Introduction to Genetics

• Gregor Mendel is born into a peasant family in Hyncice, Czech Republic


  1822
• Mendel enters St. Thomas, a Roman Catholic monastery, where he studies theology, philosophy, and science


  1843
• Mendel is sent to the University of Vienna to study to become a science teacher

  1851
• Mendel conducts carefully designed experiments with nearly 30,000 pea plants in the monastery garden


  1856-1863
• Mendel publishes his work, "Versuche über Pflanzen-Hybriden" (Experiments on Plant Hybridization), detailing his experiments and findings


  1866
• Mendel serves as the abbot of the monastery, continuing his botanical studies and research until his death


  1868-1884
• Pea plants


  • Distinct, identifiable characteristics
  • Suitable for controlled experiments
• Mendel confirmed the concept of purebred plants and their consistent transmission of traits from one generation to the next
• Mendel's Laws of Heredity

  Principles of segregation, independent assortment, and dominance in heredity
• Genes


  Hereditary factors that exist in pairs within an organism
• Alleles


  Different versions of the same gene, located on homologous chromosomes
• Dominant allele


  Masks the expression of the recessive allele in a heterozygous state
• Recessive allele


  Only appears in the phenotype when both alleles are recessive
• Segregation


  During gamete formation, the paired alleles for a specific trait separate randomly, and each gamete receives only one allele from the pair
• Mendel's work was virtually ignored by the scientific community in the 1860s-1880s, overshadowed by debates on Darwin's theory of evolution
• In the early 20th century, Mendel's work was resurrected, and he was acknowledged as the father of genetics, with his ideas becoming foundational to the understanding of heredity
• Important genetic terms


  • Gene
  • Allele
  • Locus
  • Genotype
  • Heterozygote
  • Homozygote
  • Phenotype or trait
  • Characteristic or character
• Creating Punnett Squares


  1. Determine parental genotypes

  2. Separate alleles

  3. Set up the grid

  4. Label the axes

  5. Fill out the squares representing fertilization
• Monohybrid cross


  A cross involving one pair of contrasting traits
• Dihybrid cross


  A cross involving two pairs of contrasting traits
• Genotypic ratio is the ratio of different genotypes in the offspring
• Phenotypic ratio is the ratio of different phenotypes in the offspring