Transcript dihybrid crosses

Dihybrid
Crosses
MONOHYBRID crosses predict
the probability of inheriting one
trait.
If the probability of inheriting
one trait can be predicted, can
the probability of inheriting two
or more traits also be
predicted?
*Dihybrid Cross*
The probability of inheriting 2 traits can
be predicted by a dihybrid cross.
Di = 2 traits
Hybrid = cross between different parents
*Dihybrid Cross*
The dihybrid cross is a 4 column x 4 row
table, representing 16 possible genetic
combinations total.
Each parent’s gametes can result in 4
possible allele combinations (hence the
4 x4 cross).
Refer to “How to Set Up a Punnett Square”
Setting up the dihybrid cross:
1. Determine the parent genotypes.
2. Determine the possible gametes that
can form when alleles segregate. Use
the FOIL method (click here next slide).
3. Place each gamete combination (2
different letters; e.g AB, aB, or ab) for
one parent over each column of the
cross
4. Do the same for the other parent to the
left of each row of the 4 x 4 cross
Follow the arrow…
*F.O.I.L method*
Sample genotype for 2 traits:
A
a
B
b
(Note: parent is heterozygous for both traits)
Possible gamete combinations:
First (AB)
Outer (Ab)
Inner (aB)
Last (ab)
Follow the arrow…
Setting up the dihybrid cross
• What are the parent genotypes?
• What possible gametes can form from the
parents genotypes when alleles segregate?
• You try!!
AaBB=
AaBb=
aaBb=
Aabb=
Parents (p1) Genotypes:
AaBb x AaBb
Offspring (F1) Genotype
Outcomes
Interpreting
the
results….
To provide the
Phenotypic
ratios you just
count the boxes
that are
displaying the
similar results.
Try this dihybrid cross…
Tall tomato plants are produced by the
action of a dominant allele T and dwarf
plants by its recessive allele t. Hairy stems
are produced by a dominant gene H and
hairless stems by its recessive allele h. A
heterozygous tall, hairy plant is crossed
with a dwarf hairless tomato plant.
Determine the phenotypic ratio for the F1
generation. Show cross and give ratio.