Mendelian Genetics

• Gregor Mendel


  • Austrian Monk
  • Physics and Natural History teacher
  • Conducts biological experiments in a small garden
• Pisum Sativum


  Garden pea
• Basic principles of inheritance


  • Reasons for choosing garden peas:
  • Several varieties
  • Self-pollination
• Mendel's Experiment


  1. Pea plants normally self-pollinate

  2. Mendel was able to follow the inheritance of single, easily distinguishable trait
• F1 Generation


  • A hybrid is an offspring of parents with different traits
  • First filial generation
  • P generation or parental (starting breeding plants)
• F2 Generation


  • Second cross (F2 cross) resulted in hybrids in this generation
  • Dominant and recessive traits appeared
  • 3:1 ratio or three plants with dominant traits to one plant with recessive traits
  • Mendel concluded that sex cells or gametes of garden peas contain factors that induced the appearance of a particular trait
• Mendel's Basic Observation


  • Contain at least two genes that were contributed by each parent
• Dominant allele


  Upper case (B)
• Recessive


  Lower case (b)
• Homozygous


  Identical pair of alleles for a trait such as TT (for tall) or tt (for short)
• Heterozygous


  Mixed pair of alleles such as Tt (for short)
• Punnett Square


  Method of tabulation used to predict the possible offspring of a cross between two parents
• Reginald Punnett


  Developed the Punnett Square
• Principle of Paired Unit Factors


  Characters are controlled by hereditary particles called unit factors (come in pairs)
• Mendel's observation


  Traits did not blend, so some invisible factor must determine each of the traits he investigated
• Law of Dominance and Recessiveness


  If an organism inherit different alleles for the same trait, one allele may be dominant over other
• Law of Inheritance

  Process by which certain characteristics such as dominant and recessive traits, are transmitted from one generation to the next
• Law of Segregation


  1. Segregation - alleles separate into different haploid cells that eventually give rise to gametes

  2. Fertilization - male and female gametes randomly combine with each other
• Law of Independent Assortment


  Segregation of the members of any pair of alleles is independent of the segregation of other pair in the formation of reproductive cells
• Alleles


  Different forms of a gene
• Phenotype


  Observable characteristics
• Genotype


  Genetic make up