Heredity and Evolution Notes

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HEREDITY AND EVOLUTION NOTES

Heredity and Evolution Notes

Basic Concepts –

  1. Gene – It is the basic physical and functional unit of heredity.
  2. Chromosome – It is a DNA molecule that consists of a part or all of the genetic material of an organism. OR  It is the microscopic threadlike part of the cell that carries hereditary information in the form of genes.
  3. Nucleosome – It is any of the repeating subunits of chromatin, consisting of a DNA chain coiled around a core of histones.
  4. Nucleotide – It is an organic molecule with a basic composition of a nitrogenous base, pentose sugar and phosphate.

Heredity: 

Transfer of characters from parents to offsprings via genes

Uses of study of heredity:

  1. Diagnosis of hereditary disorders.
  2. Treatment of diseases
  3. Prevention
  4. Production of hybrid varieties
  5. Microbial use in processes
Year Scientist Area Discovery
1886 Mendel Pioneer of modern genetics Pea plant experiments
1901 Hugo de Vries Mutation Reasons of sudden changes
1902 Walter  Sutton Study of chromosomes Chromosomes in grasshopper
1944 Ostwald Avery, Mclyn McCarthy, Colin McLeod DNA All living organisms have DNA
1961 Francois Jacob, Jack Monad Protein synthesis Model of protein synthesis

 

CENTRAL DOGMA Heredity and Evolution Notes

 

  • It explains the flow of genetic information from DNA
  • Explains flow of genetic information from DNA to RNA to make protein.
  • The information about protein synthesis is stored in DNA and for proper functioning of body, synthesis of appropriate protein is necessary.
  • The synthesis of proteins by DNA through RNA is called central dogma.
  • Occurs in three steps – Transcription, Translation, Translocation.

1.Transcription:

  • It is the process of synthesis of mRNA from DNA
  • Takes place in presence of RNA polymerase
  • The information from DNA is copied from one molecule to another 
  • DNA creates mRNA to deliver its information out the nucleus
  • First, the double helix of DNA is unwound by RNA polymerase
  • As the double helix unwinds, ribonucleotide bases (A, C, G, U) attach the molecules of DNA strand by complementary base pairing by covalent bonds and then it recoils.
  • When it is released from DNA, the mRNA now comes in cytoplasm with the coded message from DNA
  • The message contains codes for amino acids which consist of 3 nucleotides. hence, they are called triplet codons.

2.Translation: Heredity and Evolution Notes

  • Once the mRNA has left the nucleus, it is directed to a ribosome to construct a protein.
  • Ribosome attaches to the mRNA molecule.
  • tRNA act as couriers as per the message on mRNA, amino acids are supplied by tRNA.
  • tRNA has anticodon having complementary sequence to the codon on mRNA
  • The amino acids brought in by tRNA are bonded together by peptide bonds with the help of rRNA

       

3.Translocation:

  • During the process of translation, the ribosome keeps on moving from one end of mRNA to the other by the distance of one triplet codon, it is called translocation.
  • The long chains of amino acids come together to form complex protein.
  • Many polypeptide chains come together to form different proteins.

MUTATION

Definition – Sudden change occurring in the genetic material is known as mutation.

During transmission of genes, some genes are transmitted without change

However sometimes sudden changes occur in the genes.

Any nucleotide of the gene changes its position causing a minor change.

Reasons / Mutagens (Agents that cause mutation)

  1. Radiations like UV radiations, X-rays
  2. Chemicals – chemicals released during smoking, food preservations, barbecuing, chemicals like Benzoyl peroxides (an important constituent present in acne products)
  3. Infectious agents – HPV, Contaminated food
  4. Natural factors

Types –

They are of two types –

  1. Major
  2. Minor

Ex.

Normal sequence –     C T A G

Insertion (genes are added) – C G T A G

Deletion (Genes are deleted) – C T G

Inversion (sequence changed) – C A T G

Duplication (Genes are repeated) – C T A T A G

Effects –

  1. It brings about various genetic disorders like sickle cell anaemia, cancer
  2. Formation of new character or trait.Ex. Albinism
  3. Formation of extra body part.

