Dihybrid Crosses (two traits)
Independent Assortment: When looking at the
inheritance of more than one trait, like ears
and fur color on a rabbit, if the traits are not
on the same chromosome, they will not always
stay together. They can sort independently of
one another. (see page 495)
When working with Dihybrid
Crosses we use the FOIL method
Example of a Dihybrid Genotype
Bb CC
First
BC
Outside
Inside
Last
BC
bC
bC
In mice, running is dominant to waltzing, and black coat color is
dominant to white. Use a punnet square to predict the results
of a cross between a heterozygous running, white mouse and a
waltzing, heterozygous black mouse.
*First we need to FOIL out the genotypes
____ ____, ____ ____ X ____ ____, ____ ____
F:
F:
O:
O:
I:
I:
L:
L:
Now we can do our Punnet Square
Genotypic Ratio:
Phenotypic Ratio:
In rabbits, black fur (B) is dominant to white fur (b) and long
hair (L) dominates short hair (l). What is the chance of
getting a black, short-haired rabbit from a cross between a
rabbit that is heterozygous for both traits and a rabbit that
is white and heterozygous for long hair?
____ ____, ____ ____ X ____ ____, ____ ____
F:
F:
O:
O:
I:
I:
L:
L:
Now do the Punnet Square
Genotypic Ratio:
Phenotypic Ratio: