Topics to be learn :

  • Heredity and Hereditary Changes,
  • Transcription, Translation & Translocation
  • Evolution
  • Evidences of Evolution
  • Darwin’s Theory of Natural Selection
  • Lamarckism
  • Speciation
  • Human Evolution

Inheritance or Heredity:

  • Process of transfer of physical and mental characters from parents to offspring.
  • Chromosomes in the nucleus carry hereditary traits.

Components of the DNA Molecule: Two helical strands with deoxyribose sugar, phosphoric acid, and pairs of nitrogenous bases.

Heredity and Hereditary Changes:

  • Heredity: Transfer of biological characters from one generation to the next via genes.
  • Hereditary Changes: Alterations in inherited traits across generations.

History of Genetics:

  • Gregor Johann Mendel (1886): Conducted pea plant experiments explaining inheritance.
  • Hugo de Vries (1901): Proposed Mutational Theory for sudden changes.
  • Walter and Sutton (1902): Discovered paired chromosomes' role in inheritance.
  • Oswald Avery, Mclyn McCarthy, and Colin MacLeod (1944): Identified DNA as genetic material in organisms.
  • Francois Jacob and Jack Monad (1961):
    • Developed protein synthesis model using DNA.
    • Led to understanding genetic codes and genetic engineering.

Emergence of Genetic Engineering:

  • Understanding DNA led to genetic engineering.
  • Emergence of recombinant DNA Technology.

 Benefits of Heredity Science:

  • Diagnosis of Hereditary Disorders: Identifying genetic diseases.
  • Treatment of Incurable Disorders: Developing therapies for hereditary illnesses.
  • Prevention of Hereditary Disorders: Implementing measures to avoid genetic diseases.
  • Production of Hybrid Varieties: Creating new animal and plant breeds.
  • Industrial Processes with Microbes: Utilizing microbes in various industrial applications.

DNA:
  • Double helix structure composed of two strands.
  • Each strand consists of nucleotides: phosphoric acid, deoxyribose sugar, and nitrogenous bases.
  • Two types of nitrogenous bases: purines (adenine, guanine) and pyrimidines (cytosine, thymine).
  • Adenine pairs with thymine via double hydrogen bonds; cytosine pairs with guanine via triple hydrogen bonds.
  • Hydrogen bonds maintain the helices' structure.
  •  

RNA:

  • Single-stranded nucleic acid composed of ribonucleotides.
  • Ribonucleotide consists of ribose sugar, phosphate molecules, and nitrogenous bases.
  • Four nitrogenous bases: adenine, guanine, cytosine, and uracil.
  • Found in nucleus and cytoplasm.
  • Three main types of RNA:
    • mRNA (Messenger RNA): Carries genetic information from DNA in the nucleus to ribosomes in the cytoplasm for protein synthesis.
    •  
    • rRNA (Ribosomal RNA): Component of ribosomes involved in protein synthesis.
    •  
    • tRNA (Transfer RNA): Carries specific amino acids to ribosomes based on mRNA instructions for protein synthesis.
    •  

 Genetic Disorders:

  • Causes:

    • Abnormalities in chromosomes and gene mutations.
    • Causes include numerical changes, deletions, translocations, and mutations in genes.

  • Examples:

    • Numerical Changes in Chromosomes:

      • Down's Syndrome: Extra copy of chromosome 21.
      • Turner's Syndrome: Missing or incomplete X chromosome in females.
      • Klinefelter's Syndrome: Extra X chromosome in males.

    • Monogenic Disorders (Mutations):

      • Huntington's Disease, Tay-Sachs Disease, Galactosemia, Phenylketonuria, Sickle Cell Anemia, Cystic Fibrosis, Albinism, Hemophilia, Night Blindness, etc.

    • Polygenic Disorders:

      • Cleft Lip, Cleft Palate, Constricted Stomach, Spina Bifida, Diabetes, Hypertension, Heart Disorders, Asthma, Obesity, etc.

 Transcription, Translation and Translocation :

(i) Transcription:

  • Synthesis of mRNA from DNA.
  • Genes on DNA control cell structure and function.
  • Central Dogma: DNA Transcription → RNA Translation → Protein.
  • mRNA produced from DNA sequence.
  • Only one DNA strand used.
  • mRNA has uracil instead of thymine.
  • Produces complementary mRNA.

