CHAPTER 1

• Genetics


  The study of heredity and the variation of inherited characteristics
• Mendel's Principles of Heredity


  Also known as Mendelian Inheritance
• Gregor Johann Mendel (1822-1884) was born in Moravia, Central Europe and was ordained a priest in 1847
• Mendel completed his experiments with peas in 1863 and published the results in 1866
• Mendel's discoveries and the study of heredity were then coined a new term: GENETICS, from the Greek word meaning "to generate"
• Factors that contributed to Mendel's success

  • Choice of suitable organism - the Garden Pea (Pisum sativum)
  • Pea is a dicot, easily grown, highly inbred (self-fertilization), displaying little genetic variation, homogeneous and true-breeding plants
  • Pea has discrete traits, a short generation, an ability to either self- or cross-pollinate and a large number of offspring
  • He restricted his examination to one or very few pairs of contrasting traits in each experiment
  • He kept accurate quantitative records
• Mendel studied seven characters in pea plants
• Characters Mendel studied


  • Flower color
  • Flower position
  • Stem Height
  • Seed color
  • Seed shape
  • Pod shape
  • Pod color
• Each characteristic showed two variants within the same species
• Hybridization


  The mating or crossing between two individuals that have different characteristics
• Hybrids


  The offspring that result from such a mating
• Types of crosses Mendel carried out

  • Self-fertilization
  • Cross-fertilization
• Mendel carried out two types of crosses: self-fertilization and cross-fertilization
• Monohybrid cross


  A cross between parents differing in only one trait or in which only one trait is being considered
• Gene


  A hereditary determinant of a specific biological function, a molecular unit of inheritance (DNA) located in a fixed position
• Allele


  One of a pair, or series, of alternative forms of a gene that occur at a given locus in a chromosome
• Homozygote


  An individual in which the two copies of a gene are the same allele
• Heterozygote


  An organism with unlike members of any given pair or series of alleles that consequently produces unlike gametes
• Genotype


  The allelic constitution of each strain/organism
• Phenotype


  The physical appearance of each strain/organism
• In genetics, the letter that is chosen to denote the alleles of a gene is usually taken from the word that describes the recessive trait (d, for dwarfness)
• Capital letters are used for dominant alleles, and lowercase letters are used for recessive alleles
• Parental strains = P, Progeny = F (F - filial, meaning "son" or "daughter"). F1 = first generation; F2 second generation; F3 third...
• Dwarfness is recessive and tallness is dominant
• Recessive


  A term applied to one member of an allelic pair lacking the ability to manifest itself when the other or dominant member is present
• Dominance


  A condition in which one member of an allele pair is manifested to the exclusion of the other
• Mendel performed other monohybrid crosses with pea plants
• Other monohybrid crosses performed by Mendel

  • Tall plants x dwarf plants
  • Round seeds x wrinkled seeds
  • Yellow seeds x green seeds
  • Violet flowers x white flowers
  • Green pods x yellow pods
• The controlling factors for the recessive and dominant forms are now called genes
• Alternate forms of a gene are called alleles (meaning - "of one another")
• Test cross


  The dominant phenotype cross with recessive phenotype (= recessive genotype) to determine the dominant genotype of parent
• Dihybrid cross


  A cross between two different genes that differ in two observed traits
• Haploid gametes produced by a diploid plant contain one copy of each gene
• Gametes from GG WW plants contain one copy of the seed color gene (G allele) and one copy of the seed texture gene (W allele) or symbolized by G W. Gametes from gg ww plants are written g w.
• Cross-fertilization produces F1 hybrids (Gg Ww), and their yellow, round seeds
• Locus


  A specific location on a chromosome where a gene is located
• Dominant


  A trait that is expressed when the allele is present, even if only one copy is inherited
• Heterozygous


  Having two different alleles for a particular gene
• Crossing two heterozygous individuals

  1. Produce offspring

  2. Determine genotypes

  3. Determine phenotype ratio
• Recessive


  A trait that is only expressed when two copies of the recessive allele are inherited