NAME___________________________
DATE___________________
HOUR___________________
BIOLOGY I - DIHYBRID CROSSES
HEREDITY - 5
INTRODUCTION – Crosses involving two traits can be followed with a Punnett square just like a Monohybrid. It just
requires a larger square. These types of crosses are called Dihybrids. The major difference is that when following one trait, the
parent can produce a maximum of two gametes. With two triats, a dihybrid, the parent could produce as many as four gametes.
For example, look at a plant that is heterozygous for tallness and heterozygous for pod color. Its genotype would be TtGg. It
can produce four different gametes. Any one of these gametes could be passed on: TG, Tg, tG, and tg. Here is an example of a
Dihybrid cross:
TtGg X TtGg
TG
Tg
tG
tg
TG
TTGG
TTGg
TtGG
TtGg
THE RESULTS:
Tg
TTGg
TTgg
TtGg
Ttgg
tG
TtGG
TtGg
ttGG
ttGg
tg
TtGg
Ttgg
ttGg
ttgg
9 TALL GREEN PLANTS
3 TALL YELLOW PLANTS
3 SHORT GREEN PLANTS
1 SHORT YELLOW PLANT
PROBLEMS – Use the table below to solve the following problems. Determine the gametes that will be produced.
Then using a Punnet square, predict the offspring of the cross.
1. Cross a tall brown plant with a short white plant: TTBB X ttbb
What gametes can the first plant produce? _________ What gametes can the second plant produce? _________
How many of these plants are Tall and Brown?______
How many of these plants are Tall and White?________
How many of these plants are Short and Brown?______
How many of these plants are Short and White?________
2. Cross two Tall and Brown plants TtBb x TtBb.
What gametes can the first plant produce? _________ _________ _________ _________
What gametes can the second plant produce? _________ _________ _________ _________
How many of these plants are Tall and Brown?______
How many of these plants are Tall and White?________
How many of these plants are Short and Brown?______
How many of these plants are Short and White?________
3. Cross a Green and Tall plant with a Yellow and Short plant. GGTT x ggtt
What gametes can the first plant produce? _________ What gametes can the second plant produce? _________
What is the phenotypic ratio??_________________________
4. Cross two Green and Tall plants GgTt x GgTt.
What gametes can the first plant produce? _________ _________ _________ _________
What gametes can the second plant produce? _________ _________ _________ _________
What is the phenotypic ratio??_________________________
5. Cross two Green and Round plants GgRr x GgRr
(ggrr would be a Yellow and Wrinkled plant)
What gametes can the first plant produce? _________ _________ _________ _________
What gametes can the second plant produce? _________ _________ _________ _________
What is the phenotypic ratio??_________________________
6. Cross two Round and Tall plants RrTt x rrtt
(rrtt would be a Wrinkled and Short plant)
What gametes can the first plant produce? _________ _________ _________ _________
What gametes can the second plant produce? _________ _________ _________ _________
How many of these plants are Round and Tall?______
How many of these plants are Round and Short?________
How many of these plants are Wrinkled and Tall?______
How many of these plants are Wrinkled and Short?________