EVOLUTION –

  • It is presumed that the universe came into existence with a single explosion called big bang about 15 billion years ago.
  • With this big bang, all the matter and energy came into existence.
  • The fragments of the fire ball expanded and cooled and the celestial bodies

Origin of earth –

  • The earth is formed about 6 billion years ago.
  • It was broken from the sun.
  • Initially it was a glowing fire and rotating cloud of hot gases.
  • As the earth was moving away from the sun, its temperature slowly decreased.
  • The gases got condensed.
  • Heavy elements like iron, nickel, etc sank to the centre and formed solid core of earth.
  • The lightest elements like hydrogen, helium, etc occupied the atmosphere.

Evolution:

  • The gradual changes occurring in living organisms over a long duration is called evolution
  • It results in development of organisms
  • It is a slow-going process
  • It is formation of new species due to changes in specific characters
  • The changes get accumulated over several generations in response to natural selection.

Origin of life:

Heredity and Evolution Notes

  • Life originated on earth 3.5 billion years ago.
  • At the beginning, only simple elements were there in the ocean (like H, O, N, C, etc)
  • From these, formed simple organic and inorganic compounds like ammonia (NH3), methane (CH4), amino acids, fatty acids, purines, pyrimidines, etc
  • Then after that, complex compounds like proteins and nucleic acids formed due to the reactions between simple compounds.
  • This step was followed by formation of precells.
  • The nucleic acid in pre cells gradually started series of reactions like protein synthesis. From these, first primitive cells formed.
  • Their number increased by utilizing surrounding chemicals
  • Varieties developed.
  • Living organisms developed
  • Organisms which were able to adapt to surrounding conditions, survived and grew
  • Those who could not adjust, perished.
  • This is called Theory of Gradual development.

THEORY OF EVOLUTION –

  • According to this theory, the first living material was Which was formed in oceans.
  • From this, unicellular organisms developed.
  • After almost 300 crore years later, gradual changes occurred in the unicellular organisms and larger and more complex organisms developed.
  • All round and multidimensional changes occurred in them which resulted in formation of plants animals from ancestors having different structural and functional organization.
  • Progressive development of plants and animals from the ancestors having different structural and functional organization is called

EVIDANCES OF EVOLUTION –

The various proofs supporting the theory of evolution are called evidences of evolution.

1.Morphological evidence –

  • These are the evidences based on similarities in the external structures.
  • If we compare various animals like dogs, cat, tiger, etc. we find that all these animals have certain similarity in their size, shape and structure of organs like, all are having 2 eyes, 2 ears, 1 tail, 2 pairs of limbs, etc.
  • In case of plants, all plants have basic common structures like root, stem, leaves, etc. in spite of various differences.
  • This indicates, they have evolved from a common ancestor.

2.Anatomical evidences –

Heredity and Evolution Notes

  • Study of internal structures – anatomy
  • These are the evidences based on similarities in the internal structures of different kinds of organisms.

 

Arm of human, wing of bird / bat, leg of cat, flipper of whale/ dolphin.

These organs perform different functions in these organisms but they have similarity in their bony structures and joints which indicates their common ancestor.

3.Vestigial organs –

  • Degenerated or underdeveloped organs present in an organism.
  • The organs undergo changes during evolution process.
  • Due to natural selection, they undergo degeneration and they vanish from the body after a long time.
  • Even though, they are non-functional in some organisms, they are functional in others.
  1. Appendix – It is functional in grass eaters for digestion of cellulose in food.
  2. Ear muscles – Useful in animals like monkeys, cows, etc for movement of ears.
  3. Tail bone / Coccyx – Functional in animals having tail.
  4. Body hair – Useful for insulation of body in animals
  5. Wisdom teeth – It is functional in grass eaters for digestion of cellulose in food.
  6. Nictitating membrane / Plica semilunaris / third eyelid.

4.Paleontological evidences-

  • Palaios – old / ancient; ontos – being; logas – study.
  • Paleontology – study of past life based on fossil record.
  • Fossils – dead remains of plants and animals that lived in the past.
  • Due to various natural calamities like earthquake, landslides, various living organisms get buried deep down the earth surface.
  • The remnants and impressions of these organisms remain preserved underground.
  • These are either formed in sedimentary rocks, peat, amber, ice, soil, lava, etc.

