Study Mendel's cross between two plants with a pair of contrasting characters. RRYY x rryy (Round Yellow x Wrinkled Green). He observed 4 types of combinations in F 2 , generation. Which of these were new combinations? Why do new features which are not present in the parents, appear in F 2 , generation?

In Mendel's classic experiments on inheritance, one of the key principles he discovered was the Law of Independent Assortment, which explains how genes for different traits segregate independently during gamete formation. To illustrate this principle, let's consider Mendel's cross between two plants with a pair of contrasting characters: Round Yellow ( RRYY ) and Wrinkled Green ( rryy ). Now, let's examine the combinations observed in the F 2 generation: Round Yellow (RRYY) . Round Green (RRyy) Wrinkled Yellow (rrYY) Wrinkled Green (rryy) The new combinations observed in the F 2 generation are "Round Green" ( RRyy ) and "Wrinkled Yellow" ( rrYY ). These combinations were not present in the parental generation and represent the result of the independent assortment of alleles during gamete formation. These new combinations arise due to Mendel's Laws of Independent Assortment and Segregation, which lead to genetic diversity in the offspring. Law of Independent Assortment: This principle states that alleles (gene variants) for different traits segregate independently during gamete formation. In this case, the alleles for seed shape (Round or Wrinkled) segregate independently of the alleles for seed colour (Yellow or Green). Each combination of seed shape and colour is equally likely in the offspring, leading to the appearance of new combinations not present in the parents.

Why are the traits acquired during the lifetime of an individual not inherited? Explain?

Traits acquired throughout an individual's life are not inherited, because acquired traits are affected by the environment in which the body lives. These traits are not coded into the body's DNA so, these traits cannot be inherited, these traits are used for the body to survive in a new environment. For example, the traits of a great scientist who received a Nobel Prize after his ongoing hard work in his study cannot be inherited in the next generation. These traits which can be inherited are colour of hair and eye, height, skin, etc.

What is the law of dominance of traits? Explain with an example.

Mendel proposed two general rules to consolidate his understanding of inheritance in monohybrid crosses. Today these rules are called the Principles or Laws of Inheritance: The first law or Law of Dominance and the second law or Law of Segregation. Law of Dominance: Characters are controlled by discrete units called factors. Factor occurs in pairs. In a dissimilar pair of factors pertaining to character one member of the pair dominates (dominant) the other (recessive). The law of dominance is used to explain the expression of only one of the parental characters in a monohybrid cross in the F 1 and the expression of both in the F 2 . It also explains the proportion of 3:1 obtained at the F 2 .

What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor? Justify your answer.

Homologous structures are the basic body structures of animals having similar structure but different function. Examples: Arm of human, wing of bat, and front leg of horse all of them have similar basic structures but entirely different functions. Yes, It is necessary that homologous structures always have a common ancestor. As explained in the above example, the basic structure of arm of human and wing of bat is similar but, they modified to perform different function in different vertebrates. Therefore, this shows that they have evolved from a common forefather.

‘‘The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it.’’ Justify this statement with the help of a flow chart showing sex-determination in human beings.

Humans contain 23 pairs of chromosomes, out of which 22 pairs are the autosomes and 1 pair is a sex chromosome. The females have two X chromosomes and males have one X and one Y chromosome. During the process of fertilization, the sperm carrying X chromosome fuses with the egg carrying X chromosome, then the baby will be female. If Y chromosome fuses with the egg carrying X chromosome then baby will be male. Therefore, the sex of a new born is a matter of chance and none of the parents may be considered responsible for it.

What are homologous structures? Give an example.

Homologous structures have a common basic structure, same origin and development but perform different functions. They develop from a common ancestor. Examples are forelimbs of reptiles, mammals and amphibians. Amphibians are cold-blood vertebrates. They survive on water and on land.

A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in F1 progeny?

Among the seven characteristics of pea plant taken by Mendel for his experiments. The violet colour of flower is dominant trait and white colour of flower is recessive trait. When pea plant bearing violet flower is bred with pea plant bearing white flowers the resulted progeny would consist of all violet flowers because violet is dominant. Violet flowers are represented by VV, whereas white flowers are represented by vv. The cross-breeding two plants results in having a F 1 character are Vv, Vv, Vv, Vv. Since V (i.e, violet colour) is dominant all flowers are violet.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 9 - Heredity and Evolution>CBSE-2023 (Delhi - I)>Q 16

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A cross between pea plant with white flowers (vv) and pea plant with violet flowers (VV) resulted in F₂ progeny in which ratio of violet (VV) and white (vv) flowers will be:

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Important Questions on Heredity and Evolution

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 9 - Heredity and Evolution>CBSE-2023 (Delhi - I)>Q 19

Study Mendel's cross between two plants with a pair of contrasting characters. RRYY x rryy (Round Yellow x Wrinkled Green). He observed 4 types of combinations in F₂, generation. Which of these were new combinations? Why do new features which are not present in the parents, appear in F₂, generation?

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 9 - Heredity and Evolution>CBSE-2023 (Delhi - II)>Q 20

Which pair of sex chromosome will determine a male?

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 9 - Heredity and Evolution>CBSE-2023 (Delhi - III)>Q 21

Which one of the given statements in incorrect:

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR SCIENCE>Chapter 9 - Heredity and Evolution>CBSE-2023 (Outside Delhi - I)>Q 22

In an experiment with pea plants, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plant to pure short plants in