Chapter 3 Branched Tutorial: Working a Dihybrid Cross

Problem Statement

In cucumbers, dull fruit (D) is dominant to glossy fruit (d), and orange fruit (R) is dominant to cream (r) fruit. The gene that codes for dull versus glossy assorts independently from the gene that codes for orange versus cream. A plant that has dull and orange fruits is crossed to a plant that has dull and cream fruits. The cross produces 38 plants with dull and orange fruits, 38 plants with dull and cream fruits, 18 plants with glossy and orange fruits, and 18 plants with glossy and cream fruits. Give the genotypes of the parents and offspring of the cross.

Note: Your answers need to be placed into the chart below in the order that the parents and progeny are presented in the Problem Statement.

Question

Generation Genotypes
P ×
F1
2
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2
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Step 1: Understand the problem and what you need to know

Question

1. What information is the problem asking you to provide?

A.
B.
C.
D.

2
Correct.
Incorrect.

Instant TA

Read the question carefully. After providing some information about the traits and genes that code for them, the problem asks you to provide some specific information.

Step 2: Identify the phenotypes of parents and offspring

Question

1. Outline the phenotypes of the parents and offspring by choosing from the dropdown menus below.

Note: Your answers need to be placed into the chart below in the order that the parents and progeny are presented in the Problem Statement.

Generation Phenotypes
P ×
F1 38
38
18
18
2
Correct.
Incorrect. Reread the problem statement and try again.
Incorrect.

Instant TA

Reread the problem statement. The information needed to select the phenotypes of parents and offspring of the cross is provided for you. Remember that your answers need to be placed into the chart in the order that the parents and progeny are presented in the question.

Step 3: Assigning symbols and the nature of dominance

Question

1. Give the single letter that should be used as an allelic symbol for each trait:

Texture
dull
glossy
Color
orange
cream
2
Correct.
At least one of your answers is incorrect. Try again.

Step 4: Fill in what you know about the parental generation

Now determine what you know about the allelic symbols for the genotypes of the parents, using only what you know from the phenotypes given in the question (not the progeny) to guide you. Use an underscore (_) to indicate any alleles you feel you can not ascertain from the phenotypes.

Question

1. On the basis of its phenotype, which is the correct genotype for the dull, orange parent?

A.
B.
C.
D.

2
Correct.
Incorrect.

Instant TA

Some parts of the genotype can be determined from the phenotype alone. Dull fruit (D) is dominant to glossy fruit (d) and orange fruit (R) is dominant to cream fruit (r).

Step 5: Fill in what you know about the progeny

Now determine what you know about the allelic symbols for the genotypes of the progeny. Use an underscore (_) to indicate any genes you can not ascertain from the phenotypes.

Question

1. On the basis of its phenotype, which is the correct genotype for the glossy, cream offspring?

A.
B.
C.
D.

2
Correct.
Incorrect.

Instant TA

Dull fruit (D) is dominant to glossy fruit (d) and orange fruit (R) is dominant to cream fruit (r). Individuals that possess a recessive trait must carry two alleles for the recessive trait.

Step 6: Separate the cross into two single-locus crosses: part 1

1. The next step in solving the problem is to separate the cross into two single-locus crosses, looking at the inheritance of each trait by itself. Let's start with the texture characteristic.

Question

Generation Genotypes
P (dull) × (dull)
F1 38 dull
38 dull
18 glossy
18 glossy
2
Correct.
Incorrect.

Instant TA

You've already shown that you know this information. Review your work on past steps if necessary.

Step 6: Separate the cross into two single-locus crosses: part 2

Now let's consider the color characteristic. First assemble the relevant information.

Question

1. In the table below fill in again what we know about the color alleles for parents and progeny based solely on the information given directly in the question.

Generation Genotypes
P (orange) × (cream)
F1 38 orange
38 cream
18 orange
18 cream
2
Correct.
Incorrect.

Instant TA

You've already shown that you know this information. Review your work on past steps if necessary.

Step 7: Solving the Problem

1. Now put it all together and try filling in the whole table again:

Note: Your answers need to be placed into the chart below in the order that the parents and progeny are presented in the Problem Statement.

Question

Generation Genotypes
P (dull, orange) × (dull, cream)
F1 dull, orange
dull, cream
glossy, orange
glossy, cream
2
Great job!
At least one of your answers is incorrect. Try again.
Incorrect. Please review Chapter 3 and try the Branched Tutorial again.
Notes: