GENBIO2

• Mendelian Genetics


  The fundamental laws of inheritance discovered by Gregor Mendel through his work on pea plants
• Gregor Mendel


  Father of Genetics
• Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent. Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits.

  
• Mendel's Laws


  • Inherent characteristics and genetic information are carried by discrete units known as genes
  • Genes consist of DNA which are found in chromosomes that segregates independently during the formation of gametes and unite randomly to form an offspring
• Pea plants


  • Have many traits with two distinct forms and no intermediates
  • Are small and abundant
  • Mature quickly
  • Reproduce in large number
  • Mating can be controlled by using either self-fertilization or cross-fertilization
• Mendel grew and tested 28,000 pea plants for 7 years in the garden of the abbey where he had been an abbot
• Pea plant traits or characteristics

  • Height (Tall or Short)
  • Pod Shape (Inflated or Constricted)
  • Pod Color (Green or yellow)
  • Seed Color (Green or Yellow)
  • Seed shape (Round or wrinkled)
  • Flower color (Purple or white)
  • Flower Position (Axial or terminal)

  
• Hybrid


  The offspring of two pure bred parents, with different traits
• Mendel's methods of controlling fertilization

  1. Self-fertilization (Always produces offspring with the same traits as the parent plant)

  2. Cross-fertilization (Produces offspring that may be different or the same as the parent plant)
• Mendel ensured that parental generations are true-breeding by fertilization of contrasting P generation (parental generation) plants, with offspring known as the F1 generation (1st filial generation)
• The F1 generation always showed one of the two contrasting traits, known as dominant traits
• Mendel let the F1 generation self-fertilize to produce the F2 generation. The F2 generation always showed both traits in a 3:1 ratio, in which one offspring exhibit the recessive trait.
• Mendel's 1st Principle (Law of Independent Assortment)


  • Variations in the inherited traits of offspring are attributed to gene variants known as alleles
  • Chromosomes carry genes at every locus where pairs of alleles that hold genes for particular traits are found
  • The similarity and difference between each allele determine which traits will be dominant or recessive
• Mendel's 2nd Principle (Law of Segregation)


  • Every offspring contains two copies of a particular gene, one coming from each parent
  • During the formation of gametes, the pairs of alleles for a specific trait separate from one another and result in gametes that carry only a single inheritable trait
  • When gametes join during fertilization, each of them contributes one allele to an offspring
• Homozygous


  When both alleles in a single pair are similar
• Heterozygous


  When alleles for the same trait are dissimilar
• Homozygous Dominant


  Represented by the same two letters in uppercase form (AA)
• Homozygous Recessive


  Represented by the same two letters in the lowercase form (aa)
• Heterozygous


  Represented by one uppercase form and one lowercase form of the same letter (Aa)
• Genotype


  The complete combination of alleles for a particular gene, the inherited genes, traits, and DNA coding passed from the parental generation to the offspring
• Phenotype


  The observable physical traits inherited by the offspring, such as the yellow or green seed color in Mendel's experiment
• Mendel's 3rd Principle (Law of Dominance)


  • In a cross between two parents that are pure for a particular trait, one allele will be dominant over the other
  • The dominant allele carries the dominant trait which appears in every generation of a heterozygous pairing
• Using a Punnett Square to predict results

  1. Construct a box with four smaller squares inside, then determine the parental genotypes of the crosses

  2. Write the possible gametes from one parent along the top of the square, using the law of segregation

  3. Write the possible gametes of the other parent along the left side of the square, using the same procedure

  4. Combine each allele along the top of the box with each allele along left side, placing them in their respective boxes

  5. Calculate the genotypic and phenotypic ratios of the crosses

  
• The genotypic ratio of the F2 generation in Mendel's monohybrid cross is 1:2:1 (YY:Yy:yy), and the phenotypic ratio is 3:1 (3 yellow seeds and 1 green seed)

  
• The Law of Independent Assortment

  • Mendel observed that in the process of gamete formation, the alleles of particular genes are inherited independently from one another
  • The allele of the genes in one gamete are different from one alleles of the genes in another gamete
• Pedigree


  A family tree that charts the history of traits passed on among several generations of a family, used to trace the passing of an allele from parents to offspring and to detect which members of the family are afflicted with genetic disorders