Mendelian Genetics

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Mendelian Genetics
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Father of Modern Genetics

• Austrian monk, high school teacher, and part-time
  garden keeper
• First to propose biological inheritance of traits
• Work not recognized until after his death

Gregor Mendel
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Why pea plants?

• Its what he had
• They grow fast
• Pea plants are true breeding
• Gregor noticed that one stock of seed would
  produce only tall plants and another only short
  plants

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Traits

• Specific characteristics that vary from one
  individual to the next
• Hair color
• Eye color
• Seed color
• Flower color

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Mendels Experiment
Cross-pollination
P generation
Next, Mendel wanted to find out if the white
alleles had disappeared, or were they still
present in the F1 generation.
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Vocabulary

• P generation parental
• F1 first son the offspring of the P
  generation
• F2 second son the offspring of the F1 cross
• Phenotype the physical characteristics, what the
  trait looks like
• Hybrid cross between parents with different
  versions of the trait.

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• Mendel crossed the F1 generation with itself
• He found that the white flower trait reappeared
  in some of the F2 generation

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Perplexed?

• Conclusion One inheritance is due to factors
  that are passed from one generation to the next
• Today, we call those factors GENES
• Allele different forms of a gene (like pink vs
  white for flower color)
• Conclusion Two some alleles are dominant and
  others are recessive

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How did the white trait reappear?

• He proposed this was due to segregation of
  alleles during formation of gametes.

What are these called? What process made them?
What are these called?!
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• Homozygous two copies of the same allele
• Dominant AA
• Recessive aa
• TRUEBREEDING
• Heterozygous different alleles (Aa)

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Practice Cats

• What trait is represented by T and t?
• NN phenotype or genotype?
• Long hair phenotype or genotype?
• A homozygous tabby cat would have what genotype?
• A cat that is nn would have what phenotype?

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Applying and practicing your vocab

• Crazy Traits
• Exit Slip
• Vocab quiz on Wednesday

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Probability

• Mendel categorized and counted the many offspring
  of each of his experiments.
• He noticed that each time he repeated a
  particular cross he obtained similar results.

• For example
• Every time he crossed two plants that were
  heterozygous for stem height (Tt), about ¾ of the
  offspring were tall and ¼ were short.

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Probability and Punnett Squares

• Punnett squares are used as a tool to predict
  this probability
• Monohybrid crosses can be performed to determine
  probability of phenotype for one particular trait

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Genotypes
AA
Homozygous Dominant
Aa
Heterozygous
aa
Homozygous Recessive