Gregor Mendel

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Gregor Mendels Genetics
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Who is Mendel?

• Hereditary information is passed on to different
  generations through genes
• Genes might not be expressed for several
  generations, but are still passed on, and may
  appear several generations later
• Gregor Mendel was the first scientist to explain
  inheritance
• Mendel did a lot of work with pea plants and
  observed their traits throughout generations

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Mendels Pea Plant Traits
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Mendels Experiment

• Characteristics or traits that can be seen are
  called phenotypes
• Plants that produced seeds, which grew to be the
  exact same phenotypes as the parents, were
  purebred plants
• Mendel tested sexual reproduction of the pea
  plants to see which traits would be expressed
• Mendel tested sexual reproduction of two
  different pure-bred plants that had only one
  feature (trait) that was different. (ex. Stem
  length was different between the two, but
  everything else was the exact same)

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Mendels Experiment

• The first two plants that he crossed (the
  parents) are known as the P generation
• When crossing (breeding) one pure bred tall plant
  with one pure bred dwarf plant, the resulting
  plants are called the F1 Generation and are known
  as hybrids. It turned out that in this
  particular cross, there were no dwarf plants
  produced!
• Mendel tested all varieties of plants and they
  all had the same results. The trait that was
  expressed in each case was known as the dominant
  trait. The trait that was not expressed was
  known as the recessive trait

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Mendels Experiment

• Next, Mendel crossed the F1 generations with each
  other to see if they would be all the same as the
  dominant trait parent plant. This next
  generation that resulted was known as the F2
  Generation. These plants had about 3 tall plants
  per every 1 dwarf plant (31 phenotypic ratio).
  How could you get dwarf plants from all tall
  plants?
• This means that those hybrid tall plants in the
  F1 Generation were somehow different to the P
  generation
• This pattern continued for every type of plants
  that were crossed

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Mendels Experiment

• These patterns that show, which seemed to be
  passed on to offspring are known as genes
• There can be different forms of those genes,
  which are known as alleles
• Example a gene for plant height has two
  different alleles tall and dwarf
• If a plant has 2 dominant alleles, it will be
  tall. If it has one of each, it will also be
  tall, if it has 2 recessive alleles, it will be
  dwarf
• Mendels Law of Segregation members of a pair of
  alleles for a given trait are segregated
  (separated) when gametes are formed. (meiosis)

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Mendels Experiment

• He used letters of the alphabet to represent
  genes, this genetic makeup is known as the
  genotype. He used capital letters for dominant
  and lowercase for recessive alleles. (Tall T,
  dwarf t)
• Purebred tall TT, Hybrid (phenotype is also
  tall) Tt, dwarf tt
• Genotypes with both letters the same are called
  homozygous (TT and tt)

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Mendels Experiment

• When Mendel crossed the F1 generation with each
  other, it was called a monohybrid cross.
• Each F1 plant will produce 2 different gametes T
  and t
• Those two gametes can combine with other T and t
  gametes from different cells.
• This results in 1 homozygous tall, 2
  heterozygous, and 1 homozygous dwarf plants. OR
  3 tall and 1 dwarf in a ratio 31.

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Mendels Experiment

• Once Mendel discovered that all traits worked in
  the same way, creating this 31 ratio, he moved
  on to look at 2 different traits at one time
• He chose two traits to discover and made the
  dihybrid F1 generation heterozygous again. Then
  he crossed these plants with each other. The
  cross that Mendel used for this test is called
  the dihybrid cross
• The ratio for the phenotypes of this dihybrid
  cross was 9331

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Mendels Laws

• The Law of Independent Assortment When two or
  more pairs of characteristics are considered at
  one time, each pair shows dominance and
  segregation independently of the other
• Mendels Law of Segregation members of a pair of
  alleles for a given trait are segregated
  (separated) when gametes are formed