Introduction to Genetics The Work of Gregor Mendel

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Introduction to GeneticsThe Work of Gregor
Mendel
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• Genetics the scientific study of heredity
• Father of Genetics - Gregor Mendel
• Worked with garden peas and studied 7 different
  traits.
• He asked Why do pea plants have different
  traits?

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• Trait a characteristic that varies among
  individuals (Example seed color, plant height,
  eye color, type of earlobes)
• Mendel used true breeding plants - produced
  offspring identical to themselves
• He then Cross Pollinated plants - joined cells
  from two different plants
• Offspring had the characteristics of only ONE of
  the parents

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Mendels Seven F1 Crosses on Pea Plants
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• Mendel Concluded
• 1. Biological inheritance is determined by genes
• Alleles - different forms of a gene
• Examples Gene Height Alleles Tall or Short
• Gene Ear lobe type Alleles Attached
  or Unattached
• 2. The Principle of Dominance - some alleles are
  dominant and others are recessive

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• Dominant allele - will always appear
• Capital letter (T)
• Recessive allele - ONLY appears when TWO are
  present
• Lowercase letter (t)
• Examples
• TT and Tt tall
• tt short

SPECIAL NOTE use the SAME letter for the same
gene capital for the dominant trait and
lowercase for the recessive trait ?
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• Mendel then wondered if the recessive alleles
  disappeared in the plants he crossed first or
  were they still present?
• He crossed these plants and discovered.

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P Generation
F1 Generation
F2 Generation
Tall
Short
Tall
Tall
Tall
Tall
Tall
Short
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• That the recessive traits had reappeared!
  (instead of all plants being tall there were now
  some short ones!)
• Why?
• The recessive allele had been separated from the
  dominant allele
• Segregation the separation of alleles during
  gamete formation (Meiosis!)