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Science Period __________________ Name _____________________

Human Traits Lab Date _____________________

Introduction:

You are a large collection of physical traits or phenotypes. A phenotype is the physical appearance of a trait that is determined by a pair of alleles. The pair of alleles (the letters) is the genotype for that trait. If you knew many phenotypic traits of another person, you would be able to identify them because the chances of one person sharing all of the same phenotypes is very small.

Scientific Question:

Are phenotypes controlled by dominant alleles more common than phenotypes controlled by recessive alleles?

Materials:

A partner, a “leaf”, a textbook

Hypothesis: Write a hypothesis reflecting your ideas about the scientific question. (Use a complete sentence.)

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Procedure: What are your phenotypes?

1. With a partner, determine your phenotype for each trait. Circle it in the data table. Look at the figures on the next page and on pages 116-117 in your textbook for descriptions of each phenotype. Do your best.

2. Circle your phenotypes on the leaf and attach your leaf to the correct branch of our genetics tree.

3. Add your phenotypes to the table up front.

4. When everyone has recorded their phenotypes in the table, count the number of students who have each phenotype. Record that number in your data table. Also record the total number of students.

Data Table Total Number of Students = __________

| | | | |

|Dominant phenotypes |Number |Recessive phenotypes |Number |

|a. Free earlobes | |Attached earlobes | |

|b. Hitchiker’s thumb | |Straight thumb | |

|c. Tongue roller | |Cannot roll tongue | |

|d. Widow’s peak | |Straight hairline | |

|e. Cleft chin | |Smooth chin | |

|f. Smile dimples | |No smile dimples | |

|a. Earlobes |[pic] |

|Free earlobes dangle and are not directly attached to the face. |Free Attached |

|Attached earlobes are connected to the side of the face and are | |

|recessive. | |

| | |

|b. Thumb |[pic] Hitchhiker’s thumb |

|A thumb tip that bends backward more than 30 degrees is called | |

|the hitchhiker’s thumb and is dominant to a straight thumb. | |

|c. Tongue rolling |[pic] Tongue rolling |

|The ability to roll the tongue is dominant to the lack of this | |

|ability. | |

|d. Hairline | |

|The widow’s peak hairline comes to a point in the center of the |[pic] |

|forehead. | |

Data Analysis:

1. List the dominant phenotypes that were shown by the majority of the class? __________________

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2. List the recessive phenotypes that were shown by the majority of the class? __________________

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3. Look at the genetic traits tree. How many leaves are on your branch? ______________________

Did you expect another student to share three of the same phenotypes as you? Why or why not? __________________________________________________________________________________

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4. What is the most common combination of phenotypes on the genetic traits tree? _______________

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5. Are there any branches with only 1 leaf on them? If so, how many? ________________________

Conclusion:

Do your data support your hypothesis that you proposed at the beginning? Write an answer citing specific examples from the data. (Use complete sentences.)

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