NCERT Class 10 Science Chapter 9 Notes Heredity And Evolution- Download PDF Notes

NCERT Class 10 Science Chapter 8 Notes: Heredity refers to the phenomenon by which parental traits are passed on to offspring. Heredity is a powerful determinant of one's features, like eye color, height, and inherited disorders. The branch of science dealing with heredity and variation came to be termed genetics. Gregor Mendel, its founder, started experimenting on peas and came to establish how attributes are passed along generations.

This Story also Contains

1. Mendelian Inheritance
2. Sex Determination in Humans
3. Important Topics of Class 10 Science Chapter 8: Heredity
4. Most Important Questions of Class 10 Biology Chapter 8
5. Approach to solve questions of Class 10 Biology Chapter 8 Heredity
6. Chapter-Wise NCERT Class 10 Notes Science

Understanding heredity is essential as it explains why individuals of the same species show similarities and differences. This chapter in NCERT Notes for Class 10 Science explores the fundamental principles of inheritance, Mendel’s laws, sex determination, and the impact of variations on evolution. By grasping these concepts, students can better understand how genetic traits are inherited and how they contribute to species diversity. This chapter is important for CBSE students who are giving exams and NCERT Solutions provide step-by-step solutions to help solidify these concepts.

Mendelian Inheritance

Gregor Mendel performed experiments on pea plants (Pisum sativum) and established the basic laws of heredity. Through his experiments, he discovered the three fundamental laws of inheritance.

Mendel's Laws of Inheritance

Law of Dominance: In a hybrid between two differing traits, the trait expressed in the first generation (F₁) is dominant, and the unexpressed trait is recessive.

Law of Segregation: The alleles for a characteristic separate when forming gametes such that each gamete has just one allele.

Law of Independent Assortment: Genes of different traits sort out independently of one another at gamete formation, resulting in varied combinations of traits in the offspring.

Monohybrid and Dihybrid Cross

Monohybrid Cross: A cross of a single gene for one trait (e.g., tall and dwarf plants). The F₂ generation has a 3:1 ratio of dominant to recessive traits.

Dihybrid Cross: A cross between two characteristics (e.g., seed shape and seed color). The F₂ generation has a 9:3:3:1 phenotypic ratio.

Inheritance of Traits

Traits are inherited due to genes, which come in pairs known as alleles. Such traits may be:

Dominant: Always expressed even when in one copy (e.g., tallness in pea plants).

Recessive: Only expressed when two copies are present (e.g., dwarfness in pea plants).

Variation and Evolution

Variations occur because of genetic recombination, mutation, and the environment. Variations are crucial for evolution as they enable species to evolve in response to environmental changes over generations.

Sex Determination in Humans

Sex in an offspring is determined by the sex chromosomes (X and Y):

Females (XX): Always inherit an X chromosome.

Males (XY): Can inherit either an X or Y chromosome.

If a sperm with an X chromosome fertilizes an egg, a female (XX) is born. If a sperm with a Y chromosome fertilizes an egg, a male (XY) is born.

So, the father decides the sex of the child.

Acquired vs. Inherited Traits

Acquired Traits: Traits acquired during the lifetime of an individual as a result of environmental factors (e.g., bodybuilding, scars). These are not inherited.

Inherited Characteristics: Characteristics inherited by offspring from parents through genes (e.g., hair color, texture of hair).

Also , read Subject-Wise NCERT Solutions

NCERT Solutions for Class 10 Maths

NCERT Solutions for Class 10 Science

Important Topics of Class 10 Science Chapter 8: Heredity

The key topics from this chapter are listed below for simple and quick revision:

• Heredity and Its Importance

• Mendel’s Laws of Inheritance

• Monohybrid and Dihybrid Cross

• Sex Determination in Humans

• Inherited Traits and Variations

Subject Wise NCERT Exemplar Solutions

NCERT Exemplar Class 10 Maths solutions

NCERT Exemplar Class 10 Science solutions

Most Important Questions of Class 10 Biology Chapter 8

This chapter explains how characters are passed from parents to offspring. It covers Mendel’s Laws of Inheritance and the difference between dominant and recessive traits. Students will also learn about genetic crosses and how different traits are inherited. Some of the most important questions from Heredity are given below to help you prepare better for exams.

Question 1: Males have a pair of chromosomes in which

A. Both are normal-sized X

B. One is a normal-sized Y, and the other is a short one called X

C. The Y chromosome is absent

D. one in normal-sized X and the other is a short one called Y

Answer:
Males have a mismatched pair of chromosomes in which one is a normal-sized X and the other is a short one called Y.

Hence, the correct option is (d), one in normal-sized X and the other is a short one called Y

Question 2: A pink-flowered Snapdragon plant was crossed with a red-flowered Snapdragon plant. What type of phenotype/s is/are expected in the progeny?

Answer:

Pink color flowers in snapdragons have genotype Rr
Red flowered snapdragons have genotype RR when they are both crossed

	R	R
R	RR	RR
r	Rr	Rr

Phenotype-

Red: Pink: White

2 : 2 : 0

So the progeny that we get are red and pink flowered plants only.

Question 3: Which law/s is/are explained on the basis of the Monohybrid cross?

Answer:

The Law of Dominance and the Law of Segregation are explained through Mendel's monohybrid cross. The Law of Dominance states that when two pure-breeding plants with different traits are crossed, one trait (dominant) masks the expression of the other (recessive). The Law of Segregation explains that during gamete formation, the two alleles for a trait separate, so each gamete carries only one allele.

Question 4: What will be the result if a child inherits the X chromosome from their father?

Answer:

All the children will inherit an X-chromosome from their mother regardless of whether they are boys or girls and thus, the sex of the children will be determined by what they inherit from their father. Therefore, if a child who inherits the X chromosome from their father will be a girl (XX).

Question 5: A Tall plant with Red seeds (both dominant traits) was crossed with a dwarf plant with white seeds. If the segregating progeny produced an equal number of tall red and dwarf white plants, what would be the genotype of the parents?

Answer:

To determine the genotypes of the parents, let's assign symbols to represent the alleles for the traits:

T = Tall (dominant)

t = Dwarf (recessive)

R = Red seeds (dominant)

r = White seeds (recessive)

The genotype of the tall plant with red seeds (dominant traits) can be represented as TtRr, indicating that it carries one dominant allele for tallness (T) and one recessive allele for dwarfness (t), as well as one dominant allele for red seeds (R) and one recessive allele for white seeds (r).

The genotype of the dwarf plant with white seeds (both recessive traits) can be represented as ttrr, indicating that it carries two recessive alleles for both dwarfness (t) and white seeds (r).

Therefore, the genotypes of the parents are TtRr and ttrr.

Also, Students can refer to:

NCERT Solutions for Class 10 Science Chapter 8 Heredity.

NCERT Exemplar Class 10 Science Chapter 8 Solutions Heredity

Approach to solve questions of Class 10 Biology Chapter 8 Heredity

To tackle the questions from this chapter, students should focus on the basic concepts of heredity, such as Mendel's experiments, dominant and recessive traits, and Punnett squares. A little more attention should be given to monohybrid and dihybrid crosses, ratios, and how characters are inherited, as these topics often come in exams. Short notes can be prepared on Mendel's Laws, along with their examples. Students should also practice the regular use of Punnett squares, and how sex is determined in humans is also an essential topic from an exam point of view. Try to solve the previous years' papers, and also other extra questions, to get familiar with the question pattern, which helps in performing better in the upcoming board examination.

Chapter-Wise NCERT Class 10 Notes Science

Given below are the chapter-wise links of class 10 notes: