Students take an inventory of their own easily observable genetic traits. Working in small groups, they observe how their trait inventories differ from those of others. Students record their observations in a data table and make a bar graph to show the most and least common traits in the group.
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1. Begin by demonstrating one of the traits listed on the survey checklist. Ask students who possess this trait to stand. Point out the relative numbers of students standing and sitting for the trait. Continue this process with 2-3 more traits.
2. Explain that traits are observable characteristics we inherit from our parents. Some traits are common in a population (our class) while others are not. And, every person has a different overall combination of traits that makes them unique.
3. Divide students into groups of four or more. Have each student in the group complete a survey (above) to determine their unique combination of the traits described.
4. After students complete the survey, have them tally their group
information on the data table (above) and draw a bar graph on the graph sheet (above).
Optional: You may collect the traits data from the whole class by creating a large wall chart (see example on the right). Have a representative from each group fill in their data. Once all the data has been collected, have the students make a bar graph from the class data or make one large graph together.
Have students practice converting fractions to decimals, then decimals into percentages by calculating the frequency of the following traits in your classroom: tongue rolling, handedness and hand clasping.
Students can then compare their calculated frequencies with those for the general population (provided in the table below).
Example: # of students with the trait/# of students in the class x 100 = ________%
15 tongue rollers / 21 students in the class x 100 = 71%
|Trait||Frequency in General Population*|
|Tongue Rolling||Can roll tongue — 70%
Cannot roll tongue — 30%
|Handedness||Right handed — 93%
Left handed — 7%
|Hand Clasping||Left thumb on top — 55%
Right thumb on top — 44%
No preference — 1%
*Frequencies for traits are from Online Mendelian Inheritance In Man (see http://www.ncbi.nlm.nih.gov/omim/).
1. Ask all students to stand.
2. Have a volunteer call out one of their traits at a time, beginning with #1 on the survey and continuing in sequence. As each trait is called out, direct students who do not share the trait to sit down; students who share the trait remain standing. Once a student sits down, they do not get up again.
3. Have the volunteer call out one of their traits at a time, beginning with question 1 on the Survey and continuing in sequence. For each trait, direct all students who do not share that trait to sit down; students who share the trait remain standing. Once a student sits down, they do not get up again.
4. Continue in this way until the volunteer is the only one standing. Count the number of traits it took to distinguish the volunteer from everyone else in the class. Compare this number with the students' predictions.
5. Repeat with several additional volunteers.
Students may think that the more common traits are "better", but this is not the case. Some traits simply show up more frequently in the human population.
Students familiar with the terms "dominant" and "recessive" may think that dominant traits are more common than recessive traits. However, frequency has very little to do with whether a trait is dominant or recessive. A dominant trait is not necessarily more common and a recessive trait is not necessarily rare in a population. A good example is the trait of polydactyly (having an extra finger or toe). This trait is caused by a single dominant gene, yet is not all that common in the population.