11.1 - Mendelian Genetics

• Genetics: the study of heredity - how traits get passed from one generation to the next

  • ex: eye color, blood type, skin color
• Gregor Mendel - An Austrian monk (mid 1800's) who was a gardener. Pioneer in studying genetic inheritance which is a huge component in biology.
• Mendel's Experiments

  • Key terms:
  • self-pollination: pollen (sperm) from a plant fertilize its own eggs. The resulting seeds are all identical to themselves.
  • same plant!
  • cross-pollination: pollen from one plant fertilizes the eggs of another plant
  • two plants
• Mendel's Experiments

  • Mendel called:
  • P = original parent generation (your parents)
  • F1 = 1st generation offspring (you)
  • F1 offispring of parents with different traits are called hybrids
  • F2 = 2nd generation offpring (your kids)
  • When Mendel crossed plants, the F1 looked like only 1 parent, not a blend of the two traits!
• Mendel's Conclusions:

  • Inheritance and Dominance
  • Inheritances is determined by "factors" called genes, which are small portions of DNA that code for proteins
  • The proteins then control how a trait is expressed
  • Each trait Mendel studied was controlled by two genes that come in contrasting forms
  • Ex: the gene for "plant height" comes in two forms - tall & short
  • the two forms of a gene are called alleles
• Mendel's Conclusions:

  • Inheritance and Dominance
  • Principle of Dominance
  • Some alleles are dominant and some are recessive
  • An organism that has a dominant allele for a trait will always express the dominant form
  • An organism that has a recessive allele for a trait will only show the recessive form of the trait when the dominant allele is not present
  • A dominant allele can mask or hide a recessive allele - Mendel noticed that the recessive form seemed to disappear in the F1 generation and reappear in the F2 generation
• Mendel's Conclusions:

  • Law of Segregation
  • The pair of genes for a trait separate from one another in meiosis.
  • When Mendel crossed his F1 plants, the recessive form of the trait showed up in the F2
  • Ex: a parent plant who is Tt can pass an T or t to the offspring via the egg
  • The result of this process is an F2 generation with new combinations of alleles