Jumpstart 11/27
Create a Venn Diagram comparing monohybrid
and dihybrid crosses.

Your venn should have at least 5 differences
and 3 similarities.
THE DIHYBRID
CROSS
Studying the inheritance of two traits
simultaneously (at the same time)
© 2007 Paul Billiet ODWS
Mendel’s peas
Character
Seed shape
Seed color
© 2007 Paul Billiet ODWS
Trait
Allele
Round
R
Wrinkled
r
Yellow
Y
Green
y
Combinations
Genotype
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy
© 2007 Paul Billiet ODWS
Phenotype
Round Yellow
Round Yellow
Round Yellow
Round Yellow
Round Green
Round Green
Wrinkled Yellow
Wrinkled Yellow
Wrinkled Green
THE LAW OF INDEPENDENT
ASSORTMENT
It appears that the inheritance of
seed shape has no influence over
the inheritance of seed color
 The two traits are inherited
INDEPENDENTLY
 The pairs of alleles that control
these two traits assort themselves
independently

© 2007 Paul Billiet ODWS
Mendel & Meiosis

The pairs of chromosomes could orientate
in different ways at Anaphase 1
© 2007 Paul Billiet ODWS
Dihybrid cross genetic diagram
P
Phenotypes Round Yellow
seed
Genotypes
Gametes
X
Wrinkled
Green seed
RRYY
rryy
meiosis
meiosis
RY
ry
fertilization
F1 Phenotypes
RrYy
Genotypes
Round Yellow
Proportions
100%
© 2007 Paul Billiet ODWS
(Pure bred)
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
Examples of FOIL- Use these
parental genotypes to find the
possible gametes:
1.
2.
3.
4.
5.
RrTt
RRTT
rrTt
RRTt
Rrtt
No need to repeat gametes if they are
the same…pay close attention!
Steps for working genetics probs
with 2 traits:
1. Assign alleles (what letters do you wanna
use?)
2. Determine genotypes of the Parents (P
generation)
3. Find gametes using FOIL method.
4. For each parent, cross off any repeats,
they are unnecessary!! (WHOO HOO….a
shortcut!)
5. Do your Punnett Square (drag n’ drop)
6. Figure it out! Analyze your Punnett
square to answer the question.
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:
Example #2
For the same pea plants:
(yellow dominant over green; and smooth dominant over wrinkled
Cross 2 pea plants that are both heterozygous
for BOTH traits.
1.
2.
3.
4.
What are the Parent genotypes?
Possible gametes?
Punnett Square?
Phenotypic ratio?
Example #1
NOW, for a shortcut!!!!
Mendel worked with peas, so let’s take an example
from him:
In pea plants, yellow color is dominant to green,
and smooth seeds are dominant to wrinkled seeds.
If a green and wrinkled plant is
crossed with a homozygous yellow
wrinkled plant, what would be the
phenotypic ratio for the offspring?