Heredity And Evolution Class 10 Notes

Heredity And Evolution Class 10 Notes

Heredity And Evolution Class 10 Notes

The term heredity can be defined as the transmission of traits to offsprings from parents. These traits are mainly passed through one generation to next generation via DNA, a molecule that encodes genetic information and acts as a genetic material. Mostly all organisms contain DNA as a genetic material except some virus that contain RNA as their genetic material.

Packaging of Hereditary Material in Eukaryotes and Prokaryotes 


Eukaryotes have well organised nucleus and membrane bound organelles. The nucleus has four main components such as nuclear envelope, nucleoplasm or karyolymph. chromatin and nucleolus. 

Prokaryotic nucleus is undefined or unorganised as it is without nuclear membrane. Hence, it is called nucleoid or chromatin body. The chromosomes of bacteria are constituted by circular DNA. Though bacteria do not have histones, usually DNA is associated with several types of proteins that bind to the phosphate group of DNA.

DNA (Deoxyribonucleic Acid)

  • DNA is a long polymeric structure of deoxyribonucleotides. The number of nucleotides present in it mainly define its length.
  • Chemically, DNA nucleotide consists of three components namely nitrogenous base, a pentose sugar (ribose in case of RNA and deoxyribose for DNA) and a phosphate group. 
  • The nitrogenous bases are mainly of two types, i.e.. purine (adenine and guanine) and pyrimidine (cytosine, uracil and thymine). 
  • Adenine, (A) Guanine (G), Cytosine (C) are usually present in both RNA and DNA but thymine is replaced by uracil in RNA. 
  • A nitrogenous base is linked to pentose sugar (CsH002) through a N-glycosidic linkage to form a nucleoside such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxyuridine.
  • When a phosphate group is linked to 5-OH of a nucleoside through a phosphodiester linkage, a corresponding nucleotide is formed which is usually known as the basic repeating unit of DNA.
  • DNA in structural appearance look like a helix (right-handed) coiled by two strands having anti-parallel polarity, one is having 5′-3’and that of other is 3′-9 These two strands are complementary to each other and always follow A-TC-G base pairing and vice versa.
  • The coding segment of DNA is called exon and introns are the intervening sequences that do not appear in a mature or processed RNA.
  • Double helix model of DNA was given by Watson and Francis Crick in 1953. Its understanding is based on X-ray diffraction data produced by Mauric Wilkins and Rosalind Franklin

Various Forms of DNA 

DNA of some viruses such as *174, which attacks E. coli is  single stranded On the basis of number of nucleotide residues. DNA is classified into three types as follows 

A-DNA liis double helical DNA having 11 residues per turn It has a right handed helix

B-DNA This is the Watson and Crick double helix having 10 residues per turn it is also right handed 

Z-DNA it is a left handed double helix having 12 residues per turn.

RNA (Ribonucleic Acid)  

  • It was considered as the first genetic material. It acts as genetic material in some viruses and also as a catalyst in some biochemical reactions. DNA is said to be evolved from RNA. 
  • Structurally RNA is single stranded, generally made up of different molecules of pentose sugar and phosphate group linked together.
  • RNA occurs in different forms i.e., messenger RNA (MRNA), ribosomal RNA disha (TRNA) and transfer RNA (RNA).
  • RNA can be genetic or non-genetic. 

Central Dogma 

This was given by Francis Crick. According to this phenomenon, the genetic information flows in a forward direction, i.e., from DNA + RNA → Protein.



that the Dist Evolution is defined as the sequence of gradual changes from simple life forms to complex life forms, i.e., from primitive organisms that existed over million of years to new organisms that exists today. It is all about changes, improvement and modification from Sample lile forms.

Origin of Life 

Scientists hypothesise that the universe came into existence about 15 billion years ago with. I clossal explosion often referred to as the big bang theory. 

This theory antempts to explain the origin of universe, approximately 20 billion years ago. nen the universe was very hot and dense and expanding rapidly. After initial expansion energy conversion had occurred to form various subatomic particles Including protons , neutrons and electrons. With the cooling universe , after thousands of years , some other reactions lead to the formation of first electrically neutral atoms.

The atoms formed by big bang were hydrogen, helium and some traces of lithium. 

Mainly it was known that life originated approximately 3,600 million years ago. This was evident by the discovery of fossil of cyanobacteria. The early thought was that living things arose from non-living things, i.e., spontaneous generation, which was disproved by Louis Pasteur. 

The most widely accepted theory of ‘origin of life’ was given by AI Oparin, JBS Haldane SL Miller and SW Fox that states that life originated or earth through physiochemical processes of atom that combined to form molecules, to produce inorganic and organic compounds.

Biological Evolution 

It is a biological process that occurs in an individual or group of living organisms. The time living population takes to evolve depends on the reproduction time of the organism. This evolution mainly occurs at a genetic level i.e., change in frequency in a population from one generation to the next. 

Theories of Organic Evolution 

The term organic evolution means a gradual continuous process of variation over a long period of time. Evolutionary biological system basically includes, both the origin of life and diversity of living organism on the earth. 

Some theories that explain the scientific basis or organic evolution are


Jean Baptiste de Lamarck (1744-1829) was the first who had given theory of evolution. He published his famous book ‘Philosophie Zoologique’ in 1809. Lamarck had mainly put light on the concept of evolution and provided two main ideas. 

(i) Theory of use and disuse, i.e., the body parts used more often become stronger an larger, while the parts that are not used gets degenerated and disappear. 

