Transcript How to make a punnett square ppt

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
S
that are heterozygous
for the seed shape
trait, what fraction of
the offspring should
s
have spherical seeds?
Step 2
Problem #1
Step 3
 In
Multiply sides to get possible offspring
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
SS
Ss
s
Ss
ss
Problem #2
 SpongeBob
SquarePants
ss
Ss
x ________
recently met SpongeSusie  ________
Roundpants at a dance.
S
s
SpongeBob is heterozygous
for his square shape, but
SpongeSusie is round
s
Ss
ss
(recessive). What is the ratio
of round to square pants?
s
Ss
ss
2 Round : 2 Square
Problem #3
 What
is the probability of
Ll
LL
x ________
producing offspring that  ________
have short whiskers from a
L
L
cross of two long-whiskered
seals, one that is
homozygous dominant and L
LL
LL
one that is heterozygous?
What is the outcome for
long whiskers and short
l
Ll
Ll
whiskers?
100% Long, 0% Short
Problem #4
 In
pea plants, purple flowers
PP
PP
x ________
are dominant over white  ________
flowers, which are
P
P
recessive. Cross two
homozygous dominant
parents. What is the
P
PP
PP
outcome for this cross
between two homozygous
dominant parents?
P
PP
PP
100% Purple Flowers
Problem #5
 In
pea plants, round peas
RR
Rr
x ________
are dominant and wrinkled ________
peas are recessive. Cross a
R
r
heterozygous parent with a
homozygous round pea
plant. What is the outcome R
RR
Rr
for this cross?
100% Round Pea Plants
R
RR
Rr