GENERAL BIOLOGY 2

• Branches of Genetics

  • Molecular Genetics
  • Cytogenetics
  • Transmission Genetics
  • Population Genetics
• Molecular Genetics


  Deals with DNA and gene expression and regulation
• Cytogenetics


  Deals with chromosome structure and behavior during cell division
• Transmission Genetics

  Deals with different patterns of inheritance
• Population Genetics


  Deals with how forces of evolution influence genes in populations
• Gregor Mendel


  • Farm Tender
  • Beekeeper
  • Academician
  • Augustinian Monk
  • Father of Genetics
• Mendel took the path to priesthood when he entered Augustinian monastery of St. Thomas and became monk. This is also where he performed his pea plant studies.
• Garden peas


  • Exhibit vigorous growth
  • Can self-fertilize
  • Can cross-fertilize
• Challenges Faced by Mendel

  • Pangenesis - was the belief that seeds are produced in different organs and will later on gather to form the offspring
  • Homunculus Theory - The invention of the microscope made people believe that sperm cells bear a homunculus or little man
  • Blending Theory - states that traits of parents blend every generation of offspring
• The Experiments on Plant Hybridization was rediscovered independently by de Vries, Correns, and von Tschermak in 1900s.
• Researchers who rediscovered Mendel's work


  • Hugo de Vries
  • Carl Correns
  • Erich von Tschermak
• Chromosome


  Consists of a DNA molecule, which serve as the repository of genetic information in cells
• Homologous chromosomes

  Chromosomes occur in pairs
• Paternal

  From the father or male parent
• Maternal


  From the mother or female parent
• Gene


  The basic unit of heredity. It controls the expression of a biological characteristic
• Characteristic


  A heritable feature of an organism
• Alleles


  The alternative forms of a gene
• Phenotypes


  Refer to the actual manifestation of genotypes into observable traits
• Genotype


  Refers to the set of alleles possessed by an organism
• Homozygous

  Alleles are identical
• Heterozygous

  Alleles are different
• Monohybrid cross


  A mating between two individuals involving one characteristic or one pair of contrasting traits
• Principle of Dominance


  In a heterozygous individual, one allele (dominant) completely masks the expression of the other allele (recessive)
• Law of Segregation


  The two alleles of a gene in an individual segregate or separate from each other during gamete formation
• Dihybrid cross


  A mating between two individuals involving two characteristics or two pairs of contrasting traits
• Law of Independent Assortment


  The alleles from different genes are sorted into the gametes independently of each other. Thus, the inheritance of these two genes become independent
• Testcross


  Determines genotype of the individual with the dominant trait and generates two possible outcomes in the crosses
• Punnett Square


  A simple method where the alleles of parents are combined to determine the possible outcomes of fertilization
• Fork-Line Method


  Requires analysis of each monohybrid cross, can determine offspring ratios directly, no need to identify the alleles
• Probability Methods


  Probability as the mathematical measure of chance, no need to determine the complete offspring ratios
• Product Rule


  The chance of two or more independent events to occur together is equal to the product of their individual probabilities
• Sum Rule


  The probability of either of two mutually exclusive events occurring is equal to the sum of their individual probabilities
• Studying Inheritance in Peas

  • Matings of individuals can be controlled, the generation time is relatively shorter, the number of offspring is relatively larger
• Studying Inheritance In Humans

  • Matings can never be done in controlled conditions, the generation time is relatively longer, the number of offspring is relatively smaller
• Pedigree


  A pictorial representation of how a trait is transmitted among the members of a family
• Pedigree Symbols

  • Male & Female - Use a "square" for male, "circle" for female
  • Unknown Sex - Use a "diamond"
  • Affected Male & Female - Use a "shaded" symbol
  • Deceased - Use a "slash"
  • Proband - Use an "arrow"
  • Carrier - Use a "half-shaded" symbol
  • Mating - Use a "horizontal line"
  • Consanguineous Mating - Use a "double horizontal line"
  • Identical Twins - Use a "common branching point"
  • Fraternal Twins - Do not connect if dizygotic
• Autosomal Dominant Inheritance


  Relatively easier to identify, affected individuals manifest the corresponding trait, have at least one affected parent, tendency to not skip generations
• Autosomal Recessive Inheritance


  Analysis is relatively more challenging, individuals may have the allele but do not express them (i.e., carriers), have both unaffected parents, tendency to skip generations
• Recombination increases genetic diversity. This is the reason why you and your sibling look different even if your genes are inherited from the same parents.