Heredity Class 10 Science Chapter 8 Important Question Answer – NCERT

Class 10th
Subject Science (NCERT)
Category Important Questions

Heredity Class 10 Science Chapter 8 Important Question Answer

Q1. How does the mechanism of hereditary work?

Ans – Cellular DNA is the information source for making proteins in the cell. A section of DNA that provides information for one protein is called the gene for that protein. Plant height can thus depend on the amount of a particular plant hormone. The amount of the plant hormone made will depend on the efficiency of the process for making it. Consider now an enzyme that is important for this process. If this enzyme works efficiently, a lot of hormone will be made, and the plant will be tall. If the gene for that enzyme has an alteration that makes the enzyme less efficient, the amount of hormone will be less, and the plant will be short. Thus, genes control  characteristics, or traits.

Q2. How do Mendel’s experiment show that traits are inherited independently? Most Important

Ans – In a dihybrid cross, Mendel observed that when two pairs of traits or characters were considered, each trait expressed independent of the other. Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F1 Generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F1 yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded, 3 short round seeded and 1 short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.

Q3. How do Mendel’s experiments show that traits may be dominant or recessive ?

Ans – Mendel studied several contrasting characters of pea plants. He found that reproduction by cross pollination of plants with alternative traits resulted in the first generation F1 displaying only one trait and no other trait. For example, when Mendel hybridized the tall pea plant and the short plant, he received all the plants tall in the first offspring generation F1. This meant that only one ancestral trait of the two traits showed. There was no mixed evidence of both of them. He grew F1 generation plants by self pollination. Not all plants in this second generation F2 were tall. A quarter of the plants were dwarfs. Mendel called the trait of tall plants dominant and the trait of dwarf plants recessive.

Q4. How is the sex of the child determined in human beings? Most Important

Ans – In human beings, sex is determined on the basis of specific sex chromosomes. Males have XY chromosomes and females have XX chromosomes. It is clear from this that the female does not have the Y chromosome. When offspring are produced by male-female combination, the female may not be able to produce a male infant at any stage because the male infant must have XY chromosomes.

In fertilization, if the X chromosome of a man is fused with the X chromosome of the woman, then it will form an XX pair. Hence, the child will be in the form of a girl.

But when a man’s Y chromosome combines with the female’s chromosome X, XY will be formed. This will lead to the birth of a boy.

Q5. What is meant by characteristics?

Ans – Characteristics, refer to the distinguishing qualities or features that define an individual, object, or phenomenon. Traits are specific enduring patterns, such as personality traits in psychology, that contribute to uniqueness. Characteristics set something apart and help identify or describe it, providing a basis for differentiation.

Q6. Gregor Mendel belonged to which country?

Ans – Czech Republic

Q7. Mendel crossed a tall pea plant (TT) and a short plant (tt) and produced progeny (Fi) from them. All plants were _________.

Ans – Tall (Tt)

Q8. As per Mendel’s Law, describe the independent assortment of two separate traits (rounded and green seeds) with ( wrinkled and yellow seeds) along with diagram.

Ans – Mendel’s Law of Independent Assortment states that the alleles for different traits segregate independently of each other during the formation of gametes. Let’s consider two traits: seed shape (rounded or wrinkled) and seed color (green or yellow).

In this case, let’s represent the dominant alleles for each trait with capital letters (R for round seeds, Y for yellow seeds) and the recessive alleles with lowercase letters (r for wrinkled seeds, y for green seeds).

If an individual has the genotype RrYy (heterozygous for both traits), the possible gametes produced during the process of independent assortment would be:

  1. RY
  2. Ry
  3. rY
  4. ry

These combinations result from the independent assortment of alleles for seed shape (R and r) and seed color (Y and y). Each gamete represents a unique combination of alleles.

Here’s a simplified diagram to illustrate the independent assortment:

This diagram shows the possible combinations of alleles for seed shape (R and r) along the horizontal axis and seed color (Y and y) along the vertical axis. The four squares represent the different combinations of alleles in the gametes due to the independent assortment of these traits.

Q9. Rounded seeds (dominant trait) were crossed with wrinkled seeds (recessive trait).
(i) What type of seeds will be produced in F1 generation ?
(ii) By self-pollination in F₁ seeds, what percentage of seeds will be rounded shape in F2 generation ?
Explain with diagram.

Ans – When rounded seeds (dominant trait, represented by the symbol R) are crossed with wrinkled seeds (recessive trait, represented by the symbol r), the F1 generation will be heterozygous for the trait, having the genotype Rr.

(i) F1 Generation: All the seeds in the F1 generation will have the rounded phenotype because the dominant trait (R) masks the expression of the recessive trait (r). Therefore, all seeds in the F1 generation will be rounded.

(ii) F2 Generation: When individuals from the F1 generation (Rr) are self-pollinated, the possible combinations of alleles in the F2 generation can be predicted as:

R r
r Rr rr

In this table, the possible genotypes are RR, Rr, Rr, and rr.

  • The phenotypes corresponding to these genotypes are:
    • RR and Rr: Rounded seeds
    • rr: Wrinkled seeds

So, in the F2 generation, the phenotypic ratio will be 3:1 for rounded seeds to wrinkled seeds.

If you’re looking for the percentage of rounded seeds in the F2 generation, you would consider the RR and Rr genotypes together. In this case, since both genotypes express the rounded phenotype, the percentage of rounded seeds would be 75% (3 out of 4) in the F2 generation.

Q10. Which sex chromosomes is present in females ?

Ans – XY

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