NAME ___ANSWER KEY________________
PUNNETT SQUARE PRACTICE #1
Use a Punnett Square to show the possible offspring from the crosses given and answer the questions:
IN PEAS:
R = round
r = wrinkled
t = short
T = tall
Y = yellow peas
P = purple flowers
y = green peas
p = white flowers
MAKING MONOHYBRID CROSSES:
Use colors to circle the offspring with the same phenotype.
Y
Y
Yy
Yy
What is the genotype of a HOMOZYGOUS YELLOW SEED plant? = __YY_____
What is the genotype of A HOMOZYGOUS GREEN SEED plant? = ___yy_____
y
What is the genotype of a HETEROZYGOUS YELLOW plant? = ___Yy_____
y
Yy
Yy
Make a cross between a PURE YELLOW SEED parent and a PURE GREEN SEED parent.
POSSIBLE OFFSPRING
GENOTYPE
PHENOTYPE
__Yy_______
__Yellow seeds_______________
What is the probability an offspring will show the DOMINANT TRAIT (YELLOW SEEDS)? __100% or 4/4_______
What is the probability an offspring will show the RECESSIVE TRAIT (GREEN SEEDS)? _0% or 0/4_______
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MAKING MONOHYBRID CROSSES:
Use colors to circle the offspring with the same phenotype.
P
P
What is the genotype of a PURE PURPLE FLOWERED plant ? = _PP_______
What is the genotype of a PURE WHITE FLOWERED plant? = __pp_______
p
Pp
Pp
p
Pp
Pp
What is the genotype of a HYBRID PURPLE FLOWERED plant? = _Pp_______
Make a cross between a HOMOZYGOUS PURPLE FLOWERED plant and a HOMOZYGOUS WHITE
FLOWERED plant.
POSSIBLE OFFSPRING
GENOTYPE
PHENOTYPE
__Pp______
__purple flowers_______________
What is the probability an offspring will show the DOMINANT TRAIT (PURPLE FLOWERS)? _100% or 4/4__________
What is the probability an offspring will show the RECESSIVE TRAIT (WHITE FLOWERS)? _0% or 0/4____________
SEE A PATTERN FOR HOMOZYGOUS MONOHYBRID CROSSES:
If you cross plants that are PURE DOMINANT for a trait with plants that are PURE RECESSIVE for that trait, _100___ % of the offspring will
show the DOMINANT trait and the _recessive________ trait will not show at all.
USE THE PATTERN ABOVE TO MAKE PREDICTION ABOUT A CROSS
If you cross a HOMOZYGOUS ROUND SEED plant with a PURE WRINKLED SEED plant
100% will look __Round________________
0% will look ___Wrinkled_________________
The offspring will have a 100% probability of having the _Rr_____ genotype.
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3. MAKE SOME HETEROZYGOUS MONOHYBRID CROSSES
B
A black coat (B) is DOMINANT in guinea pigs. A brown coat (b) is RECESSIVE.
b
What is the genotype of a HOMOZYGOUS BLACK guinea pig? = __BB_____
B
BB
Bb
What is the GENOTYPE of a HETEROZYGOUS BLACK guinea pig? =__Bb_______
What is the GENOTYPE of a brown guinea pig? =__bb________
b
Bb
bb
Make a cross between TWO HETEROZYGOUS BLACK guinea pigs.
POSSIBLE OFFSPRING
GENOTYPE
PHENOTYPE
___BB________
__black_______________
___Bb________
__black________________
__bb_________
___brown______________
What is the probability that a baby will be black? __3/4_______
What is the probability that a baby will be brown? __1/4_______
What is the probability the baby will be a HYBRID? __1/2______
What is the probability the baby will be HOMOZYGOUS DOMINANT ? _1/4________
What is the probability the baby will be HOMOZYGOUS RECESSIVE? ___1/4________
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4. Purple fur (P) is DOMINANT in monsters. Yellow fur (p) is RECESSIVE.
P
p
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*
What is the genotype of a PURE PURPLE monster? = _PP_______
What is the GENOTYPE of a HETEROZYGOUS purple monster? __Pp_______
P
PP
Pp
What is the GENOTYPE of a YELLOW monster? = ___pp_____
Make a cross between TWO HETEROZYGOUS PURPLE MONSTERS.
p
Pp
pp
GENOTYPES
POSSIBLE OFFSPRING
PHENOTYPES
_PP__________
___purple______________
_Pp__________
___purple______________
__pp_________
___yellow______________
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What is the probability that a baby will be purple ? _3/4_________
What is the probability that a baby will be yellow? _1/4_________
What is the probability the baby will be a heterozygous? _1/2________
What is the probability the baby will be HOMOZYGOUS DOMINANT ? __1/4_______
What is the probability the baby will be HOMOZYGOUS RECESSIVE? ____1/4_______
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SEE A PATTERN FOR HETEROZYGOUS MONOHYBRID CROSSES:
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If you cross 2 parent plants that are BOTH HETEROZYGOUS for a trait the offspring will show a _3 : 1____ phenotypic ratio.