(ii) Inheritance of acquired characters, i.e., the physiological changes acquired over the life of an organism may be transmitted to offspring and hence called the theory of adaptation.

Lamarck illustrated his idea through an example of giraffe, that initially do not have long necks. But in order to reach the leaves on tall trees, they adapted the elongation of their necks and passed this acquired character to their succeeding generation over years. This moyo no more accepecu now.


The most impressive study on evolution was made by Charles Darwin in his book on The Origin of Species by means of natural selection or the preservation of favoured race in the struggle of life. Charles Darwin (1809-1882) was an English naturalist. In 1813, he got an opportunity to travel on HMS Beagle (a ship) on which he sailed around the world. 

Darwin found a living laboratory of evolution in Galapagos Islands and found closely related species of finches known as ‘Darwin’s finches’.

The common bird of Galapagos islands, the finches were markedly different from the Finches of the main land. Form this island only , he took an idea for his theory of natural selection.

Key information about Darwin’s natural selection 

  • The rate of appearance of new forms is linked to the life cycle or life span.
  •  Nature selects for fitness, based on characteristics which are inherited. 
  • There is always a genetic basis for getting selected and to evolve.
  • Organism adapt to survive in an otherwise hostile environment. 
  •  Adaptive ability is inherited, i.e., on the basis of genetics.
  • Fitness is the end result of the ability to adapt and get selected by nature. 

Mutation Theory 

Hugo de Vries (1848-1935), a Dutch botanist, found mutation in evening primrose (Oenothera lamarckiana) and proposed that the new species arise by sudden variations. Salient features of mutation theory are 

(i) Evolution is a jerky process where new varieties and species are formed by  mutations. 

(ii) Mutation or discontinous variations are the raw material for evolution. 

(iii) Mutation may be sudden or operational. 

(iv) All mutations are inheritable. 

(v) One type of mutation can appear in different individuals.

Agents of Evolution

Evidences of Organic Evolution 

 Various evidences in support of organic evolution come from different sources as given 

Evidences from Morphology and Comparative Anatomy 

1.Homologous Organs These are the organs having same embryonic origin and basin structure but have different functions.e.g, forelimbs of frog, bird and human. 

(ii) Analogous Organs These are the organs having similar functions but different in embryonic origin and basic structure. e.g., wings of insects and birds. 

(iii) Vestigial Organs These are non-functional organs which were functional in the ancestral forms e.g., underdeveloped limbs of snakes, feathers of kiwi, human skin hair, vermiform appendix, etc. Sudden reappearance or refunctioning of some ancestral organs is called atavism or reversion. 

Evidences from Connecting Links 

A number of organisms have characteristics of two different groups, thus are called connecting links. 

 Some Examples of Connecting Link


OrganismConnecting Link (in between).
Euglena (Protozoa)Animal and plant
Proterospongia (Protozoa)Protozoa and Porifera
Peripatus (Arthropoda);Annelida and Arthropoda
Neopilina (Mollusca)Annelida and Mollusca
Balanoglossus (Chordata)Non-chordata and Chordata
Dipnoi (Lung fish)Pisces and Amphibia
Archaeopteryx (Aves)Reptiles and Aves
Prototheria (Mammalia)Reptiles and Mammalia

Evidences from Genetics 

Different hybrid varieties of any particular species show close resemblances to their close relations. e.g., mule originated from hybridisation of horse and donkey.

Evidences from Embryology 

The theory of recapitulation or Biogenetic Law was proposed by Haeckel. It states that an individual in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny) i.e., ‘Ontogeny recapitulates Phylogeny. Organisms of different groups resemble with their embryos. 


Remains of ancient lives, as bone, teeth, shale, etc are called fossils. These are generally found in sedimentary rocks. Age of fossil is determined by lead-uranium method, carbon dating method, Fission track and electron spin resonance methods. Coprolites are fossils: with faeces containing salt of phosphates.

Origin and Evolution of Man

The evolutionary process leading to the appearance of modern humans, is known human evolution. This evolutionary process shows changes and development series  human with time.

Dryopithecus20-25 million years agoThey were ape-like in appearance and were hairy having arm and legs of same length, large brain and walked like gorillas and chimpanzees.
Ramapithecus15 million year agoThey were more man like and are also hairy, walked like gorillas and chimpanzees.
Tanzania3-4 million year agoThey were smaller than 4 feet and walked upright and appear man like primater.
Australo pithecines or Homohabilis2 million year agoThey were articularlyate fruits not meat. They have brain capacities of between 650-800 cc. They use stone weapons for hunting. They appear like humans.
Homon erectus (Java man)1.5 million year ago They were probably meat eaters and have brain capacity of around 900 cc.
Neanderthal man (Primitive man)100,000-40,000 years backThey have the brain capacity of 1400 cc. They used hides to protect themselves and buried their dead.
Homo sapiens (Modern man)75000-10,000 yearsAfter last glacial period or ice age modern man have evolved. They have brain capacity of 1450 cc.
  • First mammals were like shrews. 
  • Dinosours were considered as land reptiles and biggest of them was Tyrannosaurus rex, about 20 feet in height. 
  • Mammals were viviparous and protected their unborn young ones inside mother’s body.
  •  Lobefins evolved into first amphibians that lived on both land and water. These
  • were considered as the ancestors of modern frog and salamanders.
  • It is believed that in future, human could change due to various factors like gene mutation, gene recombination, natural selection, etc. HL sapiro named the future man Homo sapiens futuris.

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