Virtual Genetics Lab: Inheritance in Mendel’s Peas



Virtual Genetics Lab: Inheritance in Mendel’s Peas Worksheet

Learning Goal: To explore patterns of inheritance by simulating Gregor Mendel’s experiments with pea plants.

Prerequisite Knowledge: Before beginning this lab, you should be familiar with these concepts:

• the definitions of allele, dominant, recessive, homozygous, heterozygous, genotype, and phenotype and how these terms apply to genetic traits

• the notation and terminology used to identify parents and first- and second-generation offspring in genetic experiments

• cross-pollination in plants

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

Part A

Seed shape: The F1 generation

Enter the Genetics Lab Room by clicking the button. Then, follow the Lab Procedure.

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|Lab Procedure |

|Choose Pea Plant from the Species Selector. (To review how to select variables for your experiments, watch this video.) |

|In the Experiment Setup box, make sure that Mendelian is checked. Then select Seed Shape as the trait. (You may have to scroll|

|down in the list of traits.) |

|Set the genotypes for Parent 1 and Parent 2. |

|Parent 1: Select Wrinkled for allele 1 and Wrinkled for allele 2. |

|Parent 2: Select Wrinkled for allele 1 and Round for allele 2. |

|In the lower left corner of the Experiment Setup box, make sure the Number of Offspring is set to 10. |

|Click the Cross button. Observe the F1 results. |

|At the top of the Results box in the field with the text Enter graph name here, click and add a title, such as “10 offspring.”|

|Click the Save button in the upper right corner of the Results box to save the data to the Lab Book. |

|Click the Cross button repeatedly until the parents have produced 100 F1 offspring. You can see how many offspring have been |

|produced by watching the F1 Offspring field in the By Generation section of the Results box. |

|Enter a title for the data (such as “100 offspring”). Then click the Save button. |

|Click on the Lab Book on the right side of the lab room to view the data from the crosses. |

|Compare the phenotype summary of the F1 offspring for the 10 crosses to the 100 crosses. |

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

|ANSWER: |

Part B

If Mendel had only looked at a single cross that produced 10 offspring to determine the pattern of inheritance of seed shape in pea plants, what might he have inferred?

|ANSWER: |

Part C

How can two parents with only one round allele between them (1 out of 4 alleles) produce an F1 generation in which 50% of individuals have round seeds? What appears to be the inheritance pattern for seed shape?

|ANSWER: |

Part D

Seed shape: The F2 generation

You probably concluded that the round allele is completely dominant to the wrinkled allele, which explains the results in the F1 generation. Now you will observe what happens in the F2 generation.

|Click the Next Generation button at the bottom of the Experiment Setup box. |

|Select Manual Crosses. |

|Next, you will select parents for the F2 generation from your F1 offspring. You want two wrinkled individuals to be the |

|parents. To determine the phenotypes of individual F1 offspring, roll over the F1 offspring in the Results box in the middle |

|of the lab. For example, when you roll over MF8, the phenotype for that individual is shown in the first box on the left. The |

|other two boxes show the phenotypes of the parents (MF1 and MF2). (MF8 means male-female number 8 -- the eighth offspring, |

|which has both male and female reproductive organs.) |

|Once you have identified two F1 offspring with the wrinkled phenotype, select those individuals using the dropdown menus under|

|Parent 1 and Parent 2 in the Experiment Setup box. |

|Click the Cross button three times until the parents have produced 30 F2 offspring. |

|Observe the proportions of the F2 offspring in the Results box. |

Assuming that the wrinkled allele is recessive to the round allele, which of the following statements best describe the F2 offspring? Select the three that apply.

ANSWER:

____ 100% of the F2 offspring are round.

____ 100% of the F2 offspring are wrinkled.

____ The parents of the F2 generation must be homozygous for the wrinkled allele.

____ All F2 offspring must be heterozygous for the wrinkled allele.

____ All F2 offspring must be homozygous for the wrinkled allele.

| | |

Part E

Pod shape

|In the Experiment Setup box, click the Reset button. |

|Make sure that the Species Selector continues to show Pea Plant as the species. |

|Select Pod Shape as the trait. |

|Set the genotypes for Parent 1 and Parent 2: |

|Parent 1: Select Constricted for allele 1 and Constricted for allele 2. |

|Parent 2: Select Constricted for allele 1 and Inflated for allele 2. |

|Click the Cross button repeatedly until the parents have produced 100 F1 offspring. |

|Observe the results of your crosses. |

Does it appear that pod shape exhibits a dominant and recessive inheritance pattern? If so, which allele is dominant, and which is recessive? How do you know?

|ANSWER: |

Part F

Think it over

Suppose you are a pea farmer and you have to produce both the constricted and the inflated varieties of peas to satisfy the market.

How would you make sure that your plants produce adequate amounts of both types? (Hint: Think about what happens if pea plants are allowed to cross-pollinate.)

|ANSWER: |

Part G

Flower position

In this experiment, you will determine the pattern of inheritance for flower position.

|In the Experiment Setup box, click the Reset button. |

|Make sure that the Species Selector continues to show Pea Plant as the species. |

|Select Flower Position as the trait. |

|Set genotypes for the parents. For example, you could make both parents heterozygous for flower position--one axial allele, |

|one terminal allele. |

|Click the Cross button repeatedly until the parents have produced enough offspring to see a pattern in the inheritance of the |

|traits. |

Which of the following describes the pattern of inheritance supported by your results?

ANSWER:

____ The axial and terminal alleles are codominant.

____ The axial and terminal alleles are incompletely dominant.

____ The terminal allele is completely dominant to the axial allele.

____ The axial allele is completely dominant to the terminal allele.

| | |

Part H

Think it over

For each of the traits you examined (seed shape, pod shape, and flower position), how many offspring did you need to produce in all of the crosses before you felt confident enough to infer the pattern of inheritance based on your results? Explain your reasoning.

|ANSWER: |

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