bio

• Pedigree


  A genetic diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships
• Pedigrees


  • Make it easier to visualize relationships within families, particularly large extended families
  • Are often used to determine the mode of inheritance (dominant or recessive) of genetic diseases
• Recessive pedigree


  • Unaffected parents can have affected offsprings
  • Affected off springs are both male and female
  • The trait can skip generations
• Tips for recessive trait pedigree analysis

  1. For an individual to be affected (homozygous), both parents need to be carriers (heterozygous)

  2. To calculate the chance that an unknown individual will be affected, calculate the chances that the parents will be heterozygous

  3. For rare traits make the simplifying assumption that unrelated, unaffected individuals are not carriers
• Dominant pedigree


  • Affected individuals have at least one affected parent
  • The phenotype generally appears every generation
  • Two unaffected parents only have unaffected off springs
• Mutation


  A sudden change in a gene or a whole chromosome that will be passed on to new cells by mitosis, or to new individuals by meiosis
• Mutation


  • Has a harmful effect on the cell in which it occurs
  • A mutation in a gamete affects all the cells of the individual which develops from it
  • A mutation in a somatic cell (body cell) will affect only those cells produced by mitosis from the affected cell
• Types of mutation


  • Gene mutation or point mutation
  • Chromosomal mutation
• Gene mutation (point mutation)

  1. A change in base sequence of the DNA molecule in a particular region of the chromosome

  2. This change is transcribed to mRNA and results into a wrong protein formation during translation
• Types of gene mutation

  • Duplication: a nucleotide is inserted twice instead of once
  • Deletion: a nucleotide is missed out
  • Substitution: A different nucleotide is used in place of the normal
  • Inversion: the sequence of the bases in a triplet is reversed
• Chromosomal mutation


  • Down's syndrome (trisomy)
  • Klinfelter's syndrome (trisomy)
  • Turner's syndrome (monosomy)
• Mutagens


  • Ionizing radiations like UV light, X-rays and gamma rays
  • Chemicals eg. Mustard gas and nitrous oxide
  • Cigarette smoke chemicals and tar
• If a mutation results in cancer, the mutagens responsible are known as carcinogens
• Most mutations are harmful or even fatal to an organism
• Some mutations are 'neutral' and if they arise in the gametes may be passed on without affecting the survival of the off springs
• A few mutations can be beneficial and give a selective advantage to the individual help the organism survive in unfavorable environmental conditions
• Evolution


  Change over time caused by natural selection which is caused by a change in the environment and leads to formation of a new species from an original species