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Punnett Square Review
Use the following Punnett square to answer the questions below.
In watermelons, green skin (G) is dominant over striped skin (g). The Punnett square below shows the genetic cross
between a GG watermelon and a Gg watermelon.
G
G
G
GG
GG
g
Gg
X
1.
List the genotype of the homozygous dominant parent watermelon.
2.
What term describes the genotype of the Gg watermelon?
3.
What would be the genotype of the offspring in box X?
4.
What would be the phenotype of the offspring in box X?
5.
What is the probability that the offspring would be homozygous recessive?
6.
What is the probability that the offspring would be green?
7.
The GG and Gg offspring will have the same
8.
List the genotypes of the offspring that will express the dominant trait.
9.
List the genotypes of the offspring that will express the recessive trait.
.
“NORMAL” 1 DOMINANT AND 1 RECESSIVE ALLELE
In humans, the ability to roll your tongue (T) is dominant over the inability to roll your tongue (t). Show the genetic
cross between a homozygous tongue roller and a homozygous non-tongue roller.
1. Make a key.
2. List the parents’ genotypes.
3. Show the Punnett square.
4. List the genotypes of the
offspring.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be able to roll their
tongue?
In fruit flies, the gene for gray body color (G) is dominant over the gene for ebony body color (g). Show the genetic
cross between a homozygous ebony bodied fly and a heterozygous gray fly.
1. Make a key.
3. Show the Punnett square.
2. List the parents’ genotypes.
4. List the genotypes of the
offspring.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be heterozygous?
INCOMPLETE DOMINANCE
In Japanese four o’clocks, red flower color (R) is incompletely dominant to white flower color (W). Show the genetic
cross between two pink plants.
1. Make a key.
3. Show the Punnett square.
2. List the parents’ genotypes.
4. List the genotypes of the
offspring.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be pink?
CODOMINANCE AND MULTIPLE ALLELES
In chickens, black feathers (B) are codominant with white feathers (W). Heterozygotes are speckled. Show the
genetic cross between a white chicken and a black chicken.
1. Make a key.
3. Show the Punnett square.
4. List the genotypes of the
offspring.
2. List the parents’ genotypes.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be black?
In humans, there are three alleles for blood type. Blood types A (I A) and B (IB) are both dominant. Blood type O (i) is
recessive. Show the genetic cross between a woman that is homozygous for blood type O and a man who is
heterozygous for blood type B.
1. Make a key.
3. Show the Punnett square.
4. List the genotypes of the
offspring.
2. List the parents’ genotypes.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be type A?
In humans, there are three alleles for blood type. Blood types A (I A) and B (IB) are both dominant. Blood type O (i) is
recessive. Show the genetic cross between a woman who is homozygous for blood type A and a man who is
heterozygous for blood type A.
1. Make a key.
3. Show the Punnett square.
4. List the genotypes of the
offspring.
2. List the parents’ genotypes.
5. List the phenotypes of the
offspring.
6. What is the probability that the
offspring will be type A?
Standardized Test Prep
A researcher studying fruit flies finds a mutant fly with brown-colored eyes. Almost all fruit
flies in nature have bright red eyes. When the researcher crosses the mutant fly with a normal
red-eyed fly, all the F1 offspring have red eyes. The researcher then crosses two of the F1 redeyed flies and obtains the following results in the F2 generation.
Eye Color in the F2 Generation
Red eyes
37
Brown eyes
14
1.
Calculate What is the ratio of red-eyed flies to brown-eyed flies?
a. 1:1
b. 1:3
c. 3:1
d. 4:1
2. Draw Conclusions The allele for red eyes in fruit flies is
a. dominant over brown eyes.
b. recessive to brown eyes.
c. codominant with the brown-eyed gene.
d. a multiple allele with the brown-eyed gene and others.