Mendel’s Data – Part 1



Mendel’s Data – Part 1

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Introduction

Gregor Mendel studied the inheritance of a number of characteristics in pea plants such as flower color, seed shape, and height. For all of these characteristics he carefully conducted breeding crosses between plants with different forms of the trait. For instance, Mendel crossed purple-flowered plants with white-flowered ones, tall plants with short, and round-seed plants with wrinkled-seed ones. In all cases he started with plants that were pure-bred. His tall plants, for example, came from parents that produced only tall offspring.

Discussion Questions

1. Mendel crossed (bred) tall pea plants with short pea plants. Predict what the offspring were like.

Tall x Short

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Give a reason for your prediction below:

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2. After finding out what Mendel actually got when tall and short plants were crossed, what questions do you have now?

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3. If you were Mendel, what would you have done next?

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4. After finding out what Mendel did next, predict what the offspring of this cross were like:

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5. The table below shows Mendel’s actual F2 results for the tall-short experiments and six others.

Mendel’s F2 Generation Results

|Characteristics |Trait and Number of Plants |Trait and Number of Plants |

|Height |Tall |787 |Short |277 |

|Flower color |Purple |705 |White |224 |

|Flower position |Axial |651 |Terminal |207 |

|Seed color |Yellow |6022 |Green |2001 |

|Seed shape |Round |5474 |Wrinkled |1850 |

|Pod shape |Inflated |882 |Pinched |299 |

|Pod color |Green |428 |Yellow |152 |

Images of Traits

(from )

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Analysis Questions

1. Are the F1 results for height what you expected? Propose a tentative explanation for these results. Consider what could have happened to the factor for shortness in the F1 generation. How did it show up in the F2 generation if it isn’t observed in the F1 plants?

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2. What are the ratios of each trait? (hint: divide tall by short – this gives a ratio of 2.84 to 1)

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Mendel’s Data – Part 2

Predicting and Probability

1. Make a Punnett square for Mendel’s two crosses (parental and F1) for height.

Parental F1

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2. Explain in words how the parental Punnett square predicts what Mendel got for the F1 results.

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3. Explain in words how the F2 Punnett square predicts what Mendel got for the F2 results.

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4. If a coin is tossed, what is the probability that it will land heads up? Is it possible to toss a coin three times and get heads each time? How about if you toss it ten times? One hundred times? Ten thousand times?

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5. Use your understanding of probability from question 4 to answer why the predicted F2 ratio in the Punnett square above does not match the F2 ratio of 2.84 to 1.

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6. Use your understanding of probability from question 4 to answer why seed shape and seed color were closest to the 3:1 ratio in the F2 generation.

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