1. Punnett Squares

2. Punnett Squares
Way to show possible genotypic and phenotypic outcomes for simple genetic crosses
Shows the probability for each outcome
There are two types:
Monohybrid cross-one trait crossed
Dihybrid cross – two traits crossed

3. Section 10.1 Summary – pages 253-262
P1 generation—original parents
F1 generation—offspring of the parent plants (filial)
Ex.Your parents are P1 and you are F1
F2 generation—offspring of
the F1 generation.
Ex. Your children P1
Short pea plant
Tall pea plant
All tall pea plants F1 F2
3 tall: 1 short
Section 10.1 Summary – pages

4. Mendel’s Experiment
Mendel crossed a tall plant with a short plant and remember he got….
The offspring in the 1st generation were all tall
The offspring in the second generation, a tall and a short, were 75% tall and 25% short
Why? What happened?

5. He concluded that tall (T) must be the dominant trait and short (t) must be recessive.
Remember he crossed a tall pea plant with a short pea plant. The F1 generation were all tall.
So was the tall plant homozygous (TT) or heterozygous (Tt)? But what about the F2 Generation?!
You can do a Punnett square to figure it out!

6. Mendel’s Experiment
Crossing tall homozygous dominant pea plants with short homozygous recessive.
T = tall
t =short
TT x tt
T T t
T t
T t
Offspring
Phenotype: 4/4 or 100 % tall
Genotype: 4/4 or 100 % Tt
T t
T t

7. Mendel’s Experiment
In the next generation he got 3 tall plants and 1 short plant. Let’s see why.
T = tall
t =short
Tt x Tt
T t T t
T T
T t
Offspring
Phenotype: 75 % tall, 25 % short
Genotype: 25 % TT,
50 % Tt, 25 % tt
T t
t t

8. Mendel’s Experiment Crossing homozygous pea plants W=purple flower
w=white flower
WW x ww
Genotype: 4 Ww
Phenotype: 4 purple
0 white
W W w
W w
W w
W w
W w

9. Crossing heterozygous pea plants Ww x Ww
Genotype: 1 WW : 2Ww : 1ww
Phenotype: 3 purple
1 white