Name: ________________________________________Date: ___________________ Hour: _____
Mr. Sheikh……………Pre-IB biology……………Dihybrid cross
Dihybrid Cross
In horses, black color (B) is dominant to chestnut brown (b). The trotting gait (T) is dominant
to the recessive pacing gait (t). (Gait is a slow run)
1. What are the gametes (or the sides of the punnett square) going to look like if we
mate a male Black trotter with a female Chestnut Brown pacer?
Male Gametes
Female Gametes
2. Put them in the punnett square below.
B = dominant gene
b = recessive gene
T = dominant gene
t = recessive gene
egg
sperm
3. Now, cross two horses that are heterozygous for both traits. Their genotypes would
look like this. Male BbTt x Female BbTt
Name: ________________________________________Date: ___________________ Hour: _____
Mr. Sheikh……………Pre-IB biology……………Dihybrid cross
What are the expected genotypes and phenotypes of the offspring? Use the chart
below and your punnett square.
Genotypes
BBTT __________/16
Phenotypes
Black, Trotter
____________/16
Black, Pacer
____________/16
BBTt __________/16
BBtt __________/16
BbTT __________/16
BbTt __________/16
Chestnut Brown, Trotter ___________/16
Bbtt __________/16
bbTT __________/16
bbTt __________/16
bbtt __________/16
Chestnut Brown, Pacer ____________/16