Thumb Measurement and Thumb Variation Lab (Genetics)
(Download the MS Word version of this document.)
Purpose
- To measure the phenotypic variation of thumbs in students in the classroom.
- To calculate the average measured thumb length in a population.
- To calculate the standard deviation of the measured thumb lengths in a population.
- To analyze reasons why there is variation in a human population.
Introduction
The Thumb Variation Lab explores not only measuring in the metric system but also serves as an introduction to statistical analysis of data taken by a simple measurement from the human hand, as well as thumb genetics. The "thumb bending gene" is determined by a pair of gene. The two thumb alleles include: a more common dominant gene for "straight" thumbs and a recessive gene for "hitch hiker thumb" (or bent). Those people with two recessive genes for hitchhiker's thumb are able to bend the distal joint of that digit, bending their thumbs at an angle of 45 degrees or more. This is also called hyperextension of the thumb. People who carry either one allele or two alleles for a thumb that is straight, or close to being straight, express the dominant allele.
You will be identifying your own thumb, and then everyone elses, as to which phenotype it is, in your class. Once you have determined the types of thumbs that everyone has, you will be measuring, in millimeters, and recording the length of each person's thumb. The data will then be analyzed using a spreadsheet program called Excel.
Materials
- thumb
- metric ruler, mm and cm
- paper
- computer with MS Excel
Procedure
1. Determine whether or not you have a hitchhiker's thumb by comparing to the diagram below.
2. By using the picture below, measure your thumb in millimeters from joint 2 to the tip of your finger. Do not include the measurement of your fingernail.
(You should use this picture to determine what to measure)
3. Hand-draw a data table like the one below on your paper with 3 columns: NHHT length (mm) (non hitch hiker thumb length in millimeters), HHT length (mm) (hitch hiker thumb length in millimeters), and initials (the person's initials, first and last, that you measured) or you can write out that person's name instead.
| NHHT length (mm) | HHT length (mm) | initials |
|---|---|---|
4. Record the measurement of your own thumb in millimeters in "NHHT length (mm)" (see below) if you have a straight thumb and in column "HHT length (mm)" if you have a hitchhiker's thumb. Put your initials next to your thumb measurement.
5. Record the measurements of your classmates' thumbs (determining if they have hitchhiker thumbs or not) on the remaining part of the data table. Count the number of students in the room to make sure you have a measurement for each person. Make your best guess as to whether or not that person has HHT or NHHT.
6. Repeat steps #5 and #6 for another class (or a group of teachers) at school. Your teacher will tell you which class to measure.
Analysis of Data/Conclusion
1. Working with a partner, log into CASTOR and then start the program, MS Excel (Start>Programs>Microsoft Excel), to create a spreadsheet of your data from the two classes.
2. Save the spreadsheet into your shared folder on the H: drive. Name it something that you can remember.
3. Using the data you hand-collected, enter the values for each student in the two classes into Excel. Keep the data from the two classes separate.
4. Use the spreadsheet to calculate the following: (Your teacher will give you a demo on how to start this.)
a. The mean (average) thumb lengths in your class for HHT and for NHHT, that is: =AVERAGE(A2..Z2). Label the cell where you did the average for your class.
b. The mean (average) thumb lengths in another class for HHT and for NHHT, that is: =AVERAGE(A2..Z2). Label the cell where you did the average for the other class.
c. The standard deviation (Standard deviation is a way to measure how much variation you have in a population compared to the population's mean.) calculation for each class (a and b above), that is: =STDEV(A2..Z2). Label the cell where you did the standard deviations.
d. Extra credit if you can figure out how to make an average calculation and a standard deviation calculation for BOTH classes on your spreadsheet.
Your spreadsheet will look something like this when it is finished with each cell done correctly and labeled. (This would represent data from one class.)
The formula for standard deviation for HHT you would enter into cell E2 would be: =STDEV(B10..B14)
The formula for standard deviation for NHHT you would enter into cell E4 would be: =STDEV(A2..A6)
The formula for the mean (or average) length for NHHT you would enter into cell E6 would be: =AVERAGE(A2..A6)
The formula for the mean (or average) length for HHT you would enter into cell E8 would be: =AVERAGE(B10..B14)
5. Write at least a one page paper (covering all lines on one page) explaining why there is variation (or measureable differences) in our experiment/measurements or why there is not. What sort of results did you get? Were there any patterns that you could detect? Include ideas of: Why are students in junior high so different? Why are students at KJHS so different? Possibilities of error? If you measured the teachers' thumbs, were they different? What would explain variation in different aged populations?
What to Turn in (each person)
- 2 hand-drawn data tables (One per each class with individual student's measurements) (30 pts, 15 pts each)
- 1 spreadsheet printed off (print it twice, one for each student or have teacher check that he saw it) (30 pts)
- 1 write-up on a piece of notebook paper discussing why we have so much (or so little) variation in our experiment (40 pts)
- Staple each of these papers together in the order above. Make sure that your name and period are written on the top page.
