In data table below, write the proportions of the two phenotypes as displayed

Introduction to Genetics

Introduce yourself to the virtual Genetics lab room to discover how pea plants display Mendelian inheritance patterns.

Gregor Mendel's meticulous work with pea plants allowed him to discover patterns of inheritance in sexually reproducing organisms. In this introductory virtual lab activity, you can simulate some of Mendel’s crosses and data analyses.

Enter the Virtual Bio Lab and select the title of this lab activity from the “Heredity” menu on the whiteboard. You will be taken to the virtual Genetics lab room.

Part A: The Virtual Genetics Lab Room

The virtual Genetics lab room lets you perform virtual crosses between males and females of a variety of model species to determine how different traits are inherited. By default, the pea plant lab environment will appear. In some activities you may be working with human traits, in which case the settings will look like a physician’s office. When working with other animal species, the lab will again look different.

First Generation

Select “Pea Plant” from the Species Selector. In the box on the lower left part of your screen labeled “Experiment Setup,” select “Seed Shape” as the trait to explore.

The Genetics lab lets you set each parent’s genotype for the selected trait and then perform an unlimited number of crosses to determine how a particular trait is passed on to the next generation. The simulation limits the number of offspring per cross to a realistic number for the species in question, however. In the lower left corner of the “Experiment Setup” box, set “Number of Offspring” to 10.

Now, set one parental pea plant’s genotype as homozygous for “Wrinkled” and the other’s genotype as heterozygous. To set a genotype, pull down on each of the dropdown menus below a given parent.

Next, click the “Cross” button. The results of your crosses will be displayed in the “Results” boxes to the right of the experiment setup screen. Under the headings “Parents” and “F₁ Offspring,” you will see the individuals listed using names such as MF1, MF2, and so on. (MF1 means male-female number 1—the first offspring, which has both male and female reproductive organs.) To check the phenotypes of an individual offspring, roll over any of the offspring names. In the window that appears, the phenotype of the offspring is shown in the first of three boxes and described to the left. The phenotypes of the parents are shown in the other two boxes.

In the “By Generation” results panel, you will find the proportional breakdown of the phenotypes displayed by the first (F₁) generation of ten offspring. The values given at the far right side of the horizontal bar graphs (“Round” and “Wrinkled”) tell you what proportions of that generation have a particular phenotype. For example, if 0.70 of offspring are wrinkled, that means 70% are wrinkled.

1. In data table below, write the proportions of the two phenotypes as displayed by the first ten offspring. Then, click the “Cross” button again, to simulate the production of 10 more offspring. Record the new phenotype proportions (for 20 offspring) in the next row. Repeat this process until the parents have produced 100 offspring.

Results of Cross
When F1 generation consists of…	Proportion with round seed phenotype is…	Proportion with wrinkled seed phenotype is…
10 offspring
20 offspring
30 offspring
40 offspring
50 offspring
60 offspring
70 offspring
80 offspring
90 offspring
100 offspring

2. What happened to the proportions of the two phenotypes as the F₁ generation grew from 10 to 100 offspring? Why?

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3. If Mendel had only looked at a single cross that produced ten offspring to determine the pattern of inheritance of seed shape in pea plants, what might he have inferred?

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4. How can two parents with only one “round” allele between them—only 1 out of 4 alleles—produce an F₁ generation in which 50% of individuals have round seeds?

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Next Generation

In the lower middle of the “Experiment Setup” box, click “Next Generation.” Select “Manual Crosses.” You will now be able to choose parents for the next generation (F₂) in the dropdown menus under “Parent 1” and “Parent 2.” You can choose which F₁ offspring to use as parents by rolling over the list of the F₁ offspring in the “Results” box in the middle of the screen. Note which F₁ offspring are wrinkled, then choose two of those names from the menus under “Parent 1” and “Parent 2” to pair them up them for mating.

5. Click the “Cross” button a few times to produce the F₂ generation. What are the results? Do the results support the idea that pea plant seed shape has a dominant/recessive pattern of inheritance? Explain your reasoning.

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Part B: Pod Shape

Click the “Reset” button in the lower right corner of the “Experiment Setup” box. Keeping pea plants as the subject, select “Pod Shape” as the trait you will investigate next. Cross a parent that is homozygous for “Constricted” pod shape with a heterozygote. Once again, repeat the cross until the parent plants have produced 100 offspring.

6. Look at the results of your crosses. Does it appear that pod shape is a dominant/recessive trait? If so, which allele is dominant, and which is recessive?

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7. If you were a pea farmer and you had to produce both the constricted and the inflated varieties of peas to satisfy the market, how would you go about ensuring that your plants would produce adequate amounts of both types? (Hint:Think about what would happen if pea plants were allowed to cross-pollinate.)

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Part C: Flower Position

Reset the experiment setup but keep the pea plant as the model organism. This time, select flower position as the trait to investigate. Once again, you will determine the pattern of inheritance for this trait. This time, however, you will choose which parental genotypes to cross and how to use the results to determine the pattern of inheritance.

8. Use the space below to record the procedure and results of your experiment.

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9. How many offspring did you produce in each cross before you felt confident enough to infer the pattern of inheritance based on your results? Explain your reasoning.

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