the same chromosome and inherited together show:
✅ b) Linkage
3️⃣9️⃣ Crossing over occurs during which phase of meiosis?
✅ c) Prophase I
4️⃣0️⃣ If two genes have a recombination frequency of 50%, they are:
✅ d) Unlinked genes on different chromosomes
Sex Determination & Genetic Disorders
4️⃣1️⃣ In humans, the sex of a baby is determined by:
✅ b) The father’s gamete (X or Y chromosome)
4️⃣2️⃣ Which disorder is due to the absence of an X chromosome (XO)?
✅ a) Turner syndrome
4️⃣3️⃣ Which disorder is characterized by XXY chromosomes?
✅ c) Klinefelter syndrome
4️⃣4️⃣ What is the genetic basis of sickle cell anemia?
✅ c) A single base substitution in the β-globin gene
4️⃣5️⃣ In pedigree analysis, an affected male is represented by:
✅ b) A filled square
Molecular Genetics & Mutations
4️⃣6️⃣ Which type of mutation involves the addition or deletion of a single nucleotide, causing a frameshift?
✅ d) Frameshift mutation
4️⃣7️⃣ The process of RNA formation from DNA is called:
✅ a) Transcription
4️⃣8️⃣ A gene that can move from one chromosomal location to another is called a:
✅ c) Transposon
4️⃣9️⃣ Which enzyme is responsible for synthesizing RNA during transcription?
✅ b) RNA Polymerase
5️⃣0️⃣ Which type of bond joins two nucleotides in DNA?
✅ d) Phosphodiester bond
🔬 Conclusion
The principles of inheritance and variation form the foundation of genetics. Understanding Mendel’s laws, types of variation, and genetic disorders is crucial for exams like WBCHSE Higher Secondary. By mastering these concepts and practicing MCQs, students can excel in their biology exams!These NEET-oriented MCQs cover key concepts in genetics, inheritance, and molecular biology. Understanding these topics will help students tackle NEET 2025 questions effectively.
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