Go through the following slides and complete tasks on how to use punnett
squares to predict genetic outcomes of offspring. Read each slide carefully
and complete tasks.
Probability can be used to predict the results of genetic crosses. In
other words you can figure out what fraction or percentage of the
offspring will have the trait.
To help figure this out punnett squares are used. A punnett square is a
special chart that is used to show the possible gene combinations in a
cross between two organisms.
Before you can create punnett squares you must understand
some of the key terms. Click on the button below to go to the
next slide and view the definitions.
Click on sound icon
Two different genes make up the trait. Click on
the colored word hybrid for the example to
appear.
The hybrid is circled because it has an
Upper and lower case letter or not the
same throughout.
TT
Tt
tt
The genes are the same for the trait. Click
on the blue word purebred for the example
to appear.
The purebreds are circled because they
have the same letters.
TT
Tt
tt
This is the actual gene makeup of the organism. Click
on the purple word genotype for an example. Click on
the sound icon under genotype for an explanation
The letters that makeup the trait. The following are
examples. If red roses are dominant over white then
the following could be possible genotypes.
T = Red Rose
t = White Rose
The possible genotypes are circled
TT
Tt
tt
What the physical appearance of the trait or
organism looks like. Click on the orange word
phenotype to view the example. Click on the
sound icon under phenotype for an explanation.
The rose could be red or
white, so the phenotype will
be red or white. If the
genotype is TT or Tt the rose
will be red. If the genotype is
tt the rose will be white.
Write the correct phenotype for the following examples
Click on the gray box and type in
what color fur each hamster has
if black fur is dominant over
white fur.
B – Black fur
b – White fur
bb -
White Fur
BB -
Black Fur
Bb -
Black Fur
Once you have typed in
your answers click on the
answer button below and
they will appear.
Write the correct genotype for the following examples
Click on the gray box and type in
what the gene makeup would be
for each hamster. Black fur is
dominant over white fur.
B – Black fur
b – White fur
Purebred Black Fur -
BB
White Fur -
bb
Hybrid Black Fur -
Bb
Once you have typed in
your answers click on the
answer button below and
they will appear.
Now that you understand the terms we will come back to the
punnett squares. The first part of creating a punnett square
is choosing the letter that will represent the genes. The only
rule I have is that the letters you choose have a different
upper and lower case. Click on both the good and bad
example below.
A
a
Different upper
case and lower
case
S
s
Same upper
case and lower
case
Click on the boxes below that would be good letters to choose to
represent the genes that will be used for the punnett square. If not sure
go back to the previous slide and look at the good and bad examples.
Kk
Hh
If you have the following boxes
checked then you are ready to
move on.
Gg
Dd
Gg
Ll
Ll
Bb
Hh
Cc
Rr
Dd
Bb
Oo
Vv
Once you have typed in
your answers click on the
answer button below and
they will appear.
Rr
Now that you know how to pick the letter the next part
is to figure out which is dominant and which is
recessive. Remember dominant is the gene that hides
the weaker trait whenever it is present. The dominant
trait is always the capital letter. The recessive trait is
always the lower case letter. Now click the word
example. After you read through the example click on
the sound icon, near the bottom, to listen to an
explanation.
In pea plants, round seeds are dominant
over wrinkled seeds. Pick a letter to
represent dominant and recessive genes.
T = Round Seeds
t = Wrinkled Seeds
I chose the letter T to represent the
dominant and recessive genes. Round is
dominant so it is the capital T. The lower
case t is wrinkled because it is recessive.
Try these out.
Orange tulips are dominant over white tulips. Pick a letter to represent dominant
and recessive. Write the letter and what it stands for in the gray box below. Click
on answer to see if you are correct.
Letters may be different, but
make sure capital and lower
case are different.
B = Orange Tulips
b = White Tulips
Brown eyes are dominant over blue eyes in huskies. Pick a letter to represent
dominant and recessive. Write the letter and what it stands for in the gray box
below. Click on answer to see if you are correct
Letters may be different, but
make sure capital and lower
case are different.
H = Brown eyes
h = Blue eyes
The second part to creating a punnett square is figuring out the genotypes of the
parents. To do this you have to pay close attention to what the question is asking
you to cross. Below is an example of a question. I underlined the key words that
can help you determine the parents genotype. Click on the sound icon for
explanation.
In pea plants, round seeds are dominant over wrinkled seeds. Predict the
genotypes and phenotypes of a cross between two hybrid round-seeded pea
plants.
Since they are both hybrid round that means their letters are different.
The first thing you do is pick your letters, like on previous slide, and then
you show the cross. The cross is shown by the X.
R = round
r = wrinkled
Parent 1
Rr X Rr
Hybrid round
Hybrid round
Parent 2
Try these!! Write the dominant/recessive letter and then the cross between
the parents in the gray box under the question. Click on the answer to see if
you were right. The letter you chose may be different, but that will not
matter. Look at previous slide if you are not sure.
