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

Heredity and evolution is a very important biology chapter of the NCERT Class 10th from an exam point of view. The NCERT Class 10 Science Chapter 9 notes give you a basic idea of the chapter heredity and evolution. The main topics covered in Chapter 9 NCERT Class 10 Science notes are definitions, examples, accumulation of variation during reproduction, heredity - inherited traits, Mendel’s rules for the inheritance of traits, how do these traits get expressed?, sex determination, EVOLUTION, Acquired and Inherited Traits, speciation, evolution and classification, tracing evolutionary relationships, fossils, evolution should not be equated with progress, and Human evolution. Download the CBSE Notes for Class 10 Science, Chapter 9, PDF to use offline anywhere. Students must go through each topic in the heredity and evolution in Class 10 Notes Science in the easiest and most effective way possible with the help of NCERT Notes for Class 10.

Class 10 Science chapter 9 notes also cover all the important concepts related to evolution and heredity, which are useful in various competitive exams. Heredity and evolution NCERT Notes for Class 10 Science help you revise these major concepts given in the NCERT Book in no time during CBSE Board exam preparation. CBSE Class 10 Science Chapter 9 notes will help you with quick revision. The Heredity and Evolution chapter covers all headings of NCERT Textbook. CBSE Class 10 Science chapter 9 notes also contain important examples that have been frequently asked in the various exams. Having revision notes and NCERT Solutions for Class 10 Chapter 9 handy is beneficial to save you time. The NCERT Class 10 notes pdf can be downloaded through the link given below.

Also, Students can refer to:

• NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution.
• NCERT Exemplar Class 10 Science Chapter 9 Solutions Heredity and Evolution

NCERT Class 10 Chapter 9 Class Notes

Heredity and Evolution

• This chapter deals with variation that occurs in organisms during reproduction.
• Variation is maximised by the process of sexual reproduction.
• If we observe the field of sugarcane, then we find very little variation among the individual plant, but in animals including human beings which reproduce sexually quiet distinct variations are seen among different Individuals.

Lets learn about the mechanism by which variations are created and inherited with NCERT notes for Class 10 Science chapter 9

Accumulation of Variation during Reproduction

• Asexual reproduction involves only one Parent.

• An organism inherits the character of only one Parent.

• As a result, Offsprings are almost carbon copies of parents, Called Clone.

• E.g. Asexual reproduction in Bacteria, Yeast, Amoeba, etc.

• Sexual reproduction involves two parents- Male and Female.

• Similarities, as well as subtle differences, are inherited.

• This leads to variation among individuals of a new generation.

• If this new generation reproduces, second-generation produced accumulate more variations.

• Some variations inherit from first-generation and some are newly created.

• Variation leads organisms to adapt to different environmental conditions and increases the chances of survival.

• E.g. Some variants of bacteria survive in extremely hot conditions and some in cold conditions.

• Inheritable Variation leads to the evolution and formation of new species.

An organism at the top gives rise to two individuals with similar Body designs but with a subtle difference. Each of them, then give rise to two individual in the next generation. Each of the four individuals at the bottom is Different from each other. Some of the differences will be unique and others are inherited from their respective Parent who is different from each other.

Heredity

• Process of transmission of genetic characteristics from one generation to another.
• Offspring differ from each other and from their parents In a few characters.

Inherited Traits:

• Offsprings Produced by sexual reproduction are also similar to their parents.
• E.g. Egg laid by Crow Hatch into a crow and Human Child bears All basic character of human beings.
• Traits that are inherited from Parents to Offspring are called inherited Traits.
• The genes present on chromosomes are responsible for the inheritance of traits.

Genetics Terminology

• Genome: Total number of genes present in the haploid set of chromosomes.
• Progeny: Offsprings Produced by mating called Progeny.
• Factor: Genes located on the chromosome are known as a factor. The term used by Mendel is for carriers of hereditary information.
• Locus: Location of a particular gene on a chromosome.
• Alleles: Two alternative forms of unit factor
• Homozygous: Identical alleles on the homologous chromosome
• Heterozygous: Different alleles on the homologous chromosome
• Dominant allele: Allele that expresses in both Homozygous and Heterozygous conditions. Represent by Upper case letter. (T)
• Recessive allele: Allele that Is not expressed in Heterozygous conditions. Represent by lower case letter. (t)
• Genotype: Genetic makeup of an organisms
• Phenotype: Observable character. E g.- Tall or Dwarf is phenotype characters.
• F1 Generation: First filial generation.
• F2 Generation: Second filial generation.

Gregor Johann Mendel:

• Father of Genetics.
• Born in 1822.
• In 1856, Mendel perform the first set of experiments with Garden Pea.
• In 1884, Mendel died due to a kidney disorder.

Why did Mendel Select Pea Plants for His Experiment?

• The short life cycle of 2-3 Months
• It has many contrasting traits
• Natural self-pollination present
• Easy to cultivate
• Cross-pollination can be performed artificially so hybridization can be possible.
• offspring can be analysed within a short period of time.

The Reason Behind Mendel's Success:

• Studied the inheritance of one or two characters at a time.

• Selection of material

• Maintains statistical records of all the experiments.

Mendel Experiment Technique:

• Selection of pure parent plants
• Hybridization of the parent plant to produce F1 Generation
• Raising of second-generation(F2) by self-fertilization of a hybrid produced in the F1 generation.

Monohybrid Cross:

• Cross between two individuals who differ in only one pair of contrasting traits.
• Studied the transmission of only one character from one generation to other.

Dihybrid Cross:

• Cross involves two pairs of contrasting traits.
• Mendel considered the inheritance of two different characters simultaneously.

How Do these Traits Get Expressed:

• DNA is the information source for making protein in the cell.

• Section of DNA that provides information for a particular protein is called gene for that protein.

• The character of an organism is controlled by protein.

• E.g. Height of a plant depends on the amount of Particular Plant hormone. The amount of hormone produced Depend on the efficiency of an enzyme involved in its production.

• If enzymes work properly, the required amount of hormone is produced and the plant will be of normal height.

• If any change occurs in the structure of the gene Of a specific enzyme. Then the required amount of hormone will not produce and it will affect the height of the plant.

• Thus, Gene Control Characteristics or Traits.

Sex Determination

• The mechanism by which the sex of an individual is determined is called sex determination.

• In a human being, Sex is determined by chromosomes inherited from male parents to determine whether the Offsprings will be boy or girl.

• Chromosomes are of two types:

Sex Chromosome:

• Chromosome Associate with sex determination is called sex Chromosome.
• Carry genes for sexual characters.
• Women have a pair of sex Chromosomes both called ‘X’
• Men have a mismatched pair of sex chromosomes ‘XY’

Autosome:

• Chromosomes other than sex chromosomes are called autosomes.
• Humans have 22 Pairs of Autosomes.

Evolution and its Mechanism

The sequence of gradual change that takes place in the organisms over millions of years and lead to the origin of new species.

Mechanism of Evolution:

• Consider a group of 12 red beetles and assume that they live in bushes Of green leaves. They undergo sexual reproduction and generate a variation. Crow eat these beetles. A large number of beetle were eaten up by crows and fewer are available for reproduction.

Assume The Following Situation:

• Survival Advantage: Assume that some beetle develops colour variation during reproduction. One beetle acquired green colour instead of red due to variation. When green beetle reproduces it passes green colour to their offspring. Crows are not able to see green beetle on green leaves hence they are not predated. Therefore, the Chance of survival increase for green beetle. But Progeny of red beetle Continued predated by a crow. Hence, the Green beetle was naturally selected over the red beetle.

• Suppose another colour variation occurs in beetle and blue coloured beetle arises accidentally. Crow sees both of them and eats. Suppose an Elephant comes and by stamp kill most of the red beetles, while some blue beetle survive. Here, the accidental survival of blue beetle and the frequency of their genes increases. Here colour Change gave no survival advantage. In a small population, evolutionary variation in the allelic frequencies is called genetic drift.

• Consider the example of a beetle. Its population starts expanding by sexual reproduction. A plant disease spreads resulting in a decrease in the amount of leaf material. The population of beetle is now poorly nourished and the average weight of beetle decreased compared to those beetle when leaves in the plant are in plenty. After some time, Plant diseases are eliminated. Now, more leaves are available as food for beetles. So the average weight of beetle again increases.

• While considering the third situation, There are two kinds of Traits in every organism.

Inherited Traits:

• Traits are controlled by specific genes and passed on from one generation to another through germ cells.

Acquired Traits:

• Traits that are gained During the lifetime are called acquired traits.

• These cannot be Passed on to progeny as these traits influence only somatic cells, not germ cells.

• Some of the generations of beetles are low in weight because of starvation, this trait cannot be inherited to progeny over a generation.

• Other E.g.- Removal of tail In the consecutive generation of mice, Pierced ears, are the lifetime experience of the individual.

Speciation

Splitting of one species into two or more species over a period of time due to geographical barrier or reproductive isolation.

Reproductive isolation happens due to:

• Breed at different times

• Change in number of chromosomes

• In the case of beetle, Green females are not able to mate with a red male but only with a green male. Her behaviour will ensure that there is no reproduction among them. Effectively, New species of beetle are being generated.

Evolution and Classification

• Classification is the arrangement of organisms into groups and subgroups on the basis of their similarities and dissimilarities.

• Two species that have more common characteristics are more closely related.

• More closely they are related means they are emerged from the common ancestor.

Evolutionary Relationship:

• Relationship between different organisms or species on the basis of evolutionary history.

Tracing Evolutionary Relationship:

• A number of evidence are provided by the organism which helps in tracing Evolutionary relationships. These are:

Comparative Morphological Evidence:

• Evidence-based on similarities in internal and external features.

Homologous Organ:

• Organ similar in origin but differ in function and external structure.

• Organ shows common ancestry and proves divergent evolution As these organs are modified to perform the different functions as adaptation.

• E.g. Forearm of humans, the wings of a bat, the Flippers of whales, and the forelimb of other vertebrates.

• In plants, Thorn of bougainvillea and Tendrils of cucurbita are e.g. of homologous organ

Analogous Organ:

• Organs are similar in function but differs in origin

• Do not show common ancestry, but show convergent Evolution.

• E.g. Sting of bee and scorpion, wings of bird and butterfly, Wings of birds and bat.

Fossils:

• The impression remains, and traces of past organisms found in sedimentary rocks, peats, lava, and snow are called Fossils.

• Fossils are past evidence of an organism that is prevented in the earth’s crust.

• Fossils also provide evidence for evolution.

• E g. Fossils of Archaeopteryx Look like primitive birds.

Determination Of The age Of Fossils:

• Fossils closer to the surface are more recent than the fossils found in deeper layers.

• In radioactive isotope dating of fossils, the ratio of different isotopes of the same element is used in dating fossil material. E g. Carbon dating, Uranium dating

Evolution By Stages:

• Complex organs present in the body of complex multicellular organisms are not formed by a single DNA change in a single generation but created slowly in several generations.

• From the fossil records, it is concluded that evolution has taken place from simple to complex structures in a gradual manner.

Evolution of wild cabbage by artificial selection

Evolution Should Not Be Equated With ’Progress’

• Evolution should neither be equated with progress nor with the elimination of older.

• New species formed may or may not be better.

• The formation of new species depends on the reproductive barrier, genetic drift, and natural selection.

• Evolution does not proceed continuously in one direction.

• Evolution is the generation of diversity and shaping of diversity by environmental selection.

Progressive and Retrogressive Evolution:

Progressive Evolution:

• Formation of complex structure from the simple structure.

• E.g. Formation of amphibians from fish.

Retrogressive Evolution:

• Formation of simple structure from the complex structure.

• E.g. Flightless bird from a flying bird.

Evolution Is Not Always Progressive:

• During Evolution, new species are formed and an original one also exists.

• Natural selection and genetic drift together lead to the formation of a new population that can’t reproduce with the original one.

• Give rise to the formation of new species.

• New species may or may not have an advanced character than the original one.

• The trend may be retrogressive or progressive.

Human Evolution:

• Human Evolution can be studied With help of evolutionary tools Such as Fossils, Time dating, and By determining DNA Sequence.

• Recent evidence - based on a genetic basis clearly indicates that the origin of man occurred in Africa.

• From Africa, the Human species Spread to a different region.

• Like all other species, Humans are also the result of evolution.

Chapter-Wise NCERT Class 10 Notes Science

Significance of NCERT Notes for Class 10 Science Chapter 9

Class 10 Heredity and Evolution Notes Will be helpful to revise the chapter and understand the important topics of the chapter. These Notes for Class 10 science chapter 9 are also beneficial for covering the core concepts of the CBSE Class 10 Syllabus 2024 PDF as well as for competitive exams such as AIPMT, NEET, AIIMS, and other similar exams.

Subject Wise NCERT Solutions

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