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Probability and Punnett Squares

Probability and Punnett Squares. Introduction to Genetics Honors Biology Chapter 11 Section 2. Genetics and Probability. The likelihood that a particular event will occur is called probability Ex: Flip a coin, the probability it will land on heads is 1 in 2. This is ½ or 50%

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Probability and Punnett Squares

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  1. Probability and Punnett Squares Introduction to Genetics Honors Biology Chapter 11 Section 2

  2. Genetics and Probability • The likelihood that a particular event will occur is called probability Ex: Flip a coin, the probability it will land on heads is 1 in 2. This is ½ or 50% Flip the coin 3 times in a row and the probability of flipping 3 heads in a row is 1/8 ½ x ½ x ½ = 1/8 You have 1 chance in 8 of flipping heads 3 times in a row • A coin is similar to genetics because alleles separate randomly, just like flipping a coin. We can predict the outcomes of genetic crosses (Punnett Squares)

  3. Punnett Squares • The types of gametes that can be produced from one parent are on one side and the gametes from the other parent are lined up along the other side • The possible combinations of the F2 generation are found inside the squares • The letters represent alleles. Capitol letters are dominant and little letters are recessive EX: plant height tall = TT or Tt Short = tt

  4. Cross between hybrid tall pea plants Mom Tt Dad Tt

  5. Cross between hybrid tall pea plants Mom Tt Dad Tt

  6. Punnett Squares • The square can be used to predict and compare genetic variations that result from a cross • Organisms with 2 identical alleles for a trait (TT or tt) are called homozygous • Organisms with 2 different alleles for a trait (Tt) are called heterozygous

  7. Punnett Squares • All tall plants have the same phenotype, or physical characteristics • They do not contain the same genotype, or genetic makeup EX: a tall plant phenotype is tall genotype is TT or Tt

  8. Probability and Segregation • In the F1 heterozygous hybrid cross, ¾ of the plants should be tall ¼ TT ½ (¼ + ¼) Tt • ¼ of the plants should be short ¼ tt • The 3:1 ratio of dominant to recessive • Segregation occurred according to Mendel’s model

  9. Probabilities Predict Averages • The more offspring, the closer you will come to reaching your predicted outcomes. Hundreds and Thousands of individuals • The same can be applied to coin flipping • This is because probabilities predict the outcome of a LARGE number of events

  10. Frayer Model

  11. Frayer Model Assignment Create a Frayer Model for each of the following words • Trait • Phenotype • Genotype

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