Download Punnett Squares

Warm ups:
1. Which of the following has purebred alleles?
a. Bb
b. Tt
c. Blue
d. BB
2. Which of the following would be the
phenotype for blue eyes?
a. Bb
b. blue
c. BB
d. bb
3. Which of the following would be the genotype
for a hybrid brown eyed person?
a. Brown
b. BB
c. Bb
d. bb
Important Vocabulary Review
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)
Homozygous and Heterozygous
Practice Problems
T = tall
B = brown eyes
1.
2.
3.
4.
5.
6.
t = short
b = blue eyes
TT
Homozygous tall: _________________
tt
Homozygous short: _______________
Tt
Heterozygous tall: ________________
Homozygous brown eyes: __________
BB
Heterozygous brown eyes: _________
Bb
bb
Homozygous blue eyes: ___________
Homozygous and Heterozygous
Practice Problems
7. For each genotype below, indicate whether it is heterozygous
(He) or homozygous (Ho)
Ho
TT ____
Tt ____
He
BB Ho
____
He
Bb ____
Ho
tt _____
FF ____
Ho
Ho
DD ____
dd ____
Ho
ff _____
Ho
He
Ff ____
Dd ____
He
bb _____
Ho
8. Which of the genotypes would be considered purebred?
TT, DD tt, BB, FF, dd, ff, bb
_______________________________________________
9. Which of the genotypes would be considered hybrids?
________________________________________________
Bb, Ff, Tt, Dd,
Punnett Squares
How to predict traits in offspring
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%
Punnett Square Problems
T = tall
t = short
A heterozygous tall man has children with a
homozygous short women.
Step 1: Write down the genotypes of the
parents
Father = _________
Tt
tt
Mother = _________
Step 2 – Draw a box and put a line
going down and across
Step 3 – Put a pair of genes on top of
box and a pair on the left hand side
t
T
t
t
Step 4 – bring letters down and
across
Completed Punnett Square
tt
Tt
t
t
End result:
T
Tt
Tt
50
% tall
_____
50
% short
_____
t
tt
tt
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
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
T = tall
t = short
A mother and father are both heterozygous for
being tall.
Tt
Father = ______
T
Tt
Mother = ______
75
____ % tall
t
T
TT
Tt
t
Tt
t t
25
____ % short
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 = ______
c
Cc
Dog 2 = ______
50
____ %
c
C
Cc
Cc
c
cc
cc
purebred
50
____ %
hybrid