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 genes coding for dull and glossy assort independently from the genes coding for orange and cream. A plant that has dull and orange fruits is crossed to a plant that has dull and cream fruits. The cross produces 3⁄8 plants with dull and orange fruits, 3⁄8 plants with dull and cream fruits, 1⁄8 plants with glossy and orange fruits, and 1⁄8 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 given in the question.

Question

Generation Genotypes
P ×
↓
F1
2
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2
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Understand the problem and what you need to know

Question

What information is the problem asking you to provide?

A.
B.
C.
D.
2
Correct.
That's not's quite right. 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. Try again.
Incorrect. The only thing the problem is asking you to explicitly provide is the genotypes of the parents and the progeny. The problem does not ask for phenotypes, phenotypic ratios, or genotypic ratios of the progeny.

Identify the phenotypes of parents and offspring

Question

Outline the phenotypes of the parents and offspring by choosing from the drop-down menus below.

Note: Your answers must appear in the order given in the problem statement above to be considered correct.

Generation Phenotypes
P ×
↓
F1 3⁄8
3⁄8
1⁄8
1⁄8
2
Correct.
Read the problem. The information needed to select the phenotypes of parents and offspring of the cross is provided in the problem. Remember, your answers need to appear in the order given in the question.
Incorrect.

Assigning symbols and the nature of dominance

Question

Give the single letter that should be used as an allelic symbols for each trait:

Texture
dull
glossy
Color
orange
cream
2
Correct.
Read the problem. The one-letter symbols used for each allele are given there.
Incorrect.

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 genes you feel you can not ascertain from the phenotypes.

Question

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

A.
B.
C.
D.
2
Correct.
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). Try again.
Incorrect.

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

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

A.
B.
C.
D.
2
Correct.
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. Try again.
Incorrect.

Separate the cross into two single-locus crosses: Texture

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

First assemble the relevant information. In the table below fill in again what we know about the texture alleles for parents and progeny based solely on the information given directly in the question:

Generation Genotypes
P (dull) × (dull)
↓
F1 3⁄8 dull
3⁄8 dull
1⁄8 glossy
1⁄8 glossy
2
Correct.
You've already shown that you know this information. Review your work on past steps if necessary, then try again.
Incorrect. See correct answers above.

Separate the cross into two single-locus crosses: Color

Now let's consider the color characteristic.

Question

First assemble the relevant information. 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 3⁄8 orange
3⁄8 cream
1⁄8 orange
1⁄8 cream
2
Correct.
You've already shown that you know this information. Review your work on past steps if necessary, then try again.
Incorrect. See correct answers above.

Put It All Together

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

Question

Generation Genotypes
P (dull, orange) × (dull, cream)
↓
F1 dull, orange
dull, cream
glossy, orange
glossy, cream
2
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Incorrect. Try reloading the tutorial and going through the individual steps again.
Notes: