Download punnett square

Monohybrid Cross
§ Crossing two
organisms in
order to
compare one
trait.
What is a PUNNETT SQUARE?
•  A tool to predict the probability of
certain traits in offspring that shows
the different ways alleles can combine
•  A chart that shows all the possible
combinations of alleles that can result
when certain genes are crossed
What is a PUNNETT SQUARE?
•  Letters stand for dominant and
recessive alleles
•  An uppercase letter stands for a
dominant allele
•  Lowercase letters stand for recessive
alleles
Using a PUNNETT SQUARE
To set up a Punnett square, draw a large
square, and then divide it into 4 equal
sections (also squares). It should look
something like this:
Using a PUNNETT SQUARE
Now you need two parents to cross, you
must know the genotype of each parent
For example, a red flower (genotype Rr)
and a white flower (genotype rr).
Rr x rr
Using a PUNNETT SQUARE
Place one of the parents on top, and one
on the left. You should get a something
similar to this:
Using a PUNNETT SQUARE
Finally, take each letter in each column and
combine it with each letter from each row in
the corresponding square. You should now
have a picture close to this:
3.
Using a PUNNETT SQUARE
•  The possible genotype combinations of
the offspring are:
Rr, Rr, rr, and rr
•  We now know that the probability of the
offspring having a red phenotype is 2/4
or 50% or a white phenotype 2/4 or
50%.
Punnett Square Practice 4.
G
g
G
g Gg gg
GG Gg
The parents in this cross
are _____________
Heterozygous
Homozygous
Heterozygous
If G is dominant for green pods and g is recessive for
yellow pods, what percentage of the offspring will have
green pods? _______%
75
5.
B b
B
b
The genotype of the
offspring in the red box is
_______
bb
The offspring in the red box is
homozygous
heterozygous
homozygous recessive
6. In guinea pigs black fur (B) is dominant over brown fur (b).
The Punnett square for a cross between a HETEROZYGOUS
black guinea pig and a PURE brown guinea pig would look
like:
B B
B b
B b
B b
B
b
b
B
b
b
b
B
This is the
Correct setup
Heterozygous = Bb
Pure brown = bb
homozygous
Another name for pure is _________________
7.
r
r
R
r
Rr
rr
Rr
rr
Red throats (R) are
dominant over white (r)
throats in Goonie birds.
Make a cross between a
PURE RECESSIVE and a
HETEROZYGOUS Gooney
Bird.
What are the possible phenotypes of
their offspring? (% and color)
50% red throats
50% white throats
8.
B
b
B
BB
Bb
b
Bb
bb
What are the possible phenotypes
of their offspring? (% and color)
75 % black eyes
25% red eyes
Black eyes (B) are
dominant over red
eyes (b) in rats.
Make a cross between
two HETEROZYGOUS
rats.
Which of the following genotypes could be
from a HETEROZYGOUS organism?
TT
Rr
Ww
Rr
Ww
bb
XX
Ss
Ss
9.
What kind of cross is this?
Pure dominant X pure recessive
Heterozygous X heterozygous
Heterozygous X homozygous
Hybrid recessive X hybrid pure
Heterozygous X Homozygous
hybrid
Another name for heterozygous is _______________
10.
T
t
t
Tt
Tt
T
Tt
Tt
What is the probability the offspring
will have straight tails?
In Pigs curly tails (T)
are dominant over
straight tails (t).
Make a cross between
a HOMOZYGOUS
DOMINANT and a
HOMOZYGOUS
RECESSIVE Pig.
0%
All will be Curly tailed (Tt)
Which of the following genotypes could be
from a HOMOZYGOUS RECESSIVE
organism?
TT
bb
bb
Rr
Ww
tt
tt
XX
aa
aa
11.
A a
A
a
The genotype of the
offspring in the red box is
_______
homozygous
heterozygous
heterozygous
What percentage of the offspring from this cross will
show the dominant characteristic?
¾ (75%)
12.
G g
G
g
GG Gg
gg
G is dominant for green pea pods.
g is recessive for yellow pea pods.
What is the genotype of the
offspring in the blue box?
Gg
What is the phenotype of the offspring in the
blue box?
Green pea pods
13.
P
P
p
Pp
Pp
p
Pp
Pp
What will the offspring be like?
(% and color)
Purple (P)is the
dominant color for
monsters. Yellow is
recessive (p).
Make a cross between
a HOMOZYGOUS
purple and a yellow
monster.
100% purple
What genotype would a PURPLE dad have to be to
make a yellow monster baby with a Purple (Pp)
mom monster? – Remember Purple is DOMINANT
P
?
?
p
Baby is pp
Dad is Pp
Dad needs to have:
a little p to give one to the baby
a big P to be purple himself
Which of the following is NOT TRUE?
T
Genotype determines phenotype
T
Alleles are different forms of the same gene.
F
Genotype is the way the genes make you look.
T Organisms with different genotypes
can have the same phenotype.
Tt and TT both look tall