Part 1

• Before the 1600s, it was believed that life could arise spontaneously

  • wiggly worms in a water barrel
  • maggots arose on rotting meat
• Redi's 1650 experiment protecting meat from flies
• Leeuwenhoek's 1677 compound microscope revealed:

  • "animacules" in pond water
  • motile sperm
• Pasteur 1861 developed sterilization
• There are now over 8 billion people on Earth

  • Except for rare twins, all differ genetically
• There are millions of insect species and differences within species abound
• Holistic attitudes allowed observation but not experimentation since the results would not be "real", leading to concepts from 3 Greek philosophers:

  • Pythogoras
  • Empedocles
  • Aristotle
• Pythagoras 500 BCE "A moist vapor condenses in semen to become an embryo in a uterus"
• Empedocles around 450 BCE suggested the mother also contributes a vapor
• Aristotle 300 BCE said the vapors are collected in the blood

  • Gave rise to the concept of pure blooded animals
• Example of holistic attitude:

  If you take an eye out, it's not working anymore so you can't study it accurately
• Linnaeus 1750s developed criteria for his student to use for identification and classification of species (Genus/species)
• We typically assume members of a species can cross and produce fertile progeny
• Leeuwenhoek's microscope allowed him to see rabbit sperm entering an egg
• Lamark 1790s thought use of parts would shape the particles ex. "long necks in giraffes and swans" gave elongated neck epigenes
• Darwin proposed 1859 that chance changes of the epigenes would give selective reproductive advantages for different environments
• 1831: cell nuclei described
• 1838-40: Schleiden and Schwann realize that cells come from cells
• 1882: Fleming described mitosis
• 1884: Weismann suggested chromosomes behave as expected for carriers of genetic information
• 1876: Kurtwig predicted that sperm and eggs have at least half of the genetic code
• Gregor Mendel

  • Augustin monk; lived 1822-1884
  • interest in plant reproduction
  • experimented with garden peas
  • published in 1865 but not recognzed as significant until 1900
• Gregor Mendel examined individual characters with simple alternatives, kept pedigrees for multiple generations, and kept track of numbers of each type of progeny
• Pisum sativum: garden peas
• Gregor Mendel is the father of genetics
• Peas have a "perfect" flower, with both male and female reproductive organs; the flower is normally closed so that self fertilization automatically occurs
• Crosses are made by removing anthers before pollen is produced and introducing pollen from a different strain (variety)
• Each pea that develops in the pod represents an independent fertilization
• Peas are diploid, thus providing two complete sets of all genes, one from each parent
• diploid: have two sets of chromosomes, one from each parent
• 7 characters Mendel described:

  • flower color
  • flower position
  • seed color
  • seed shape
  • pod shape
  • pod color
  • stem length
• Mendel self pollinated plants displaying each character for several generations to verify they were true breeding before making crosses
• Crosses between true breeding parents for each trait all showed that the F1 progeny in each of the crosses exactly resembled one parent
• In each cross, the F1 progeny all resembled one parent, defining the dominant version of the character, but the alternant phenotype (recessive) made up 1/4 of the progeny in F2 generation from self pollinated F1 plants.
• Since he started with true breeding parents, Mendel concluded that each plant contributed one "factor" to the progeny and introduced the concept of using capital letters for the dominant and the same small letter for the recessive factor (now allele)
• Although he wrote the genotype with the letters above and below each other, it is simpler to list the "monohybrid" crosses
• allele: alternate form of gene
• monohybrid: one gene
• Mendel made all the reciprocal crosses to verify that it did not matter whether the alleles came from the egg of pollen
• Mendel's first law: the law of segregation


  Alleles sort to gametes in a random fashion