1. Human Cerotype

3. Punnett Squares
How to predict traits in offspring

4. Important Vocabulary
1. Homozygous – when you have two of the same
genes for a particular trait
a. You are PUREBRED (2 dominant or 2 recessive)
b. TT (tall) tt (short) BB (brown eyes)
2. Heterozygous – When you have two different
genes for a particular trait
a. You are Hybrid (always 1 dominant and 1 recessive)
b. Tt (tall) Bb (brown eyes)

5. Homozygous and Heterozygous
Practice Problems
T = tall
B = brown eyes
1.
2.
3.
4.
5.
6.
t = short
b = blue eyes
Homozygous tall: _________________
Homozygous short: _______________
Heterozygous tall: ________________
Homozygous brown eyes: __________
Heterozygous brown eyes: _________
Homozygous blue eyes: ___________

6. Bikini Bottom Genetics
1. For each genotype below, indicate whether it is heterozygous
(He) or homozygous (Ho)
TT ____
Tt ____
BB ____
Bb ____
tt _____
FF ____
DD ____
dd ____
ff _____
Ff ____
Dd ____
bb _____
2. Which of the genotypes would be considered purebred?
_______________________________________________
3. Which of the genotypes would be considered hybrids?
________________________________________________

7. Punnett Squares
1. Punnett Squares – a grid showing
genetic material
-
Shows probability, not actual results
Uses percentage to predict what might
happen to the offspring
0 %, 25%, 50%, 75% or
100%

8. Punnett Square Problems
T = tall
t = short
1. A heterozygous tall man has children
with a homozygous short women.
1. Write down the genotypes of the parents
Tt
Father = _________
tt
Mother = _________

9. Step 1 – Draw a box and put a line
going down and across

10. Step 2 – Put Mother’s genes on top
of box and father’s on left hand side
t
T
t
t

11. Step 3 – bring letters down and
across

15. Completed Punnett Square
tt
t
End result:
T
Tt
t
Tt
Tt
50 % tall
_____
50 % short
_____
t
tt
tt

16. B = brown eyes
b = blue eyes
A father is homozygous for brown eyes and the
mother is homozygous for blue eyes. What is the
expected outcome?
BB
Father = ______
b
bb
Mother = ______
100 %
____
heterozygous
0
____ %
homozygous
b
B
Bb
Bb
B
Bb
Bb

17. G = Green pea
g = yellow pea
A heterozygous green pea plant is crossed with
homozygous green pea plant. What is the
expected outcome?
Gg
Plant 1 = ______
G
GG
Plant 2 = ______
50
____ %
heterozygous
50
____ %
homozygous
g
G
GG
Gg
G
GG
Gg

18. T = tall
t = short
A mother and father are both heterozygous for
being tall.
Tt
Father = ______
Tt
Mother = ______
75
____ % tall
T
t
T
TT
Tt
t
Tt
t t
25
____ % short

19. C = curly hair
c = straight hair
A dog that is purebred for straight hair is bred with
a dog that is hybrid for curly hair.
cc
Dog 1 = ______
Cc
Dog 2 = ______
50
____ %
c
C
Cc
Cc
c
cc
cc
purebred
50
____ %
hybrid
c

20. How to Make a Punnett Square.
1. Draw a square and divide it into 4
sections.
2. Write the genotypes for one parent on
the top and one down the side.
3. Fill in the sections with one allele from
top and one from the side.
4. Figure out the percentages (each box is
worth 25%)

21. Try making your own P-square!

22. Incomplete Dominance WHITE
• There’s always an
exception to the rule!
• Genes are the same
way. There are times
when a blending of
the genes occur.
• Skin color or Flower
color often does this.
RED
AND
PINK

23. Word
Incomplete
Dominance
Definition
When two traits
blend
Picture
R
E
D
A
N
D
PI
N
K