CHAPTER-10 Heredity and Evolution

  • “The inheritance of characteristics through generation is called heredity.
  • Gregor Johann Mendel (1822 – 1884) worked out the first ever scientificexperimental study on heredity.
  • of garden pea plant
  • Mendel observed in the garden pea plants were
  • Seed shape – Round /Wrinkled
  • Seed colour – Yellow / Green
  • Flower colour – Violet / White
  • Pod shape – Full / Constricted
  • Pod Colour – Green / Yellow
  • Flower position – Axillary / Terrninal
  • Stem height – Tall / Dwarf

Mendel’s monohybrid cross

ratio of 3:1 l

  • The first experiment of Mendel Q e inheritance of a single trait (Height of the plant Tall/ Dwarf)is called Monohybrid Cross.
  • Expression of rnorphological characters as tall or dwarf plant, violet orwhite flower is called Phenotype
  • The expressionof gene(or Chromosomal make up) of an individual for a particular trait is called Genotype

Physical basis of heredity

  • The genes are the factors which form the physical basis for inheritanceof Characters.
  • The alternate expressions of the same gene are called alleles.


  • Variation may be defined as the differences in the characteristics amongthe individuals of the same species (intra specific variation) or among the different genera (intergeneric variation) or different species (Interspecific Varation).
  • No two individuals are identical to each other.
  • Asexual reproduction thus results in off springs with minor variations.

Types of variations

  • Somatic Variation – It pertains to body cells and it is not inherited.
  • We often associate Darwin solely with the theory of evolution.
  • Germinal Variation – It pertains to germ cells or gametes and it is inheritable. It leads to speciation and evolution.

Significance of Variation

  • It is the source of raw material for evolution.
  • Animals are able to adapt themselves to the changing environment
  • Organisms are better suited to face the struggle for existence
  • Variations give the organisms an individually of their own.
  • Jean Bapdse Lamarck (1744-1829) postulated the Use and Disuse Theory.
  • Lamarck quotes the example of development of long neck of Giraffe.

Theory of Natural Selection

  • Charles Darwin put forth the law of natural selection involving struggle for existence and survival o the fittest.


  • Av Evolution may be defined as a gradual development of more complex species from pre-existing simple forms.


  • Thus speciation is arising of a new species from a sub-population of a species which is geographically or reproductively isolated over a long period of time from the other population of the same species.

Human Evolution

  • First human like being – the hominid. The hominid was called Homohabilis.
  • 5 million years ago with the rise of Homo erectus who were meateaters.
  • The Neanderthal man who lived in East and Central Asia 1 million years ago.
  • Archaic Homo sapiens arose in South Africa
  • Between 75,000- 10,000 years, the modern Homo sapiens arose

Evolution Tree

  • Show the inferred evolution, relationships among various biologicalspecies or other entities based upon similarities and differences in theirphysical and genetical characters

Genetic Engineering

  • Genetic engineering is the modification of the genetic information of living organisms by manipulation of  DNA by adding, removing or  repairing   part of genetic material(DNA) and changing the phenotype  ofthe organism
  • It is also known as gene manipulation or recombinant DNA Technology(r-DNA Technology).
  • The benefits derived through the Genetic Engineering include:
  • Understanding of the gene structure and function through basic research.
  • Production of large quantities of insulin, interferon (Anti-Viral Proteinproduced by Virus infected cells) human growth hormone, proteins (Polypeptides) and vaccines for foot and mouth disease of cattle (komari – in Tamil) etc.,
  • This technique is also employed in the transfer of genes involved in Nitrogen fixation (NF – genes).

Basic techniques in Genetic Engineering

  • Restriction enzymes or Restriction endonucleases are molecular scissorswhich cut DNA at specific sites.
  • DNA ligases are the paste enzyme which helps to join the broken DNA fragments.
  • Bio-Technology and Cloning
  • There are several applications of Bio-technology such as brewing,industry, enzyme technology, manufacturing of anti-biotics, organicacids, vitamins, vaccines, steroids and monoclonal anti -bodies.
  • It was Edward Jenner (1749-1823) in 1791 who coined the term vaccine
  • Brewing Industry: Fermentatiuon in alcoholic  beverages like beer, wine.
  • Enzyme Technology:Enzymes are bio-catalysts that speed up reaction in cells.
  • Many enzymes are utilized in the Pharmaceutical industry.
  • Anti – Biotics:
  • Organic Acids:Acetic acid is used for the production of vinegar

Development of Dolly

  • Dolly was a cloned sheep, developed by Dr. lan Wilmut and hiscolleagues in Roselind Institute in Scotland in July 1996.

Vitamins: These are chemical compounds present in variable minutequantities in natural food stuffs.

  • They do not furnish energy but are very essential for energy transformation and regulation of metabolism.
  • Vaccines: Vaccines are substances that confer immunity against specificdisease. They act as antigens and stimulate the body to manufactureantibod.

Steroids: They are a type of derived lipids Ex: Cholesterol, containingsteroid drugs like prednisolone is produced from fungus Rhizopus.

Monoclonal anti-bodies: These are the anti bodies by cloned cells.Monoclonal anti – bodies, are now used for treatment of cancer.


  • Cloning is an experimental technique wherein a group ofmorphologically and genetically identical organisms are produced.
  • A clone may be defined as an exact carbon copies of a single parent.

Types of clones

  • Natural clones: the natural clones include identical twins
  • Induced clones:

Stem Cell(Organ)Culture

  • Unspecialized calls which have the potentiality of growing and multiplying into enormous number  of same type of cells by repeated
  • They can be introduced to become any other type of tissues with specific functions i.e

Types of Stem Cells

Embryonic Stem Cells: The embryonic stem cells can be derived fromearly embryo which is developed by “invitro fertilization” (fertilizationbe made artificially in the laboratory).

Adult or Somatic Stem Cells: They can grow, multiply and can bedifferentiated into same type of tissues into which they are implanted. The mechanism of adult or Somatic stem.

  • The somatic stem cells are derived from sources such as bone marrow, embryos, amniotic fluid and umbilical cord.

Microbial Production

Vaccines: Killed or live germs suspension which is employed to induce the production of antibodies and bring forth immunity.

Antibiotics: Antibiotics are chemical substances derived from microbes like fungi, bacteria etc., employed to kill the infectious germs and cure a disease.

Vitamin B12 : Bio technologically synthesized vitamin B12 is used, to  cure pernicious anaemia.

Enzymes: Amylase is derived from amyloproteins of bacteria.

Insulin: Diabetes is treated by the biotechnologically produced insulin

Bio-Sensor and Bio-Chips

Bio sensor: It is a device consisting of immobilized layer of biological material such as  enzyme, antibody, hormone , nucleic acids, organelles or whole cells and its contact with a sensor


  • Biological Computers will be developed using bio-chips.Bio-chips will be useful in defense ,medicine ,etc.,

Gene Therapy

  • Insulin dependent diabetes is neared with insulin injection.Insulin dependent diabetes is causedby the degeneration of beta cells due to a defective gene.
  • Applying the principle of Bio-technology, it is possible to correct the defective gene. When the defective gene is corrected with a new genethe genetic defect developed is, rectified and cured. It can be used to treat defects in Somatic i.e (body) or Gametic (sperm or eggs) Cell.

Types of Gene Therapy

Somatic gene therapy- The genome (gene set) of the recipient ischanged.

Germ line gene therapy- Egg and sperm of the parents are changed,for the purpose of passing the changes to the next generation

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