Intro To Genetics

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Intro To Genetics

• Probability Punnett Squares

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Gregor Mendel

• Mendel Carefully Accumulated Data And Realized
  That The
• Principles Of Probability
• Could Be Used To Explain The Results.

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Genetics Probability

• Probability
• The Likelihood That A Particular Event Will
  Occur.
• Coin Flip
• Two Possible Outcomes
• Chance of Heads Is
• 1 in 2 or 50

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Genetics Probability

• Probability of 3 Heads In A Row
• Each Toss Is An Independent Event
• Chance of 1 Head ½
• Chance of 3 Heads In Row
• ½ x ½ x ½ 1/8
• Past Outcomes Do Not Influence Future Events !

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Genetics Probability

• Key Concept
• The Principles Of Probability Can Be Used To
  Predict The Outcomes Of Genetic Crosses, Because
  Alleles Segregate As Completely Random Events.

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Genetics Probability
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Punnett Squares
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Punnett Squares

• Define The Gametes That Will Be Produced By The
  Parents.
• Place The Gametes Of One Parent Across The Top.
• Place The Gametes Of The Other Parent Down The
  Side.

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Punnett Squares

• The Gametes Represent The Alleles.
• Indicate The Genetic Makeup Of The F1 Offspring
  By Combining The Allele From Each Parent In The
  Appropriate Location In The Box

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Punnett Squares

• Capital Letters Indicate Dominant Alleles
• Lower Case Letters Indicate Recessive Alleles

T Tall t short
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Punnett Squares

• Genes Containing The Same Alleles For A Trait Are
  Said To Be
• Homozygous
• TT Homozygous Dominant
  tt Homozygous Recessive
• Genes Containing Different Alleles For A Trait
  Are Said To Be
• Heterozygous
• Tt

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Punnett Squares

• Homozygous Organisms Are Said To Be
• True Breeding
• Purebred
• Heterozygous Organisms Are Said To Be
• Hybrid

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Punnett Squares

• Phenotype
• The Physical Appearance or Characteristics Of An
  Organism.
• Genotype
• The Genetic Makeup (Alleles) Of An Organism

TT or Tt
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Punnett Squares

• Tt or TT (Tall Plants)
• One (1) Phenotype (Tall)
• Two (2) Genotypes
• True Breeding (TT)
• Hybrid (Tt)
• tt (Short Plants)
• One (1) Phenotype
• One (1) Genotype

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Probability Segregation

• Look At Fig. 11-7 (F2 Generation)
• 25 (1/4) F2 Plants Are (TT)
• 50 (1/2) F2 Plants Are (Tt)
• Therefore,
• 75 F2 Plants Are Tall
• 25 (1/4) F2 Plants Are (tt)
• Therefore,
• 25 F2 Plants Are Short

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Probability Segregation

• If Mendel Was Correct
• The Ratio Of Tall To Short Will Be 3-to-1.
• Which It Is!
• Therefore, Mendel Was Correct.
• Therefore, Segregation Is Supported By The Data.

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Probabilities Predict Averages

• Probabilities Predict The Average Outcome For A
  Large Number Of Events.
• Probability Does NOT Predict The Precise Outcome
  Of A Single Event.

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Probabilities Predict Averages

• This Is True In Genetics
• And Coin Tosses.
• The Larger The Sample Size The Closer The
  Results To Expectations.