__75___ % of the offspring will show the DOMINANT trait and
__25___ % of the offspring will show the RECESSIVE trait.
USE DOMINANT OR RECESSIVE TO FILL IN THE BLANKS BELOW:
¼ of the offspring will have two __dominant_________ alleles,
½ will be hybrids with one __dominant_____ and one ___recessive__ allele, and
¼ will have two ___recessive______ alleles.
USE THE PATTERN ABOVE TO MAKE PREDICTION ABOUT A CROSS
If you cross two HETEROZYGOUS ROUND SEED plants
75% will look _____Round_____________
25% will look ______Wrinkled____________
The probability is:
¼ will have the genotype _RR__
½ will have the genotype _Rr__ ¼ will have the genotype _rr__
Scientists have been investigating the genetic make up of the residents in Bikini Bottom.
Complete the following questions about these inhabitants.
For each genotype below, indicate whether it is HETEROZYGOUS (HE) or HOMOZYGOUS (HO).
TT __HO_____
Bb ___HE__
DD ___HO__
tt ___HO___
Ff ___HE__
Dd __HE_____
ff ___HO___
bb ___HO__
BB __HO___
FF __HO__
Determine the PHENOTYPE for each genotype given. IN SPONGE PEOPLE the allele for YELLOW BODY COLOR (Y) is DOMINANT to BLUE
(y).
YY = ___yellow________ Yy = __yellow__________
yy = __blue____________
IN SPONGEPEOPLE the allele for SQUARE SHAPE (S) is dominant to ROUND (s).
SS = __square_________
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Ss = __square___________
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ss = ____round___________
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5. SpongeBob Squarepants recently met SpongeSuzie Roundpants at a dance.
SpongeBob is HETEROZYGOUS for his square pants, but Suzie is ROUND.
Use the gene code above to create a Punnett square to show the possibilities that could result if SpongeBob and SpongeSuzie had children.
S
What is Spongebob’s genotype? ____Ss_________
s
What is Spongesuzie’s genotype? ____ss_______
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s
Ss
ss
What are the chances a child will have a square shape?
__2______ out of 4 OR _50______%
s
Ss
ss
What are the chances a child will have a round shape?
__2______ out of 4
OR __50_____%
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In SQUID PEOPLE the allele for LIGHT BLUE SKIN (B) is DOMINANT over the GREEN (b) allele. Everyone in Squidward’s family
has light blue skin. His family brags that they are a “purebred” line. He recently married a nice girl with light green skin, which is
recessive. Create a Punnett square to show the
possible offspring from this match.
B
List the possible genotypes and phenotypes for the kids
B
_Bb________
b
Bb
b
What are the chances of a child with green skin? __0____%
Bb
Bb
Bb
__Light blue skin____________
Would Squidward’s children still be considered “purebreds”?
EXPLAIN WHY or WHY NOT.
YES
NO
All of Squidward’s children are hybrids and could potentially pass green skin on to their own children.
H
H
d
Hd
Hd
d
Hd
Hd
H
d
d
Hd
dd
d
Hd
dd
T
T
t
Tt
Tt
t
Tt
Tt
T
t
t
Tt
tt
t
Tt
tt
PUNNETT SQUARES #3
IN PEAS:
R = round
r = wrinkled
T = tall
t = short
Y = yellow peas
P = purple flowers
y = green peas
p = white flowers
8. MAKING HOMOZYGOUS TWO GENE CROSSES: (X = crossed with)
Use colors to circle the offspring with the same phenotype.
HOMOZYGOUS
TALL & ROUND
Parent genotype
__TTRR____________
Possible gametes
_TR___
X
PURE
SHORT & WRINKLED
____ttrr_______________
_tr___
tr
What percent will be?
TR
__100% TALL & ROUND
__0___ SHORT & ROUND
TtRr
__0___ TALL & WRINKLED
__0___ SHORT & WRINKLED
SEE A PATTERN FOR HOMOZYGOUS TWO GENE CROSSES:
If you cross plants that are PURE DOMINANT for TWO TRAITS with plants that are PURE RECESSIVE for
TWO TRAITS, __100___ % of the offspring will look DOMINANT for BOTH traits and the
__recessive_________ traits will not show at all.
9. MAKING HETEROZYGOUS DIHYBRID CROSSES:
Use different colors to circle the offspring with the same PHENOTYPE
HETEROZYGOUS
TALL & ROUND
Parent genotype
__TtRr____________
Possible gametes
_TR_ _Tr_ _tR_ _tr_
X
HYBRID
TALL & ROUND
___TtRr_______________
_TR___ _Tr___ _tR___ _tr___
TR
Tr
tR
tr
TR
TTRR
TTRr
TtRR
TtRr
__3/16__ TALL WRINKLED
Tr
TTRr
TTrr
TtRr
Ttrr
__9/16_____ TALL ROUND
tR
TtRR
TtRr
ttRR
ttRr
__1/16_____ SHORT WRINKLED
tr
TtRr
Ttrr
ttRr
ttrr
__3/16_____ SHORT ROUND
What is the probability the offspring will be
10. MAKING HETEROZYGOUS DIHYBRID CROSSES:
Use different colors to circle the offspring with the same PHENOTYPE.
HYBRID TALL
with YELLOW PEAS
X
HETEROZYGOUS TALL
with YELLOW PEAS
Parent genotype
__TtYy_____________
___TtYy___________________
Possible gametes
TY_ _Ty_ _tY_ _ty_
_TY_ _Ty__ tY_ ty_
TY
Ty
tY
ty
What is the probability the offspring will be
TY
TTYY
TTYy
TtYY
TtYy
__3/16_ SHORT w/ YELLOW PEAS
Ty
TTYy
TTyy
TtYy
Ttyy
tY
TtYY
TtYy
ttYY
ttYy
ty
TtYy
Ttyy
ttYy
ttyy
__3/16_ TALL w/ GREEN PEAS
_1/16__ SHORT w/ GREEN PEAS
_9/16__ TALL w/ YELLOW PEAS
FIND THE PATTERN FOR HETEROZYGOUS DIHYBRID CROSSES :
If you cross 2 parent plants that are BOTH HETEROZYGOUS for TWO TRAITS, the offspring will show a
__9_ : _3_ : _3_ : _1_ phenotypic pattern.
Fill in the blanks below with: DOMINANT or RECESSIVE
9/16 of the offspring will show both __dominant__________ traits.
3/16 will look _dominant________ for trait 1 and __recessive______ for trait 2.
3/16 will look __recessive________ for trait 1 and __dominant______ for trait 2.
1/16 will look __recessive_________ for both traits.
USE THIS PATTERN TO TELL THE POSSIBLE OFFSPRING OF A HETEROZYGOUS DIHYBRID
CROSS WITHOUT USING A PUNNETT SQUARE:
R = round
r = wrinkled
T = tall
t = short
RrTt
X
RrTt
9/16 will look Round and Tall
3/16 will look Round and Short
3/16 will look Wrinkled and Tall
1/16 will look Wrinkled and Short
P = purple
p= white
T= tall
t = short
PpTt
X
PpTt
9/16 will look Purple and Tall
3/16 will look Purple and Short
3/16 will look White and Tall
1/16 will look White and Short
DIFFERENT PATTERNS FOR HOMOZYGOUS AND HETEROZYGOUS CROSSES:
Rhett and Scarlett are expecting a baby. Rhett’s rich uncle has promised them
$1 million if their baby has blue eyes and is a boy to carry on the family name.
In humans males have Xy alleles and females have XX alleles.
Brown eyes (B) are dominant over blue eyes (b).
Rhett has brown eyes. Scarlett has blue eyes.
Fill in the Punnett square with Rhett and Scarlett’s possible gametes.
Rhett’s Genotype
BbXy
Possible gametes _BX__ _bX_ _By_ _by_
Scarlett’s Genotype
bbXX
_bX
What genotype does a baby need to be a blue eyed boy? _bbXy___________
(and get the $1 million)
Use a Punnett square to show the possible genotypes for their baby.
bX
BX
bX
By
by
__1/4_ Brown eyed boys
BbXX
bbXX
BbXy
bbXy
__1/4_ Brown eyed girls
__1/4_ Blue eyed girls
__1/4_ Blue eyed boys
What is the probability they
will have a BLUE-EYED BOY and get the $1 million?
__25% or 1/4______
Why does this cross not follow the 9:3:3:1 pattern for DIHYBRID (2 gene) crosses?
Both parents have to be dihybrids for a dihybrid cross. Since Scarlett is homozygous for her b’s and X’s, she’s
not a dihybrid.
Punnett Square practice problems obtained from Cheryl Stover (Thanks, Cheryl!)