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Mendelian

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					     Genetics
A study of inheritance


 Thanks to Mr. Byman, MMHS Biology 12/05/05
Gregor Mendel
       • Father of modern
         genetics
Gregor Mendel
       • Father of modern
         genetics
       • Researched with
         pea plants
Gregor Mendel
       • Father of modern
         genetics
       • Researched with
         pea plants
       • Developed ideas of
         dominance and
         trait segregation
Phenotype
     • Phenotype
       – Physical
         characteristics
Genotype
    • Phenotype
      – Physical
        characteristics


    • Genotype
      – Genes we inherit from
        our parents
Phenotype

     Notice the similarities:
       – Facial structure
Phenotype

     Notice the similarities:
       – Facial structure
       – Eyes
Phenotype

     Notice the similarities:
       – Facial structure
       – Eyes
       – Smile
Phenotype

     Notice the similarities:
       –   Facial structure
       –   Eyes
       –   Smile
       –   Ears
Phenotype

     Notice the similarities:
       –   Facial structure
       –   Eyes
       –   Smile
       –   Ears
       –   Nose
Phenotype

     Notice the similarities:
       –   Facial structure
       –   Eyes
       –   Smile
       –   Ears
       –   Nose
       –   Neck
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
   •Seed coat color - white or GRAY
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
   •Seed coat color - white or GRAY
   •Pod shape - constricted or SMOOTH
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
   •Seed coat color - white or GRAY
   •Pod shape - constricted or SMOOTH
   •Pod color - yellow or GREEN
          Mendelian Genetics
Mendel studied a number of characteristics in pea plants
including:

   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
   •Seed coat color - white or GRAY
   •Pod shape - constricted or SMOOTH
   •Pod color - yellow or GREEN
   •Flower position - terminal or AXIAL
          Mendelian Genetics
We will work the following three:


   •Height - short or TALL
   •Seed color - green or YELLOW
   •Seed shape - wrinkled or ROUND
   •Seed coat color - white or GRAY
   •Pod shape - constricted or SMOOTH
   •Pod color - yellow or GREEN
   •Flower position - terminal or AXIAL
       Predicting Inheritance
To determine the chances of inheriting a given
trait, scientists use Punnett squares and symbols
to represent the genes.

UPPERCASE letters      are   used   to   represent
dominant genes.

lowercase letters are used to represent recessive
genes.
         Predicting Inheritance
For example:
T = represents the gene for TALL in pea plants
t = represents the gene for short in pea plants

So:
TT & Tt both result in a TALL plant, because T is
dominant over t. t is recessive.
tt will result in a short plant.

Remember there are two genes for every trait!
         Predicting Inheritance
For example:
       Mendels’ Principle of Dominance
T = represents the gene for TALL in pea plants
Some genes (alleles) are dominant pea plants
t = represents the gene for short inand others are
recessive. The phenotype (trait) of a dominant gene
will
So: be seen when it is paired with a recessive gene.
TT & Tt both result in a TALL plant, because T is
dominant over t. t is recessive.
tt will result in a short plant.

Remember there are two genes for every trait!
        Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a
short plant (tt).
Each plant will give only one of its’ two genes to
the offspring or F1 generation.

                      TT x tt


              T      T          t    t
        Predicting Inheritance
Let’s cross a totally dominant tall plant (TT) with a
        Mendels’
short plant (tt). “Law” of Segregation
Each plant will give only one of its’ two genes to
Each gene (allele) separates from
the offspring or F1 generation. the other so that
the offspring get only one gene from each parent for a
given trait.
                      TT x tt


              T       T         t    t
Punnett Squares



      Tt              Tt
    The genes from one parent go here.

    The genes from the other parent go
    here.
      Tt              Tt
     Punnett Squares

           T    P1   T

 t         Tt        Tt
P2
 t         Tt        Tt
    Punnett Squares

          T       T

t         Tt      Tt

t         Tt      Tt
    Punnett Squares

          T       T

t         Tt      Tt

t         Tt      Tt
    Punnett Squares

          T       T

t         Tt      Tt

t         Tt      Tt
    Punnett Squares

          T       T

t         Tt      Tt

t         Tt      Tt
    Punnett Squares

          T        T

t         Tt      Tt
         F1 generation
t         Tt      Tt
   Interpreting the Results
The genotype for all the offspring is Tt.
The genotype ratio is:
                Tt - 4/4

The phenotype for all the offspring is tall.
The phenotype ratio is:
                tall - 4/4
     Punnett Squares

           T       t

      Turn!!
Your ?? ??
 T

 t         ??      ??
    Punnett Squares

          T        t

T        TT       Tt
         F2 generation
t         Tt      tt
            Punnett Squares
Next, give the genotype and phenotype
                   T          t
ratios of the offspring (F2 generation).

        T         TT         Tt

        t         Tt         tt
           Punnett Squares
Genotype ratio: TT - 1
                         T   t

      T              TT      Tt

       t             Tt      tt
           Punnett Squares
Genotype ratio: TT - 1, Tt - 2
                       T         t

       T              TT         Tt

       t              Tt         tt
            Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
                        T                t

       T               TT                Tt

        t              Tt                tt
            Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
                        T                t
Phenotype ratio: Tall - 3


       T               TT                Tt

        t              Tt                tt
            Punnett Squares
Genotype ratio: TT - 1, Tt - 2, tt - 1
                        T                t
Phenotype ratio: Tall - 3, short - 1


       T               TT                Tt

        t              Tt                tt
           Punnett Squares

This is a monohybrid T            t
                     cross. We worked with
only one trait. The height of the plant.

       T          TT          Tt

       t          Tt          tt
            Punnett Squares

This is a monohybrid T            t
                     cross. We worked with
only one trait. The height of the plant.

                                    two
       Twe
Tomorrow      will
                    TT
                  work with  a
                                  Tt
                               dihybrid cross,
using the height of the plant and either seed
color or seed shape.
        t           Tt           tt
 Homework - Punnett Squares

               T         t
Questions 1 & 2 on Rats Practice
Problems and question 1 on Foxes
      T       TT         Tt
and Watermelons Practice Problems.

      t        Tt       tt

				
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