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Warm Up

  • What is probability? How does it relate to genetics?

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  • Get ready to take quiz (half sheet of paper)

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Lesson Goal: To learn about probability & punnett squares.

Agenda:

  • Warm Up
  • Quiz
  • Lecture
  • CW/HW

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�Probability and Punnett Squares�

Section 11–2

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Probability

The likelihood that a particular event will occur is called_______.

  • Probability

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Which letter represents the probability that a single coin flip will come up heads.

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  • a. 100 percent
  • b. 75 percent
  • c. 50 percent
  • d. 25 percent

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  • Is the following sentence true or false?
  • The past outcomes of coin flips greatly affect the outcomes of future coin flips.
  • False

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  • Why can the principles of probability be used to predict the outcomes of genetic crosses?
  • The way in which the alleles segregate is completely random, like a coin flip.�

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How do geneticists use Punnett squares?

  • Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

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Video: Punnett Squares

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Complete the Punnett square to show the possible offspring.

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Tt X Tt

T = tall

t= short

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Allele Types

  • Homo - Same
  • Hetero –Other/Opposite
  • Pheno – Physical
  • Geno - Genetic

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Definitions

  • Organisms that have two identical alleles
    • particular trait (TT or tt) Homozygous
  • Organisms that have two different alleles

-same trait (Tt) Heterozygous

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  • Physical characteristic of an organism Phenotype
  • Genetic makeup of an organism (Tt) Genotype

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Gene Expression�

Are the following sentences true or false?

- Homozygous organisms are true breeding for a particular trait.

  • True

- Plants with the same phenotype always have the same genotype.

  • False

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Practice Problem

  • Dad is heterozygous brown eyes mom is homozygous recessive, blue eyes.
  • Brown is dominant

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Problem #2

  • Cross between a homozygous recessive black chicken and a heterozygous blue chicken.

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HW

  • Complete worksheet
  • Vocabulary 11-2
  • Worksheets 11-2

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Segregation and ratios

  • The F2 ratio of tall plants to short plants produced in a cross between two hybrid tall pea plants (Tt) is 3 tall plants for every 1 short plant.
  • Mendel observed that about 3⁄4 of the F2 offspring showed the dominant trait.
  • Segregation occurs according to Mendel’s model.

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  • In Mendel’s model of segregation, what was the ratio of tall plants to short plants in the F2 generation?

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  • The ratio was 3 : 1.

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  • Is the following sentence true or false?

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  • Probabilities predict the precise outcome of an individual event.

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  • False

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  • How can you be sure of getting the expected 50 : 50 ratio from flipping a coin?�
  • You must flip the coin many times.�

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The larger number of offspring from a genetic cross, the closer the resulting numbers will get to expected values.

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Probability

Is the following sentence true or false?

  • The ratios of an F1 generation are more likely to match Mendelian predicted ratios if the F1 generation contains hundreds or thousands of individuals.

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  • True

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