Mendel Carefully Accumulated Data And Realized That The Principles Of

Probability Could Be Used To Explain The

Results.

Probability=The Likelihood That A Particular Event Will Occur.

Coin FlipTwo Possible Outcomes

Chance of Heads Is1 in 2 or 50%

Probability of 3 Heads In A RowEach Toss Is An Independent Event

Chance of 1 Head = ½Chance of 3 Heads In Row =

½ x ½ x ½ = 1/8

Past Outcomes Do Not Influence Future Events !

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

1. Define The Gametes That Will Be Produced By The Parents.

2. Place The Gametes Of One Parent Across The Top.

3. Place The Gametes Of The Other Parent Down The Side.

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

Capital Letters Indicate Dominant Alleles

Lower Case Letters Indicate Recessive Alleles

T = TallT = Tall

t = shortt = short

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

Homozygous Organisms Are Said To Be:

True Breeding

Heterozygous Organisms Are Said To Be:

Hybrid

Phenotype› The Physical Appearance or

Characteristics Of An Organism.

Genotype› The Genetic Makeup

(Alleles) Of An Organism TT TT oror Tt Tt

Tt or TT (Tall Plants) One (1) Phenotype (Tall)

Two (2) Genotypes True Breeding (TT)

Hybrid (Tt)

tt (Short Plants)One (1) PhenotypeOne (1) Genotype

Look At Fig. 11-7 › 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

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.

Probabilities Predict The Average Outcome For A

Large Number Of Events.

Probability Does NOT Predict The Precise Outcome Of A

Single Event.

This Is True In Genetics And Coin Tosses.

The Larger The Sample Size – The Closer The Results

To Expectations.