Mendelian Genetics
All Materials Cmassengale 

Mendel 1862

Mendel 1868 Mendel 1880
1862 1868 1880

Genetic Terminology:

Blending Concept of Inheritance:

Gregor Mendel:

drawing of a flower cross-section showing both male and female sexual structures

Why peas, Pisum sativum?

Picture of Pisum sativum
GARDEN PEA

Mendel's Experiments:

            a. Seed shape ---  Round (R) or Wrinkled (r)
            b. Seed Color ---- Yellow (Y) or  Green (y)
            c. Pod Shape --- Smooth (S) or wrinkled (s)
            d. Pod Color ---  Green (G) or Yellow (g)
            e. Seed Coat Color ---  Gray (G) or White (g)
            f. Flower position --- Axial (A) or Terminal (a)
            g. Plant Height --- Tall (T) or Short (t)
            h. Flower color --- Purple (P) or white (p)


 

              Trait - plant height

              Alleles - T tall, t short

F1 cross    Tt  x  Tt

genotype      --    TT, Tt, tt
  T t   phenotype    --    Tall & short
T TT Tt   genotypic ratio --1:2:1
t Tt tt   phenotypic ratio- 3:1

 

Trait   -  Plant Height

Alleles - T  tall, t  short

F2 cross       TT  x Tt

F2 cross       tt  x Tt

  T t     T t  
T TT Tt   t Tt tt  
T TT Tt   t Tt tt  
               

          genotype - TT, Tt

            genotype - tt, Tt  

          phenotype  -  Tall

            phenotype  -  Tall & short  

          genotypic ratio  - 1:1

            genotypic ratio  - 1:1  

          phenotypic ratio - all alike

            phenotypic ratio - 1:1  

Problems: Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be sure to include genotypes, phenotypes, genotypic & phenotypic ratios.

Traits:      Seed Shape & Seed Color

Alleles:     R round                Y yellow
                 r wrinkled             y green

 P1 Cross:     RRYY          x     r r yy  

      

  ry  

Genotype:

     RrYy

RY

RrYy

 

Phenotype:

     Round yellow seed

Genotypic ratio:

     All alike
     

Phenotypic ratio:

     All Alike

 

Traits:       Seed Shape & Seed Color

Alleles:     R round                Y yellow
                 r wrinkled             y green

     F1 Cross:     RrYy           x     RrYy                            

  RY Ry rY ry
RY
RRYY

RRYy

RrYY

RrYy
Ry
RRYy

RRyy

RrYy

Rryy
rY
RrYY

RrYy

r rYY

r rYy
ry
RrYy

Rryy

r rYy

r ryy

 

Genotypes Genotypic Ratios

Phenotypes

Phenotypic Ratios

RRYY 1

Round yellow seed

9

RRYy 2
RrYY 2
RrYy 4
RRyy 1

Round green seed

3
Rryy 2
r rYY 1

Wrinkled yellow seed

3
r rYy 2
r ryy 1

Wrinkled green seed

1

Problems: Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios. 

Results of Mendel's Experiments:

Trait: Pod Color
Genotypes: Phenotype:
GG Green Pod
Gg Green Pod
gg Yellow Pod

Rr

R r

RrYy

RY Ry rY ry

 

Other Patterns of Inheritance:

Genotype Phenotype
IOIO Type O
IAIO Type A
IAIA Type A
IBIO Type B
IBIB Type B
IAIB Type AB