CBSE Class 10 Science Notes Chapter 9 Heredity and Evolution

CBSE Class 10 Science Notes Chapter 9 Heredity and Evolution:- Chapter 9 of CBSE Class 10 Science is all about heredity and evolution. Heredity is the process by which traits or characteristics are passed from parents to their children. It helps explain why children often look like their parents. Evolution is the process by which living things change over time, guiding to the variety of species we see today. The heredity class 10 notes explain concepts like how genes work and the inheritance patterns seen in plants and animals. 

The heredity and evolution class 10 notes provide easy-to-understand information about how traits are inherited and how species evolve through natural processes. This chapter is important for understanding how life has developed and changed over time, and using these heredity and evolution class 10 notes will help you grasp these concepts better.

Check out: CBSE Class 10th Books

CBSE Class 10 Science Chapter 9 Heredity and Evolution Overview

Chapter 9 of CBSE Class 10 Science explores the important concepts of heredity and evolution. Check out the CBSE Class 10 Science Chapter 9 Heredity and Evolution Overview here:- 

1. The chapter discusses Gregor Mendel’s experiments with pea plants, which formed the foundation of our understanding of inheritance patterns and how traits are passed from one generation to the next.

2. It explains the role of genes in heredity, highlighting how genes, located on chromosomes, carry the genetic information that determines traits like eye colour and height and are passed from parents to offspring.

3. The chapter also covers how variation occurs in offspring, which results from genetic recombination, mutations, and environmental factors, guiding to diversity within a species that aids in survival and adaptation.

4. It introduces the theory of evolution, explaining how species evolve over time through natural selection, where organisms best suited to their environment survive and reproduce, passing on beneficial traits to the next generation.

5. Finally, the chapter discusses the evolution of humans, tracing the key stages from early hominids to modern humans, and explaining how humans have evolved physically and behaviorally over millions of years.

Check out: CBSE Class 10th Sample Papers

CBSE Class 10 Science Notes Chapter 9 Heredity and Evolution

Heredity

Hereditary features are passed down from one generation to the next. The functional components of heredity that pass traits from parents to children are called genes. Genes are little segments of DNA that code for particular RNA or proteins.

The area of biology known as genetics studies genes, inheritance, and variations.

Sexual Reproduction

A man and a female are the two persons involved in the reproductive mode.
They generate gametes, or sex cells, which combine to create a new organism.

Genes

The functional unit of heredity is the gene. In living things, each gene regulates one or more specific defining traits.

Mendel’s Work

The “Father of Genetics,” Gregor Johann Mendel, was an Austrian monk who studied pea plants to comprehend the idea of heredity.
The field of contemporary genetics was founded by his research.
The Law of Dominance, the Law of Segregation, and the Law of Independent Assortment are the three fundamental laws of inheritance that he created.

Dominant Traits

Dominant qualities are those that manifest themselves in an organism in all conceivable configurations and are visible.

We may observe from Mendel’s experiment that in pea plants, the tall trait tends to express more than the short phenotype.
As a result, the taller feature of the plant is considered to be more prominent than the shorter one.

Recessive Traits

Recessive traits are those that do not manifest when a dominant allele is present.

Therefore, when a dominant allele is present, a recessive trait or characteristic is present in the organism but is not visible.

Monohybrid Cross

A monohybrid cross is one in which two organisms are crossed while just one character is taken into account.
The monohybrid ratio is the proportion of characteristics that result from this cross at the F2 generation.
For example, after the F2 generation, we receive 3 tall:1 small plants if a tall plant (TT) is crossed with a dwarf plant (tt).
Thus, a monohybrid ratio is 3:1.
In this case, one plant’s height is taken into account at a time.

Dihybrid cross

A dihybrid cross occurs when two organisms are crossed while taking into account two characters.
The dihybrid ratio is the proportion of characteristics that result from this cross at the F2 generation.
For example, if a plant that produces round, green peas is crossed with a plant that produces wrinkled, yellow peas, the resultant plants would all produce round, green peas.
If the same were crossed for an F2 generation, we would see four-character combinations in a 9:3:3:1 ratio.
Consequently, the dihybrid ratio is 9:3:3:1.

Laws of Mendel

According to the Law of Dominance, a gene contains two opposing alleles, of which one manifests itself in the organism consistently.

It is expressed in every conceivable combination and is known as the dominant gene.

The Law of Segregation states that throughout gamete production, characteristics segregate without any allele mixing.

The Law of Independent Assortment states that during gamete production, characteristics can segregate independently of various attributes.

Sex Determination

Sex determination is the process of identifying a person’s sex based on the makeup of their genetic makeup.
Different elements determine an embryo’s sex in different animals.
When it comes to humans, sex is determined by whether or not the Y chromosome is present.
XY is a man, whereas XX is a woman.
An X chromosome is present in every ovum.
An ovum produces a male offspring when it fuses with sperm that contains Y, and a female child when it fuses with sperm that contains X.

Traits

An organism’s traits are its defining characteristics, which can be seen in its physiological makeup or their outward appearance.

Acquired Characters

Acquired qualities are those that an organism develops throughout its existence.
The following generation does not inherit these traits if they are not incorporated into the DNA of germ cells. For instance, starvation-induced muscle atrophy and weight loss, injury-induced loss of limbs or tails, etc.

