Class 12 Anthropology Important Chapter 2 Genetics

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Class 12 Anthropology Important Chapter 2 Genetics

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Genetics

Chapter: 2

IMPORTANT QUESTION AND ANSWER

Answer the Following Questions:

1. Define allele.

Ans: Alleles are alternative forms of a gene that occupy the same position (locus) on homologous chromosomes. 

For example, the gene for plant height has two alleles: 

‘T’ for tallness and ‘t’ for dwarfness.

2. What is a Punnett square?

Ans: A Punnett square is a diagrammatic tool used in genetics to predict the genotype and phenotype of offspring resulting from a particular cross or breeding experiment.

3. State the Law of Dominance.

Ans: According to Mendel’s Law of Dominance, in a pair of contrasting traits, one trait (dominant) expresses itself in the hybrid (F₁ generation), while the other (recessive) remains hidden.

4. Give one example of codominance in humans.

Ans: In the MN blood group system, both M and N alleles are codominant. So, individuals with genotype MN express both M and N antigens on their red blood cells.

5. What is a genotype?

Ans: Genotype refers to the genetic constitution or the set of genes carried by an organism. For example, TT, Tt, and tt are genotypes for the trait of plant height.

6. What is the importance of Mendel’s work in genetics?

Ans: Mendel’s work laid the foundation of modern genetics. His experiments with pea plants established the basic laws of heredity—Law of Segregation and Law of Independent Assortment—explaining how traits are inherited.

7. What is meant by purity of gametes?

Ans: Purity of gametes means that during gamete formation, each gamete receives only one allele of a gene pair, ensuring that traits are passed down in a pure form without blending.

8. Mention two types of chromosomal aberrations.

Ans: (i) Numerical aberration – changes in the number of chromosomes (e.g., trisomy 21).

(ii) Structural aberration – changes in chromosome structure (e.g., deletion, translocation).

9. Explain Mendel’s Law of Segregation.

Ans: Mendel’s Law of Segregation states that during the formation of gametes, the two alleles for each trait separate (segregate) so that each gamete receives only one allele. This means traits do not blend; instead, they retain their distinct identity and reappear in the next generation. This was evident in Mendel’s monohybrid cross, where the recessive trait reappeared in the F₂ generation in a 3:1 phenotypic ratio.

10. Describe the significance of Mendel’s Dihybrid Cross.

Ans: Mendel’s dihybrid cross involved two traits: seed shape (round/wrinkled) and plant height (tall/dwarf). The F₂ generation showed a 9:3:3:1 phenotypic ratio, which demonstrated that the inheritance of one trait is independent of another. This formed the basis for Mendel’s Law of Independent Assortment, which showed that genes located on different chromosomes assort independently during gamete formation.

11. What is Down’s Syndrome? Mention its cause and symptoms.

Ans: Down’s Syndrome is a chromosomal disorder caused by trisomy of chromosome 21 (presence of an extra copy). It results from nondisjunction during meiosis.

Symptoms include: short stature, broad hands, flattened facial features, mental retardation, and a cheerful personality. Affected individuals have 47 chromosomes instead of the normal 46.

12. Write a short note on Klinefelter’s Syndrome.

Ans: Klinefelter’s Syndrome occurs in males who have an extra X chromosome (XXY), making their total chromosome number 47.

Characteristics include: small testes, lack of sperm production (infertility), breast development (gynecomastia), sparse body hair, and tall stature. It is a sex chromosome-related disorder.