Name:______________________________
Date:_______________ Period:__________
Dihybrid Crosses
SHOW YOUR WORK!!!
In llamas, floppy ears are dominant to pointy ears.
Also in llamas, bowlegs are recessive.
1. Develop a "key” showing the letters for the two
traits. (Each trait should have a different letter).
Show the phenotypes of your letters too. (Ex: FF =
floppy ears; LL = normal legs)
2. A llama with floppy ears (Ff) and bowlegs is
crossed with one that is heterozygous for both
traits. Show the genotypes of these two parents
3. Draw a Punnett square showing the resulting
offspring.
4. Show the ratios of the resulting phenotypes, use
fractions.
5. A llama that has pointy ears and bowlegs is
crossed with one that is homozygous dominant for
both traits. Show the genotypes of the parents.
6. Draw a Punnett square showing the resulting
offspring.
7. Show the ratios of the resulting phenotypes, use
fractions.
8. A llama that is heterozygous for both traits is
crossed with another llama that is heterozygous for
both traits. Show the genotypes of the two parents.
9. Draw a Punnett square showing the resulting
offspring.
10. Show the ratios of the resulting phenotypes, use
fractions.
Bikini Bottom – Dihybrid Practice
(Adapted from http://sciencespot.net/Media/gen_spbobdihybird.pdf)
Use the information below to solve the following problems:
1. Pants: Squarepants are dominant to roundpants.
2. Body: Yellow body is dominant to blue body.
3. Eyes: Oval eyes are recessive to round eyes.
4. Nose: Stubby nose is recessive to long nose.
Determine the following the genotype for each one using the information above:
1. Heterozygous eyes, homozygous recessive body ________
2. Heterozygous eye shape, homozygous dominant pants ________
3. Homozygous recessive pants, heterozygous nose ________
SpongeBob’s aunt, who is a roundpants, has a cute stubby nose. She has finally found the sponge of her
dreams and is ready to settle down. Her fiancé always comments on how adorable her nose is (he says it
reminds him of his mother’s – aww, how sweet!). They wonder what the chances are of that trait being
passed on. Her fiancé is homozygous dominant for pants and nose.
4. Identify the genotypes of the aunt and her fiancé.
Aunt – Homozygous recessive pants, homozygous recessive nose = ________
Fiancé – Homozygous dominant pants and nose = ________
5. What are the genotypes of SpongeBob, who is heterozygous for his body color and his pants, and his
wife SpongeSusie, who is blue and has roundpants?
SpongeBob = ________
SpongeSusie = ________
6. Complete the Punnett square based on the information provided in #4-5 and then answer the questions.
For SpongeBob and SpongeSusie, what is the chance of a blue baby? ________
For SpongeBob and SpongeSusie, what is the chance of a squarepants? ________
For SpongeBob and SpongeSusie, what is the chance of a blue squarepants? ________
For SpongeBob and SpongeSusie, what is the chance of a homozygous recessive for both traits? _____
7. In starfish, pink body color is dominant to orange, and thick eyebrows are dominant over thin ones.
Patrick, who is heterozygous for body color but homozygous dominant for eyebrows, has met Patti, who is
recessive for both traits.
What is Patti’s phenotype? _______________________________
8. Before Patrick commits to this relationship, he would like to guarantee that his offspring would have his
thick eyebrows. (He thinks they make him smarter!) Complete the Punnett square for Patti and Patrick to
find out which will have thick eyebrows and what body color they will have.
While Squidward’s family boasts about being a purebred line for dominant Squidward Traits:
light blue skin color, they are also purebred for a less distinguished trait: the recessive trait of baldness.
Lack of hair causes Squidward some self-esteem issues that he does not want his children to face. As such,
Squidward is homozygous dominant for skin color and homozygous recessive for hair. In this case, blue
skin is dominant to green and baldness is recessive to hair.
10. Use the information above to complete the Punnett square below as Squidward mates with Octavia, a
green squid (homozygous recessive) and heterozygous for hair and then answer the questions.
For which traits, if any, is it possible for their offspring to be homozygous dominant or recessive?
What is the probability of their children being heterozygous for both traits? ________
Dihybrid Crosses
(Adapted from www.biologycorner.com and http://www.horton.ednet.ns.ca/staff/selig/handouts/bio12/mengenetics/dihybridprob.pdf)
Important Information: In llamas, floppy ears are dominant to pointy ears. Also in llamas, bowlegs are recessive.
1. Develop a "key” showing the letters for the two traits. (Each trait should have a different letter). Show the
phenotypes of your letters too. (Ex: FF = floppy ears; LL = normal legs)
2. A llama with floppy ears (Ff) and bowlegs is crossed with one that is heterozygous for both traits. Show the
genotypes of these two parents and draw a Punnett square showing the resulting offspring. Also, show the ratios
of the resulting phenotypes using fractions.
3. A llama that has pointy ears and bowlegs is crossed with one that is homozygous dominant for both traits.
Show the genotypes of the parents and draw a Punnett square showing the resulting offspring. Also, show the
ratios of the resulting phenotypes using fractions.
4. A llama that is heterozygous for both traits is crossed with another llama that is heterozygous for both traits.
Show the genotypes of the two parents and then draw a Punnett square showing the resulting offspring.
5. In guinea pigs black hair color is dominant to white and short hair is dominant to long. Cross a homozygous
short haired white guinea pig with a homozygous long haired black guinea pig. What are the phenotype and
genotype ratios of the F1 and F2 generations? What are the phenotypes of the F2 generation?
6. In horses, black coats and trotting gait are dominant while the recessive alleles are white and pacing gait. If the
male is homozygous for both dominant traits, what is the genotype of the male ? Cross the homozygous male with
the homozygous recessive female. What are the phenotypes and their ratio in the F1 and F2 generations?
Challenge Questions
7. In snapdragons, the inheritance of flower color and size of leaves are examples of codominance. When red
flowered plants are crossed with white, the result is pink. Similarly, when plants with broad leaves are crossed
with plants having narrow leaves, the offspring have intermediate leaves. Cross a homozygous red-flowered,
broad- leaved plant with a homozygous white-flowered, narrow-leaved plant. What kinds of offspring are
produced in the F1 generation? What are the phenotypes and their ratio in the F2 generation?
8. If a pure variety of peas showing the dominant characteristics tall, axial flower position and blue flowers is
crossed with a variety showing the recessive characters dwarf, terminal flower position and white flowers and the
resulting trihybrids are allowed to self-fertilize, what is the expected visible ratio among the offspring of both
generations ? What are the phenotypes of both generations?
9. Within tribble (a fictional space creature) populations, coat texture (stiff bristles verses soft short fine hair) and
toe type (clawed verses no claws) are autosomal genes. As a geneticist, you are doing the following cross: male
parental phenotype is soft, short fine hair and no toe claws; female phenotype is stiff bristles and clawed toes. In
looking at the offspring of these matings, you find that all F1 are phenotypically stiff bristled and have clawed
toes. Were the parents or homozygous? Which are dominant alleles? If you now mate males to females within the
F1 generation, what would you expect the phenotype ratio to be?