Transcript How to make a punnett square

How to make a
punnett square
A step by step method
What is a punnett square?
A
punnett square is a diagram used to try
to predict the outcome of a cross
between 2 parents.
 It does not tell us what will happen, but it
does tell us the likelihood that something
will happen.
Monohybrid crosses
 These
are crosses that only look at a single
trait
 Ex: hair color, eye color, albinism
 Ex: What are the chances that my baby
will have brown eyes?
Step 1
 Draw
a box and divide it into 4 squares.
These squares represent the possible offspring
Step 2
 Determine
the
genotypes of the
parents. ____x_____
 Place the alleles for the
genotypes of the
parents on the sides
and top of the square.
 As a general rule, we
put the dad on the top
and the mom on the
side.
R
r
r
R
Step 3
 Now
you multiply
the sides with the
top to get the
genotype of the 4
offspring boxes.
R
R
r
Rr
Rr
r
Rr
Rr
Step 4
 Now
you can see
what the genotypes
of the offspring
would be.
r
 In this case there is
a 100% chance of
the offspring being
r
heterozygous for
the trait because all
4 out of 4 boxes are
capital, lower case.
R
R
Rr
Rr
Rr
Rr
Ratios
 Genotypic
 Ask



your self:
How many homozygous dominants?
How many heterozygous?
How many homozygous recessives?
 Phenotypic
 Ask


yourself:
How many dominant phenotypes?
How many recessive phenotypes?
Let’s Practice
 Homozygous
AA ____
HO
Bb ____
HE
HE
Cc ____
HE
Dd ____
(HO) or Heterozygous (HE)
Ee ____
HE
ff ____
HO
HO
GG ____
HO
HH ____
Determine Phenotype
Purple flowers are
dominant to white flowers
Brown eyes are dominant
to blue eyes
Purple
PP _____________
Purple
Pp _____________
White
pp _____________
Brown
BB ____________
Brown
Bb ____________
Blue
bb ____________
For each phenotype list the
genotype
Straight hair is dominant to
curly.
Pointed heads are dominant
to round heads.
SS
PP
____________
straight ____________
pointed
____________
straight ____________
pointed
Ss
Pp
ss
pp
____________
curly
____________
round
Problem #1
Step 1
 In
Draw punnett square
pea plants, spherical
seeds (S) are dominant to
dented seeds (s). In a
genetic cross of two plants
that are heterozygous for
the seed shape trait, what
fraction of the offspring
should have spherical
seeds?
Problem #1
Determine the genotype of parents, and
place alleles on punnett square
Ss
Ss
 In pea plants,
 ________
x ________
spherical seeds (S) are
dominant to dented
S
s
seeds (s). In a genetic
cross of two plants
that are heterozygous
for the seed shape
trait, what fraction of
the offspring should
have spherical seeds?
S
s
Step 2
Problem #1
pea plants,
spherical seeds (S) are
dominant to dented
seeds (s). In a genetic
cross of two plants
that are heterozygous
for the seed shape
trait, what fraction of
the offspring should
have spherical seeds?
Ss
 ________
Ss
x ________
S
s
s
 In
Multiply sides to get possible offspring
Ss
ss
S
Step 3
SS
Ss
Problem #1
S
s
Interpret the possible offspring
Step 4
 In pea plants, spherical
Ss
Ss
 ________
x ________
seeds (S) are dominant
to dented seeds (s). In a
S
s
genetic cross of two
plants that are
heterozygous for the
Ss
ss
seed shape trait, what
fraction of the offspring
should have spherical
SS
Ss
seeds? 3/4
Problem #2
3 Interpret
Multiply
Determine
Parent
genotypes
Draw
punnett
square
Step 1
42
the
possible
offspring
SquarePants
rr
Rr
x ________
recently met SpongeSusie  ________
Roundpants at a dance.
R
r
SpongeBob is heterozygous
for his square shape, but
SpongeSusie is round
Rr
rr
(recessive). What is the ratio
of round to square pants?
r
r
 SpongeBob
2:2
Rr
rr
Problem #3
b
b
Step
Parent
genotypes
3
Multiply
4 Determine
Interpret
the
possible
offspring
Step 2
1
Draw
punnett
square
 Squidward is purebred for
BB
bb
 ________
x ________
light blue skin, which is the
B
B
dominant trait for body color.
He recently married a nice
Bb
Bb
girl who has light green skin,
which is a recessive trait.
Create a Punnett square to
show the possibilities that
Bb
Bb
would result if Squidward and
his new bride had children.
 What percentage of
0%
Squidward’s offspring could
be green?
Dihybrid crosses
 Dihybrid
crosses are punnett squares used
to predict the probability of an offspring
having 2 traits at the same time.
 Ex: What are the chances of my baby
having brown eyes AND blond hair.
Step 1
 Draw
a box and
divide it into 16
squares.
Step 2
 Determine
the
genotypes of the
parents
 Ex: cross two pea
plants that are
heterozygous for
yellow peas and round
peas.
 Yellow is dominant to
green and round is
dominant to wrinkled.
 YyRr x YyRr
Step 3
 Determine
all of the
possible gamete
combinations for each
parent by using the
F.O.I.L. or Gremlin
method
 FOIL= first, outside, inside
last
 Ex: YyRr

First- YR
 Outside-
Yr
 Inside- yR
 Last- yr
Gremlin
YyRr
Step 4
 Write
all of the
YR
possible combinations
of alleles on the sides YR
and top of the
Yr
punnett square.
 YR
 Yr
 yR
 yr
yR
yr
Yr
yR
yr
Step 5
 Go
through the
results and
determine what the
phenotype of each
offspring would be
Yr
yR
yr
YYRR
YYRr
YyRR
YyRr
Yellow
round
Yellow,
round
Yellow,
round
Yellow,
round
YYRr
YYrr
YyRr
Yyrr
Yellow,
round
Yellow,w
rinkled
Yellow,
round
Yellow,
wrinkled
YyRR
YyRr
yyRR
yyRr
Yellow,
round
Yellow,
round
Green,
round
Green,
round
YyRr
Yyrr
yyRr
Yyrr
Yellow,
round
Yellow,
wrinkled
Green,
round
Green,
wrinkled
YR
YR
Yr
yR
yr
Step 6
 Figure
out the
phenotypic ratio or
answer whatever
question they ask
you.
 9:3:3:1
 Example:
what are
the chances of
having a yellow
and wrinkled pea?
 3/16
Yr
yR
yr
YYRR
YYRr
YyRR
YyRr
Yellow
round
Yellow,
round
Yellow,
round
Yellow,
round
YYRr
YYrr
YyRr
Yyrr
Yellow,
round
Yellow,w
rinkled
Yellow,
round
Yellow,
wrinkled
YyRR
YyRr
yyRR
yyRr
Yellow,
round
Yellow,
round
Green,
round
Green,
round
YyRr
Yyrr
yyRr
Yyrr
Yellow,
round
Yellow,
wrinkled
Green,
round
Green,
wrinkled
YR
YR
Yr
yR
yr
Let’s Practice
 Determine
the gametes for the following cross:
heterozygous tall plant with heterozygous yellow
seeds with another of the same genes. Tall and
yellow are dominant
F.O.I.L
TtYy
First-TY
Outside- Ty
Inside- tY
Last- ty
Gremlin
TtYy
Problem #4
3
and
Analyze
4punnett
Determine
results
gametes and place on square
15
Draw
square
2 Answer
Determine
genotypes
Step 6
question(s)
Suppose the alpha male and
alpha female of a wolf pack
nnbb x ________
NnBb
 ________
are black with blue eyes and
nb
nb
nb nb
normal colored with brown
NnBb NnBb
NnBb
NnBb
eyes, respectively. Assume
normal,
normal,
normal,
normal,
further that normal coat color
brown
brown
brown Bb brown
Bb
(N) is dominant to black (n)
Nnbb
Nnbb
Nnbb
Nnbb
normal,
normal,
normal,
normal,
and brown eyes (B) are
blue
blue
blue
blue
dominant to blue (b). The
nnBb
nnBb
nnBb
nnBb
Bb
Bb
black,
black,
black,
black,
female is also heterozygous for
brown
brown
brown
brown
both traits.
nnbb
nnbb
nnbb
nnbb
What fraction of the offspring
black,
black,
black,
black,
blue
blue
blue
blue
could have the following
genotypes?

nb
nB
Nb
NB

NNBB: 0/16 NnBb: 4/16 nnbb: 4/16