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% 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)

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

Cross between hybrid tall pea plants Mom Tt Dad Tt

Cross between hybrid tall pea plants Mom Tt Dad Tt

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

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

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

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

Frayer Model

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