In mice black fur is dominant over white fur. Predict the genotype and
phenotype of a cross between a purebred black furred mouse with a
purebred white furred mouse.
B = Black Fur
b = White Fur
BB X bb
Purebred Black fur
Purebred White fur
If brown eyes are dominant over blue eyes in Huskies predict the genotype and
phenotype of a cross beween a hybrid brown eyed husky and a blue eyed
husky.
B = Brown eyes
b = Blue eyes
Bb X bb
Hybrid brown eyed
Blue eyes
Now that you have the cross you can create the punnett square. So far you have picked the
letter, labeled the dominant/recessive, and found the cross. Now we will label and fill in the
punnett square to figure out what possibilities are for the offspring. Click on the word problem
to start. Next click step 1 and then step 2.
In mice black fur is dominant over white fur. Predict the
genotype and phenotype of a cross between a purebred
black furred mouse with a purebred white furred mouse.
Step 1 Click Here
B = Black Fur
b = White Fur
BB X bb
Step 2 Click Here
1st take one of the parents letters and write
them along the left side of the boxes. I have
circled the BB for parent 1 and moved them
over to the box
b
So far you have
completed this.
2nd take the other
parent and write their
genotype letters
along the top of the
boxes.
B
B
b
Below is what you have so far and how to fill in the chart.
Keep clicking on the word cross until the punnett square is
filled in. This shows you how to fill in a punnett square. Pay
close attention.
Parent 2
B = Black Fur
b = White Fur
b
BB X bb
b
B
Bb
Bb
B
Bb
Bb
Parent 1
Click on sound icon
to hear explanation
Possible genotypes and phenotypes of
offspring.
See if you can fill in the letters to the punnett
square below correctly. Click on the word
answer to see if you are correct.
Parent 2
t
t
Tt X tt
T
Parent 1
t
Parent 2
t
t
T
Tt
Tt
t
tt
tt
Parent 1
The last part of to creating a punnett square is finding the genotype and phenotype of the possible
offspring. Below is an example of gene makeup and appearance of parents and possible offspring.
To get the genotype you look at the letters of the possible offspring. In this case all of the offspring
have Bb, so they are all hybrid. The phenotype is the color of their fur and in this case all of the
offspring will have black fur, since they are all hybrid and black fur is dominant. All of their offspring
will carry the trait for white fur, but it will not show through. Click on the sound icon at the bottom for
explanation.
In mice black fur is dominant over white fur. Predict the
genotype and phenotype of a cross between a purebred
black furred mouse with a purebred white furred
mouse.
B = Black Fur
b = White Fur
BB X bb
Parents
b
b
B
Bb
Bb
B
Bb
Bb
Genotype
100% Hybrid Bb
Phenotype
100% Black Fur
Possible Offspring
Find the genotype and phenotype for the following problem. Now
remember to look at the offspring to determine the genotype and
phenotype. There are 4 boxes so each box stands for 25%.
Parent 2
R = round
R
r = wrinkled
r
Rr X Rr
Genotype
R
RR
Rr
r
Rr
rr
Parent 1
25% Purebred RR
50% Hybrid Rr
25% Purebred rr
Phenotype
75% Round
25% Wrinkled
Below is an exact example of how to set up a punnett square. When you are
writing it on your paper it should be set up like this. The punnett square is always
on the right and the information is always on the left. I have numbered the steps 14 so you know the order to solve the problem. Click on each black number in order
to see the explanation. Last click on sound icon near the bottom to hear
explanation.
In mice black fur is dominant over white fur. Predict the genotype and phenotype of
a cross between a hybrid black furred mouse with a purebred white furred mouse.
B = Black Fur
b = White Fur
Bb X bb
2
Genotype
4
50% Hybrid Bb
50% Purebred bb
1
1. Pick you letters
and make sure the
dominat is capital
3
50% white fur
b
2. Write the cross of
the parents
3. Create the punnett
square.
B
Bb
Bb
4. Find the genotype
and phenotype of
the offspring using
the punnett square.
b
bb
bb
Phenotype
50% black fur
b
Complete the problem below. Click on the sound icon, near the bottom, for a quick
overview on the steps. Do not click on the answer until you have completed the entire
problem. Remember to follow the steps from the previous slide. The letter you chose
might be different then mine, but as long as you follow the rule it doesn’t matter.
In roses the color red is dominant over white . Predict the genotype and phenotype
of a cross between two hybrid red roses.
R = Red
r = White
Rr x Rr
Genotype
25% Purebred RR
50% Hybrid Rr
25% Purebred rr
R
Phenotype
75% Red
r
R
RR
Rr
r
Rr
rr
25% White
Complete the following problem on a sheet of paper. Click on the
sound icon for an explanation. Make sure you use all four steps to
answer the problem. Set up your problem so that it looks like the
punnett on the previous slide. Bring it up to me to correct.
If brown eyes are dominant over blue eyes in huskies predict the
genotype and phenotype of a cross between a hybrid brown eyed and a
purebred blue eyed.