PROCESS OF FOSSIL FORMATION –

  • Igneous rocks (formed by solidification of lava) à sedimentary rocks à dead animals / plants carried out to sea by river à settle at the bottom à buried in sedimentary rocks / mud à oxygen deficiency à prevents complete decomposition àremain buried à fossils à after millions of years the fossils get exposed due to factors like erosion

CARBON DATING METHOD –

  • Developed by Willard Libby
  • It is the technique with the help of which we can understand the age of fossils.
  • Living organisms continuously interact with each other and exchange carbon.
  • When they are dead, this process of carbon consumption stops completely.
  • The carbon is present in 3 main isotopes – C-12, C-13, C-14. Of these, C-12 and C – 13 are comparatively stable while C-14 is quite unstable and undergoes continuous decay after the death of organism.
  • Thus, the ratio of C-14 to C-12 changes continuously.
  • Age of fossils can be calculated by measuring radioactivity of C-14 and the ratio of C-14 to C-12 present in the body. 
  • According to structure of earth crust, fossils of various organisms occur at various levels.
  • The oldest fossils are obtained at the depth while the relatively recent ones occupy the upper surface.
  • The fossils of invertebrates were buried in deep layers and belong to Palaeozoic era. The fossils of Pisces, Amphibians and reptiles were obtained in next layers. The Mesozoic era was obtained by reptiles and Cenozoic era showed presence of Aves and Mammals.
  • Thus, with the help of fossils, we get information about our ancestors

5.Connecting links:

Heredity and Evolution Notes

These are some plants and animals that show morphological characters by which they can be related to 2 different groups.

a.Peripatus: 

  • Connecting link between Annelida and Arthropoda.
  • Annelid characters: segmented body, thin cuticle, parapodia like organs for locomotion
  • Arthropod characters: trachea for respiration, open circulation
  • From this, we can conclude that, arthropods have evolved from annelids.

b.Duck Billed platypus:

  • Connecting link between reptiles and mammals.
  • Reptilian character: lays eggs
  • Mammalian characters: presence of mammary glands and hair on body.
  • From this, we can conclude that, mammals have evolved from reptiles.

c.Lungfish:

  • Connecting link between fishes and amphibians.
  • Amphibian character: lungs for respiration.
  • Pisces character: fish like body
  • From this, we can conclude that, amphibians have evolved from fishes.

6.Embryological evidences –

  • Study of embryo is called embryology.
  • Embryo – An embryo is the early stage of development of a multicellular organism. (Up to 8 – 10 weeks of pregnancy)
  • Comparative study of development in different sexually reproducing organism shows that there are extreme similarities during initial stages and those similarities decrease gradually.
  • This indicates that, all these have evolved from a common ancestor.

 

DARWIN’S THEORY OF NATURAL SELECTION –

Heredity and Evolution Notes

  • Charles R. Darwin was a British naturalist.
  • Postulated – “Theory of Origin of Species by natural selection.
  • This theory is also known as Darwinism.
  • It is the most widely accepted theory.
  • During his journey on Galapagos Island, he observed various types of plants and animals.
  • He published a book – ‘Origin of Species’

Principles of Darwin’s theory –

  1. Over production –
  • Every living organism has great potential for reproduction.
  • All organisms produce more young ones than those can survive up to maturity.
  • If all these animals survive, there will be no space for other organisms.
  • Regardless of more rate of reproduction, their number remains constant.

2.Struggle for existence –

  • Even though the individuals reproduce prolifically, the space and food remain constant.
  • This leads to competition among them called struggle for existence.
  • This struggle may be intra specific, inter specific or environmental
  1. Intra specific struggle – competition among individuals of same species (Ex. Lion v/s Lion)
  2. Inter specific struggle – competition among individuals of different species (Ex. Lion v/s Tiger)
  3. Environmental struggle – Struggle of all living organisms with environmental conditions

3. Variation and heredity –

  • These are the differences between individuals of the same species.
  • They may be useful, harmful, neutral.
  • Useful variations are passed on to next generation

4. Survival of the fittest / Natural selection –

  • The organisms with favourable variations succeed and organisms with unfavourable variations perish.
  • This means survival of the fittest.
  • Here, nature selects fit organisms. Hence, it is called natural selection.