 

 

Triplet Codon:

  • Code for each amino acid, consisting of three nucleotides.
  • mRNA carries coded message from DNA to cytoplasm.
  • Dr. Har Govind Khorana discovered triplet codons for 20 amino acids, awarded Nobel Prize in 1968.
  • Each mRNA molecule contains thousands of triplet codons.
  • tRNA supplies amino acids based on mRNA message.

Translation:

  • tRNA with complementary anticodon brought near mRNA.
  • Formation of peptide bonds joins amino acids together.
  • Polypeptide chains come together to form complex proteins.
  •  

Translocation:

  • Ribosome moves along mRNA by one triplet codon distance.
  • Essential for protein synthesis and controlling body functions.

Mutation:

  • Sudden change in genetic material.
  • Causes changes in offspring's characteristics.
  • Two types: minor and major.
  • Contributes to evolution and supports Darwin's theory of natural selection.
  •  

 Evolution:

  • Gradual change in living organisms over a long duration.
  • Results in the development of new species.
  • Natural selection drives continuous changes in specific characteristics.

Phases of Evolution:

  1. Simple elements
  2. Organic and inorganic compounds
  3. Complex organic compounds (proteins, nucleic acids)
  4. Mixture of organic and inorganic compounds
  5. First primitive cells
  6. Development of processes to uptake surrounding chemicals, leading to cell growth
  7. First living organisms; survival based on adaptation to surroundings

Diversity in Living Organisms:

  • Animals: From unicellular amoeba to giant whales and humans.
  • Plants: From unicellular Chlorella to huge banyan trees.
  • Existence of life on Earth: From equator to poles, in air, water, land, and rock.

Theory of Gradual Development: Widely accepted theory worldwide.

Theory of Evolution:
  • Protoplasm, the first living material, formed in the ocean.
  • Unicellular organisms emerged, evolving into larger, more complex organisms.
  • Evolutionary changes occurred slowly over approximately 300 crore years.
  • Different types of organisms developed through multi-dimensional changes, termed organizational and progressive evolution.

Evidences of Evolution: (i) Morphological Evidences:

  • Similarities in external features suggest common ancestry.
  • Examples: Structures like mouth, nostrils, ear pinnae, eye position in animals; leaf shape, venation, petiole in plants.

 (ii) Anatomical Evidences:

  • Structures like human hand, cat's foreleg, whale flipper, and bat patagium exhibit differences in appearance and function.
  • Despite functional differences, similarities exist in bone structure and joints, indicating a common ancestry.
  •  

Organs:

  • Thoracic Cavity: Contains lungs and heart.
  • Skull: Houses the brain.
  • Abdominal Cavity: Contains stomach, intestine, liver, kidney, etc.

Functions:

  • Each vital organ serves a specific function essential for survival.
  • Brain coordinates activities, heart circulates blood, lungs aid respiration, kidneys filter waste.

(iii) Vestigial Organs:

  • Degenerated or underdeveloped organs lacking function.
  • Result from evolutionary changes and natural selection.
  • Examples: Appendix, tail bone (coccyx), ear pinna muscles, wisdom teeth, body hairs.

 (iv) Paleontological Evidences:

Fossil:

  • Remains or impressions of organisms preserved in the earth's surface.
  • Formed by natural calamities burying organisms.
  • Provide direct evidence of evolution.

Carbon Dating:

  • Technique to determine fossil age.
  • Living organisms absorb carbon, but it stops after death.
  • C-14 in organisms decays over time.
  • Age determined by time since death, C-14 radioactivity, and C-14 to C-12 ratio.

Uses of Carbon Dating:

  • Study of paleontology and anthropology.
  • Dating human fossils and manuscripts.
  • Placing fossils in the geological time scale.
  • Understanding the evolution of organisms.

Willard Libby:

  • Developed carbon dating method based on C-14 decay.
  • Awarded Nobel Prize in 1960.
  • 'Radio Carbon' journal publishes data on material ages.

 (v) Connecting Links:

(i) Peripatus:

  • Characteristics of Annelida and Arthropoda.
  • Annelid: Segmented body, thin cuticle, parapodia-like organs.
  • Arthropod: Tracheal respiration, open circulatory system.

(ii) Duck-billed Platypus:

  • Characteristics of Reptiles and Mammals.
  • Reptilian: Egg-laying, scales on body.
  • Mammalian: Presence of mammary glands, hair.

(iii) Lungfish:

  • Characteristics of Fishes and Amphibians.
  • Fish: Fish-like body.
  • Amphibian: Respiration with lungs.

These connecting links suggest the evolution from annelids to arthropods, fish to amphibians, and reptiles to mammals.

