1. Dihybrid Crosses

2. What is a Dihybrid Cross?
Is a cross that involves two different traits.
T t P p X T t P p
What do these symbols mean?
T = tall
t = short
P = purple flower
p = white flower

3. When working with Dihybrid Crosses we use the FOIL method
Example of a Dihybrid Genotype
Bb CC
First Outside Inside Last
BC BC bC bC

4. Punnett Square Heterozygous dihybrid cross T t P p X T t P p T p T P

5. T p Dominant traits – T – tall P – purple flowers T P T p
T T P P
T P
T T P p
T t P P
T t P p
T p
T T P p
T T p p
T t P p
T t p p
Recessive traits –
t – short
p - white
t P
T t P p
T t P P
t t P P
t t P p
t p
T t p p
T t P p
t t P p
t t p p
Phenotypic results
Short & white
Tall &Purple
Short & Purple
Tall & White 9 3 3 1
Phenotypic ratio is 9 tall & purple: 3 short & purple: 3 tall & white: 1 short & white

6. The Law of Independent Assortment
The genes for traits such as flower color and height sort independently.
Which means that the gene for flower color is not linked with the gene for height, just because a flower is tall, doesn’t mean it will also be purple.