Practicing Punnett Squares
Reminders & Review:
For the following cross: TT X tt
Whose genotype listed first (left)?
__________________
Whose genotype listed last (right)?
__________________
The capital letters represent a __________________________ trait.
The lower case letters represent a _______________________ trait.
Where do mom’s genes go on a Punnett square? __________________
Where do dad’s genes go on a Punnett square? ___________________
The gene (letter) combination is called the ________________________.
The physical traits that show make up the _________________________.
In a phenotype ratio you always write the ____________________ trait first.
Use the Punnett squares to predict the genotypic and phenotypic
outcomes of the following crosses:
Problem #1:
Tt X Tt
Height (T = tall; t = short)
Problem #2:
Yy X yy
Pea pods
(Y = yellow; y = green)
homozygous dominant: ______%
homozygous dominant: ______%
homozygous recessive: ______%
homozygous recessive: ______%
heterozygous:
______%
heterozygous:
______%
phenotype ratio:
______
phenotype ratio:
______
Problem #3:
RR X rr
Flower color (R = red; r = white)
Problem #4:
bb X bb
Fur color
(B = black; b = brown)
homozygous dominant: ______%
homozygous dominant: ______%
homozygous recessive: ______%
homozygous recessive: ______%
heterozygous:
______%
heterozygous:
______%
phenotype ratio:
______
phenotype ratio:
______
For each of the following problems, list the genotypes of the parents,
complete a Punnett square and give the phenotype percentages of the
offspring.
5. In garden peas, round seed coats (R) is dominant over
wrinkled seed coats (r). What will the results be of a
cross between a homozygous dominant male and a
homozygous recessive female?
mom: _______ dad: _______
round:
________% wrinkled:
________%
________________________________________________________________
6. In humans, straight toes (S) is dominant over curled
toes (s). What would be the result of a cross between a
homozygous recessive male and a heterozygous female?
mom: _______ dad: _______
straight:
________% curled:
________%
7. In dogs, erect ears (E) is dominate over droopy ears
(e). What are the results if two heterozygous dogs have
a litter of puppies.
mom: _______ dad: _______
erect:
________% droopy:
________%
________________________________________________________________
8. The ability to roll the tongue (R) is determined by a dominant gene while the
recessive gene results in the inability to roll the tongue (r). A man and his
wife can both roll their tongues and are surprised to find that their son
cannot. Explain this by showing the genotypes of all three persons. (Note:
you do not need to do a Punnett Square for this problem).
________________________________________________________________
The following Punnett squares show the results of four different crosses made
with pea plants. In this case, flower color red (R) is dominant over white (r). For
each of the results listed below, write down the number of the Punnett square
that matches.
1.
R
R
2.
r
Rr
Rr
R
r
Rr
Rr
r
R
R
3.
R
r
4.
R
r
RR RR
R
RR
Rr
r
Rr
rr
Rr
r
Rr
rr
r
Rr
rr
Rr
______ a. A red flowered plant was crossed with a white flowered plant. The
results were 126 red flowering plants and 122 white flowered plants.
Which Punnett Square applies?
______ b. A red flowered plant was crossed with a white flowered plant. The
results were 307 red flowering plants and 0 white flowered plants.
Which Punnett Square applies?
______ c. A red flowered plant was crossed with a red flowered plant. The
results were 306 red flowering plants and 110 white flowered plants.
Which Punnett Square applies? ______
______ d. A red flowered plant was crossed with a red flowered plant. The
results were 300 red flowering plants and 0 white flowered plants.
Which Punnett Square applies?
In hamsters, brown fur (B) is dominant over white fur (b). A brown furred male
mates with white furred female and they have three offspring, two of whom are
brown furred and one of whom is white furred. Complete the Punnett square
that illustrates this situation.
If white is recessive, what must the female hamsters genotype be? __________
If the male has brown fur, but has a white furred offspring what must his
genotype be? __________