(vi) Embryological Evidences:

  • Vertebrate embryos show initial similarities.
  • Similarities disappear in later development.
  • Suggest a common origin for vertebrates.
  •   

Darwin's Theory of Natural Selection:
  • Proposed by Charles Darwin (1809-1882).
  • Theory: "Survival of the fittest" - organisms fit for survival evolve, while unfit organisms perish, leading to the production of new species.
  • Presented in the book "Origin of Species."
  • Darwin collected and observed numerous specimens of plants and animals for his study.

Explanation of Natural Selection:

  • Prolific Reproduction: Organisms reproduce abundantly.
  • Competition: There's a struggle for survival among organisms.
  • Essential Modifications: Organisms with beneficial adaptations survive, while others perish.
  • Survival of the Fittest: Natural selection ensures the survival of well-adapted organisms.
  • Reproduction: Well-adapted organisms reproduce more, leading to the emergence of new species with specific traits.

Objections to Darwin's Theory:

  • Other factors besides natural selection may contribute to evolution.
  • Darwin did not explain useful and useless modifications.
  • He did not address the causes of slow and abrupt changes.
    Lamarckism:
  • Jean-Baptiste Lamarck (1744-1829): Proposed Lamarckism, emphasizing the principle of "use or disuse of organs" and the "inheritance of acquired characters."

Key Concepts:

  • Organism Evolution: Every organism strives to evolve.
  • Acquired Characters: Organisms acquire traits during their lifetime through adaptations and modifications.
  • Inheritance: These acquired traits are passed on to the next generation.

Examples:

  • Giraffes developed long necks by stretching to browse leaves.
  • Blacksmiths' strong shoulders due to repeated hammering.
  • Flightless birds have weak wings from disuse.
  • Aquatic birds' hind limbs evolved for swimming.
  • Snakes lost limbs due to burrowing habits.

Objections:

  • Unused organs degenerate and used ones evolve, but inheritance of acquired characters is disputed.
  • Modifications are not inherited by the next generation.
  • Ancestry of acquired characters suggests that organisms can transfer acquired traits to offspring, a concept not widely accepted.

Speciation:

  • Species: Group of organisms capable of producing fertile offspring through natural reproduction.

Key Points:

  • Definition: Formation of new species from earlier ones.
  • Distinct Characters: Each species possesses specific traits.
  • Differences: Species vary in geographical conditions, habitat, reproductive ability, etc.

Factors Affecting Speciation:

  • Genetic Variation: Diversity in genetic makeup.
  • Geographical Changes: Alterations in habitat or environment.
  • Reproductive Changes: Modifications in mating behavior or reproductive organs.
  • Isolation: Geographical or reproductive isolation over an extended period.

Speciation results in the emergence of biodiversity, contributing to the variety of life forms on Earth.

 Human Evolution:

  • Evolutionary History of Modern Man:

    • About 70 million years ago, the ice age began, leading to the extinction of dinosaurs and the rise of mammals.
    • Ancestors of humans evolved from lemur-like animals, followed by monkey-like creatures about 70 million years ago.
    • Approximately 40 million years ago, ape-like animals emerged, with gradual disappearance of tails, body enlargement, and improved brain volume and hands.
    • Two lines of evolution emerged: apes like gibbons and orangutans in Asia, and gorillas and chimpanzees in Africa.
    • Another line led to human-like animals around 20 million years ago.
    • Dry climate led arboreal apes to descend on land, resulting in changes in lumbar bones and hands becoming more manipulative.
    • Hominoid species journey began around 20 million years ago.
    • The first human-like animal recorded was the 'Ramapithecus' ape from East Africa.
    • Ramapithecus → Australopithecus → Neanderthal man → Cro-Magnon are significant steps in human evolution.
    • Neanderthal man was considered the first wise man, with increasing brain growth leading to intelligence.
    • Cultural evolution, including agriculture and civilization development, played a significant role.
    • Industrial inventions about 200 years ago marked human dominance on Earth.

  • Stages of Human Evolution and Time:

    1. Ancient animals like lemurs - 70 million years ago
    2. Egyptopithecus - 40 million years ago
    3. Dryopithecus - 25 million years ago
    4. Ramapithecus - 10 million years ago
    5. Australopithecus - 4 million years ago
    6. Skilled Human - 2 million years ago
    7. Man with erect posture - 1.5 million years ago
    8. Neanderthal - 150,000 years ago
    9. Cro-Magnon man - 50,000 years ago

This evolutionary journey showcases the development of modern humans from ancient ancestors over millions of years.