KEY CONCEPT Mendel

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KEY CONCEPT Mendels research showed that traits
are inherited as discrete units.
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Mendel laid the groundwork for genetics.

• Mendel was a German friar who enjoyed gardening.
• In the mid-1800s he did many experiments crossing
  different types of pea plants
• He worked at the same time as Charles Darwin,
  read Darwins books, and believed in natural
  selection
• But nobody made the connection between Mendels
  peas and Darwins ideas until the early 1900s

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Mendel laid the groundwork for genetics.

• Traits are distinguishing characteristics that
  are inherited.
• Genetics is the study of biological inheritance
  patterns and variation.
• Gregor Mendel showed that traits are inherited as
  discrete units.
• Many in Mendels day thought traits were blended.

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Mendels data revealed patterns of inheritance.

• Mendel made three key decisions in his
  experiments.
• use of purebred plants
• controlled breeding
• observation of seveneither-or traits

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The seven traits of Mendels peas
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• Mendel used pollen to fertilize selected pea
  plants.

• Purebred plants crossed to produce F1 generation
• Prevented self-pollination by removing male
  flower parts
• Mating two organisms is called a cross.

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• Purebred organisms always produce identical
  offspring

• Mendels pea plants always made offspring with
  the same traits as parent plants.
• This means they had only one type of allele for
  each trait (homozygous).
• Heterozygous traits have two different alleles,
  but one is dominant over the other. Only dominant
  trait is expressed.

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• Mendel allowed the resulting F1 plants to
  self-pollinate.

• Among the F1 generation, all plants had purple
  flowers
• F1 plants are all heterozygous
• Among the F2 generation, some plants had purple
  flowers and some had white

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• Mendel observed patterns in the first and second
  generations of his crosses.

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• Dominant traits occur about 3 times more than
  recessive traits for all seven traits!

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• Mendel drew three important conclusions.

• Traits are inherited as discrete units.
• Organisms inherit two copies of each gene, one
  from each parent.
• The two copies segregateduring gamete formation.
• The last two conclusions arecalled the law of
  segregation.

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F1 hybrid
Mimulus lewisii
Mimulus cardinalis
Combining F1 hybrids to make F2 hybrids reveals
lots of variation because recessive alleles are
observed
Examples of F2 hybrids F1 x F1
Schemske and Bradshaw. 1999. PNAS. 9611910-11915