Inherited Characters

Inherited characters are characteristics that are passed down from parents.
These characteristics are always passed down to the following generation, albeit they may or may not manifest themselves based on dominance or recessiveness.
Height, skin tone, and eye color are a few examples.

Variation

The difference between members of the same species is measured by variation. Children are not exactly like their parents; there are differences. Within a population, every individual is unique. Variations are mostly caused by recombination and mutation.

Individuals of a species that reproduce sexually vary greatly from one another, and the gradual accumulation of these differences is a major factor in evolution. One of the main forces behind evolutionary processes is the selection of variations by environmental influences.

Genetic Variations

Genetic variants are the discrepancies in DNA sequences seen in all organisms that result in a diversified gene pool. Different/varied physical characteristics or metabolic pathways result from these changes.

Natural Selection

It is the process by which a species’ advantageous characteristic is chosen in a population.
All of the current species are under equal pressure from changing environmental conditions.
Natural selection favors those species and organisms that can adapt to changing conditions, and those that are unable to do so perish, being rejected by the natural world.

Speciation

Genetic Drift

The features that endure in a population can be determined in large part by natural selection. On the other hand, random oscillations in gene variations are frequently observed. We refer to this phenomenon as genetic drift. Therefore, a shift in an allele’s frequency within a small population is known as genetic drift.

A gene variant may vanish from the population due to genetic drift, which would decrease genetic variation.

Evolution and Fossils

Evolution

Evolution is the observable shift over numerous generations in a population’s heritable traits. These alterations may result in the emergence of a new species or cause an existing species to alter to better suit its new home.

Origin of Species

Following a triumphant journey aboard HMS Beagle, Charles Darwin penned a book detailing his observations made on the Galapagos Islands.
He penned a thorough theory of evolution, primarily based on natural selection, in the book The Origin of Species.

Evolutionary Relationships

Analogous and homologous organ studies can be used to infer an animal’s evolutionary relationships.

Organs classified as homologous have a similar structure but a distinct function.

Although the forelimbs of mammals and birds have comparable anatomy, their functions are distinct.

Both the pea plant’s tendril and the barberry plant’s spine are modified leaves, yet they serve distinct purposes.

Organs that operate similarly yet differ in terms of their origin and structure are called analogous organs.

Bat, bird, and insect wings are all utilized for flight, yet they differ greatly in structure.
Both opuntia and peepal leaves are used for photosynthesis; however, opuntia leaves are modified stems, whereas peepal leaves are regular leaves.

Human Evolution

It is recognized that humans are members of the ape family. Chimpanzees and other primates have a relatively close genetic ancestor with modern humans.
A more comprehensive picture of human evolution has been constructed, even though the exact process by which humans evolved from primates is still unknown.
Dryopithecus, Ramapithecus, Australopithecus, Homo erectus, Homo sapiens neanderthalensis, Cro-magnon man, and ultimately us, Homo sapiens, are some of the predecessors of modern humans.
The origins of human evolution are in Africa. They then dispersed over the globe.

Check out: CBSE Class 10th Previous Year Papers

How to Use CBSE Class 10 Notes

1. Read the Chapter Carefully: Start by reading the whole chapter from your NCERT textbook. For example, in Chapter 9 (Heredity and Evolution), make sure you understand topics like Mendel’s experiments, how traits are passed down, and how evolution works. 

2. Go Through the Notes: After reading the textbook, use this CBSE Class 10 notes to help you understand the chapter better. Notes are great for summarising important points, like Mendel’s laws or the process of evolution, so you don’t miss out on anything important.

3. Highlight Important Points: While going through the notes of Chapter 9, underline or highlight key terms, such as “dominant traits,” “genes,” “chromosomes,” and “evolution.” This helps you focus on the most important ideas and makes revision easier.

4. Make Simple Short Notes: After you’ve gone through the chapter and notes, make your own shorter version. For example, write down the key points like “Mendel’s law of inheritance” or “stages of human evolution.” These quick notes will be helpful for last-minute revision.

5. Understand, Don’t Just Memorize: It’s important to really understand the ideas instead of just memorizing them. For example, instead of memorizing what inheritance is, try to understand how traits are passed down from one generation to the next.

6. Revise Regularly: Keep going over your CBSE Class 10 notes regularly. Revising helps you remember the information for a longer time. For example, reviewing your notes on evolution or Mendel’s experiments every few days will keep the concepts fresh in your mind.

Check out: CBSE Class 10th Question Banks

Science Chapter 9 Notes FAQs

1. What is heredity?

Heredity is the process through which traits or characteristics are passed from parents to offspring.

2. What are Mendel's Laws of Inheritance?

Mendel's Laws of Inheritance are:

1. Law of Dominance: One allele (dominant) can mask the expression of another allele (recessive).

2. Law of Segregation: Each organism has two alleles for each trait, and these alleles separate during gamete formation.

3. Law of Independent Assortment: Genes for different traits are inherited independently of each other.

3. What is a gene?

A gene is a segment of DNA that carries information for a specific trait, like eye colour or height.

4. What is the role of chromosomes in inheritance?

Chromosomes carry genes, which are responsible for transmitting traits from one generation to the next. They are present in pairs in the cells of living organisms.

5. What is the theory of evolution?

The theory of evolution explains how species change over time through the process of natural selection, where organisms with traits that help them survive in their environment are more likely to reproduce and pass those traits on.