5. Origin of species –

  • As a result of these, the organism is better adopted to the environment.
  • The natural selection operates for several generations.
  • In each generation, there is slight betterment of characters.
  • Thus, new species are formed due to gradual accumulation of favourable variations for a number of generations.

Objections to the theory:

  • Natural selection is not the only factor responsible for evolution.
  • He did not mention any explanation about inheritance of useful and useless modifications.
  • No explanation about slow and abrupt (fast) changes was given. 

Lamarckism-

Heredity and Evolution Notes

  • Jean Baptiste Lamarck.
  • Theory of inheritance of acquired characters.
  • Based on concept of Use and disuse of organs.
  • Morphological changes occurring in living organisms are responsible for evolution.
  • The reason behind those morphological changes is activities or laziness of that organism.
  • All organisms can transfer aquired characters to next generation – Ancestry of acquired characters

Examples:

  • Long neck of giraffe is due to browsing on leaves of tall plants.
  • Wings of Ostrich became weak due to no use.
  • Snakes lost limbs due to burrowing habit.
  • Shoulders of ironsmith become strong due to frequent hammering.
  • Legs of ducks have modified for swimming.

Objections:

      Modifications are not always transferred to next generation

Speciation:

Heredity and Evolution Notes

It is the formation of new species of living organisms due to evolution.

Species: It is the group of organisms that can produce fertile individuals through natural reproduction.

Ex. Tiger, Lion, Cat, Dog, etc.

Each species has its own specific geographical conditions, food, habitat, reproductive ability, period, etc.

Factors responsible for speciation:

  1. Genetic variation – Change in genetic constitution of living organisms due to factors like mutation
  2. Geographical changes- Change in geographical conditions in which the organism is living.
  3. Reproductive changes – Changes in reproductive structures,
  4. Isolation – Separation of a single population into several parts / groups

Isolation may be of 2 types: geographical and reproductive.

Geographical isolation:

Separation due to geographical barriers like rivers, mountains, ocean, valley, Iceland, forest, etc.

These barriers prevent interbreeding between the separated groups. The separated groups are exposed to different environmental factors and new characters are developed in them. Thus, new species are formed.

Ex. Darwin’s finches

Reproductive isolation:

Change in genetic material and structure of genital organs.

HUMAN EVOLUTION –

Heredity and Evolution Notes

  • It began approximately 7 crore years ago.
  • The last dinosaurs disappeared 7 crore years ago.
  • Ancestors of humans developed from animals which resembled modern lemur like animals.
  • After about 4 crore years ago, in Africa, the tails of these monkey-like animals disappeared gradually.
  • From these, developed ape–like animals (Aegyptopithecus) due to enlargement of brain and improvement in hand functioning.
  • Some of the Aegyptopithecus migrated to South and North East Asia from which apes like Gibbons and Orangutan developed.
  • While some stayed in Africa which developed into Gorilla and Chimpanzees around 2.5 crore years ago.
  • From these, developed Dryopithecus.
  • 2 crore years ago, human like animals who used hands for eating and other work were evolved.
  • Due to reduction in forests, the apes started living on land.
  • Due to this, there were changes in the structure of their vertebral column and lumbar bones.
  • Thus, they were able to stand in an erect posture and their hands became free for use.
  • The first record of human like ape in East Africa was Ramapithecus (About 1 crore years ago)
  • Around 40 lakh years ago, these apes grew in size and became more intelligent (Australopithecus)
  • Around 20 lakh years ago, human like animals shared morphological similarities with the members of genus homo, and skilled human developed.
  • Around 15 lakh years ago, human walking with erect posture evolved that may have existed in China, Indonesia and Asian subcontinent.
  • Neanderthal man who was considered as the first wise man, was evolved around 1.5 lakh years ago.
  • For around 1 lakh years from then, cranial capacity of man increased.
  • Man also discovered fire.
  • The brain of 50000-year-old man evolved in such a way that, he could be considered as the member of wise man (Homo sapiens)
  • Cro magnon man evolved around 50000 years ago.
  • Now the evolution became faster.
  • 10,000 years ago, Man started practicing agriculture, cattle rearing, establishing cities.
  • Then cultural development started
  • 500 years ago, Art of drawing developed
  • 400 Years ago, Modern Science developed
  • 200 years ago, Industrial society was established.

Heredity and Evolution Notes

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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