1. Cytology
    2. 1. Tools used in Cytology
    2. Cell Biology
    3. Cell cycle
    4. Biomolecules
  2. Genetics
    3. 5. Introduction
    6. Inheritance
    7. Mutation and Polypoidy
  3. Plant Anatomy
    4. 8. Plant Anatomy
    9.
  4. Plant Physiology
    5. 10. Respiration
    11. Photosynthesis
    12. Growth and Growth hormone
    13. Mode of nutrition and Habitat in Plants
  5. Classification and Biodiversity
    6. 14. Classification
    15. Virus
    16. Bacteria
    17. Thallophyta
    18. Bryophyta
    19. Pteridophyta
    20. Gymnosperm
    21. Reproduction
    22. Morphology of Angiosperm
  6. Taxonomy, Ecology and Application of biology
    7. 23. Taxonomy
    24. Ecology
    25. Application of Biology
Genetics
7. Mutation and Polypoidy
INTRODUCTION
▢ Genetics:
❖ Topic: Mutation and Polyploidy
❖ Definition: Mutation is a sudden change in phenotype due to a change in the genome of a cell or virus.
❖ Discoverer:
◉ Name: Hugo de Vries
◉ Contributions:
  1. Discovered mutation in Oenothera lamarckiana (Evening primrose)
  2. Coined the term 'Mutation'
  3. Defined mutation as 'Sudden phenotypic changes which are heritable'
    4. ■ Note: Later discovered that mutation in Oenothera lamarckiana was due to polyploidy.
❖ Scientific Study: Given by Morgan
❖ Causes:
◉ Radiations:
◈ Gamma-rays: Produce free radicals
◈ X-rays: Cause deletion
◈ UV-rays: Cause dimer formation
◉ Mutation Effects:
  1. 99.9% mutations are harmful (lethal)
  2. Most common mutations: lethal, followed by recessive
1. The most common type of mutation is
  • Lethal
  • Recessive
  • Dominant
  • Addition
2. Which of the following is correct about mutation?
  • 99.9% mutations are harmful
  • 1 in 1000 mutation is beneficial
  • Mutation in somatic cell is heritable
  • Both a and b
❖ Stages of Occurrence:
  1. Before formation of gamete
  2. In gamete
  3. In zygote
❖ Importance:
  1. Useful in crop variety development
  2. UV-treated Penicillium strains yield high penicillin
  3. Phenotypic changes due to gene mutation are reversible; due to chromosomal changes are irreversible
  4. Allelic variations arise from mutation
  5. Ultimate cause of variation is mutation; major cause is sexual reproduction
  6. Basic cause of evolution
❖ Types:
  1. Natural
  2. Induced (via mutagens)
❖ Mutagens:
◉ Definition: Agents that cause mutations
◉ Types:
◈ Physical:
  1. Temperature
  2. Radiations
    3. ● Ionizing:
    1. X-rays
    2. γ-rays
    ● Non-ionizing:
    1. UV-rays
◈ Chemical:
  1. Mustard gas
  2. Acridine dye
  3. Colchicine
  4. Nitric oxide (NO)
  5. Maleic hydrazide
  6. Hydroxylamine
  7. Ethyl methane sulfonate (EMS)
◉ Notable Facts:
  1. H. J. Muller first induced mutation in Drosophila using X-rays
  2. H. J. Muller is called father of Actinobiology
  3. X-rays, β-rays used for deep-seated nucleus tissues; UV-rays for superficial ones
  4. First chemical mutagen made by C. Auerbach
❖ Mutation Rate: Natural mutation frequency is very low (1×10⁻⁵ to 1×10⁻⁶)
❖ Types of Mutation:
◉ Forward: Wild type changes to new type
◉ Reverse: Mutant type changes back to wild
❖ Study Material:
◉ Best: Haploids
◉ Model Organisms:
  1. Drosophila (2n = 8)
  2. Neurospora (haploid; called Drosophila of plant kingdom, pink mould)
  3. E. coli
  4. Bacteriophage
◉ Discoveries:
  1. Beadle and Tatum discovered 'One gene one enzyme hypothesis' in Neurospora (Nobel Prize 1958)
  2. Yanofsky: 'One gene one polypeptide' theory
TYPES OF MUTATION
▢ Gene Mutation / Point Mutation:
❖ Frame Shift Mutation:
◉ Description: Occurs due to insertion or deletion at initial/internal position; affects all downstream codons.
◉ Effect: Most dangerous mutation type.
◉ Examples:
  1. Deletion
  2. Addition/Insertion
❖ Substitution Mutation:
◉ Transition: Purine↔Purine or Pyrimidine↔Pyrimidine
◉ Transversion: Purine↔Pyrimidine
◉ Example: Sickle cell anemia caused by transversion
▢ Chromosomal Mutation:
❖ Structural Changes:
◉ Deletion: Loss of chromosome part
◉ Inversion: Reinsertion in reverse order (180° twist)
◉ Duplication: Part joins homologous chromosome
◉ Translocation: Part joins non-homologous chromosome
❖ Numerical Changes:
◉ Aneuploidy:
◈ Definition: Change in individual chromosome number
◈ Types:
■ Hypoaneuploidy:
● Nullisomic (2n–2): Loss of chromosome pair (non-survivable)
● Double monosomic (2n–1–1): Loss of 2 dissimilar chromosomes
● Monosomic (2n–1): Loss of one chromosome; causes Turner's syndrome (44+XO)
1. If 2n = 14, how many monosomics are possible?
  • 14
  • 7
  • 28
  • 21
■ Hyperaneuploidy:
● Trisomy (2n+1):
  1. Patau syndrome (Trisomy 13)
  2. Edward's syndrome (Trisomy 18)
  3. Down's syndrome (Trisomy 21)
● Sex Chromosomal Trisomies:
  1. Super female (XXX)
  2. Klinefelter's (XXY)
  3. Super male (XYY)
  4. Double trisomy (2n+1+1)
● Tetrasomy (2n+2): e.g., Super female (XXXX)
◉ Euploidy:
◈ Definition: Change in entire haploid set
◈ Types:
■ Homoploidy: n
■ Polyploidy:
● Autopolyploidy:
⟣ Definition: Multiple sets from same genome
⟣ Examples:
➢ Autotriploid (AAA):
  1. Banana
  2. Grapes
  3. Doob grass
➢ Autotetraploid (AAAA):
  1. Barseem
⟣ Note: Autotriploids are always sterile
● Allopolyploidy:
⟣ Definition: Sets from different species
⟣ Examples:
➢ Allotetraploid (AAA'A'): Raphano brassica
➢ Allohexaploid (AAA'A'A"A"): Triticum spelta (Wheat)
● Autoallopolyploidy: e.g., AAAAA'A' / AAABBB
◈ Special Notes:
  1. Triticale is the first man-made cereal crop
  2. Autopolyploids form multivalents during synapsis
  3. Allopolyploids form bivalents