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Inheritance and Genetic Variation
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Suri Fernandes
Using a Punnett Square
Directions
1.
2.
Look at the picture.
List the things you see in the space below and
identify what each item might represent.
Fruit Fly
Letters
Capitol
Lowercase
3. What trait do you think might be represented in this picture?
Red or white eyes
4.
Calculate the probability of each trait showing up from the information in the picture and
answer the following questions:
a. How many offspring with the dominant trait might show up?
2 out of 4
b. What is the ratio of colors?
Equal
c. What percentage of offspring might have the dominant trait?
50%
d. How many offspring with the recessive trait might show up?
2 out of 4
e. What percentage of offspring might have that trait?
50%
5.
Consider the following scenario:
Tomas and Julie are about to have a child. Tomas has dark hair like his parents (DD). Julie
also has dark hair, but her mother was blonde (Dd). How can we predict what color of hair their
D
D
child might have?
D
Work with your teacher to use a Punnett square to predict the characteristics
ofDD
the child. DD
Answer the following questions.
d
Dd
a. How many DD combinations are shown?
2 out of 4
b. What color hair would these children have?
Dark Brown
c. How many Dd combinations are shown?
2 out of 4
d. What color hair would these children have?
Dark Brown
e. Is there any possible way that Tomas and Julie’s
Dd
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Inheritance and Genetic Variation
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6.
Use the abbreviation R for round peas and r for wrinkled peas in the Punnett squares for
each question. Work out the following crosses and answer the questions.
RR X rr
a. What percentage of offspring will be round?
100%
a.
0%
R
R
What percentage of offspring will be wrinkled?
r
____________________________________________________
RR X Rr
a. What percentage of offspring will be round?
100%
a.
What percentage of offspring will be wrinkled?
0%
Rr
a. What percentage of offspring will be wrinkled?
25%
R
Rr
r
R
RRr
RR
RR
___________________________________________________
Rr X Rr
a. What percentage of offspring will be round?
75%
Rr
r
Rr
Rr R
r
R
RR
___________________________________________________
Rr
rr X rr
a. What percentage of offspring will be round?
0%
a.
r
rRr
rrr
What percentage of offspring will be wrinkled?
r
100%
______________________________________________
RR X RR
a. What percentage of offspring will be round?
100%
a.
What percentage of offspring will be wrinkled?
0%
rr
rr
R
rr
r
R
rr
R
RR
RR
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Inheritance and Genetic Variation
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7.
Complete the Punnett squares from the scenarios.
Scenario 1: A man has genes of Pp. P will be dominant for
purple, and p will be recessive for white. This means his hair is
purple. A woman also has genes of Pp, and her hair is also
purple. The pair decides to have children. Determine the hair
color their children might show.
Write a ratio showing the possible colors.
3 out of 4 children will have purple hair.
What is the likelihood that a child will have white hair?
1 out of 4 children will have white hair.
_________________________________________________
Scenario 2: A man has genes of Pp, which means his hair
color is purple. A woman has genes of pp, which means her
hair color is white. They also decide to have children.
Determine the hair color their children might show.
Write a ratio showing the possible colors.
2 out of 4 children will have purple hair.
What is the likelihood that a child will have white hair?
2 out of 4 children will have white hair.
_______________________________________________
Scenario 3: A man has genes of BB, which means his eye
color is brown. A woman has genes of bb, which means her
eye color is blue. They decide to have children. Determine the
eye color their children might show.
Write a ratio showing the possible colors.
4 out of 4 children will brown eyes.
What is the likelihood that a child will have blue eyes?
0 out of 4 children will have blue eyes.
_________________________________________________
Scenario 4: A man has genes of bb, which means his eye
color is blue. A woman has genes of Bb, which means her eye
color is brown. They decide to have children. Determine the
eye color their children might show.
Write a ratio showing the possible colors.
2 out of 4 children will have blue eyes.
What is the likelihood that a child will have blue eyes?
2 out of 4 will have brown eyes.
P
P
p
p
p
b
b
B
b
PP
p
Pp
Pp
pp
P
p
Pp
pp
Pp
pp
B
B
Bb
Bb
Bb
Bb
b
b
Bb
bb
Bb
bb
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Inheritance and Genetic Variation
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Questions
1. How are genes represented in a Punnett square?
Punnett Square makes use of a grid and letters. In particular, capital letters represent dominant
alleles and lower case letters to recessive alleles.
2. Does every gene combination show up in the offspring?
No, not every gene combination shows up in the punnett square.
3. How many possible offspring are predicted in each Punnett square?
There are only 4 predictions in the Punnett square, but they’re not 100% true.
4. When thinking about genotypes and phenotypes, which is the cause and which is the
effect?
Genotypes is the cause and the phenotype is the effect.
5. When observing an organism’s phenotype, how can we predict the genotype?
We can predict the genotype by using the Punnett square and crossing them together.
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