Class 12 Biology Important Chapter 5 Principles of Inheritances and Variation

Class 12 Biology Important Chapter 5 Principles of Inheritances and Variation Solutions English Medium As Per The New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters ASSEB Class 12 Biology Important Solutions in English and select need one. AHSEC Class 12 Biology Additional Notes Download PDF. HS 2nd Year Biology Additional Solutions.

Class 12 Biology Important Chapter 5 Principles of Inheritances and Variation

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Principles of Inheritances and Variation

Chapter: 5

IMPORTANT QUESTION AND ANSWER

Answer the Following Question:

1. Who is known as the father of genetics?

Ans: Gregor Johann Mendel.

2. What is the genotypic ratio in a monohybrid cross?

Ans: 1:2:1.

3. Name the scientist who proposed the chromosomal theory of inheritance.

Ans: Sutton and Boveri.

4. Which disorder is caused due to trisomy of chromosome 21?

Ans: Down’s syndrome.

5. Which genetic disorder is caused by a point mutation in the β-globin gene?

Ans: Sickle cell anaemia.

6. What is a test cross?

Ans: A cross between an individual of dominant phenotype and a homozygous recessive individual.

7. What are multiple alleles? Give an example.

Ans: Multiple alleles are more than two alternative forms of a gene that can occupy the same locus.

Example: ABO blood group in humans is determined by three alleles – IA, IB, and i.
Only two alleles exist in any individual, but more than two alleles occur in the population.

8. Define and explain the Law of Independent Assortment with an example.

Ans: According to this law, “When two or more characters are inherited together, alleles of different gene pairs assort independently during gamete formation.”

Example: In a dihybrid cross between RrYy and RrYy, four combinations appear in 9:3:3:1 phenotypic ratio.

9. Explain the chromosomal theory of inheritance.

Ans: (i) Proposed by Sutton and Boveri.

(ii) It states that genes are located on chromosomes and they segregate and assort independently during meiosis.

(iii) The behavior of chromosomes during gamete formation correlates with Mendelian laws.

10. Describe polygenic inheritance with a suitable example.

Ans: (i) Polygenic inheritance is the inheritance of traits controlled by multiple genes.

(ii) Each gene has an additive effect.

Example: Skin colour in humans is controlled by three genes A, B, and C. The more dominant alleles, the darker the skin.

11. What is pleiotropy? Give an example.

Ans: Pleiotropy is a condition where one gene affects multiple traits.

Example: In phenylketonuria, a single gene mutation affects mental development and skin pigmentation.

12. Describe the genetic basis and symptoms of sickle cell anaemia.

Ans: (i) Caused by point mutation in β-globin gene.

(ii) Glutamic acid (GAG) is replaced by valine (GUG).

(iii) HbSHbS genotype causes RBCs to become sickle-shaped under low oxygen.

(iv) Symptoms include anaemia, fatigue, and pain.

13. Describe Down’s Syndrome with its cause and symptoms.

Ans: (i) Caused by trisomy of chromosome 21 (i.e., 47 chromosomes).

(ii) Symptoms: mental retardation, broad palm crease, short stature, flattened face, open mouth, heart defects.

(iii) It is a chromosomal disorder.

14. What do you mean by true breeding lines?

Ans: True breeding lines are those that consistently produce offspring with the same trait when self-pollinated over generations. They are homozygous for the trait in question.

15. What is linkage? How does it affect inheritance?

Ans: Linkage is the physical association of genes on the same chromosome. Linked genes are usually inherited together and do not assort independently, altering Mendel’s expected ratios.