Return to Biology IndexPopulation Study and Applications Using PTC Paper

Susan H. Smigla Leslie Lewis Elementary

1431 N. Leamington Ave.

Chicago, Illinois 60651

(312) 534-3060Objectives:

1) To understand the terms dominant, recessive, haploid (monoploid), diploid,

genotype, phenotype, scientific sampling and scientific modeling.

2) To know and understand how human population traits such as PTC tasting,

widow's peak, bent little finger, tongue rolling and many other traits are

distributed.

3) To understand how the various genotypic ratios are distributed throughout

a population.

4) To understand the laws of chance and how they are applied to population

genetics.Materials:

PTC Testing Paper (if testing for that trait), graph paper, 2 coins of the same

denomination for each team. (Students can provide their own coins.)Strategy:

To demonstrate scientific sampling, have the class test themselves to see which

students in the class are PTC tasters and which are not. Have the students

test their families and/or use the data from several classes to provide a

sufficiently large representation of the population to work with.Graph the data. Title the graph PTC Tasters (or PTC Nontasters). Label the

horizontal axis "Number of Tasters" (Nontasters) and the vertical axis "Total

Number of People Sampled". Plot a "best fit curve". To obtain a ratio, divide

the total number of tasters (nontasters) by the total number of people sampled.

To demonstrate scientific modeling, divide the class into partners. Use a "coin

toss" with 2 coins of the same type for each pair of partners. Put the coins in

the hand, cup the hands and shake them. Open up the hands and allow the coins

to roll out onto the table. Put down tally marks in the appropriate columns to

reflect the combinations shown.Counts | Possible Combinations|2 Heads |2 Tails |1Head/1TailTotal | | | |Ratio | | | |Total Number of Flips |Total the columns.Obtain the ratio by dividing the total of a combination (ex.

2 Heads) by the total number of flips.

In this genetic experiment, "T" is the symbol for tasters and "t" is the symbol

for nontasters. "Tt" therefore would be the symbol for a heterozygous taster.

Pretend that 2 heads is the "genotype" TT, 2 tails is the "genotype" tt and 1

head/1 tail is the "genotype" Tt. Make a graph of the "tasters" as shown in the

data table for your coin flips. Title this graph "Penny Tasters". Mark the

horizontal axis "Number of Tasters" and the vertical axis "Number of Flips".

Plot a "best fit curve". Compare the curves of the graph that you made of the

actual PTC paper tasters with the curve of the graph that you made of the

"tasters" that you obtained from your "coin toss".

On a punnett square, show the possible results that would occur for the

following matches and record the ratio of tasters to nontasters. A) TTxTT,

B) TTxTt, C) TtxTt, D) ttxtt, E) TTxtt and F) Ttxtt.Study Questions:

1) Based on the data table from your "coin toss", how many people in your

"population" would be "tasters"? How many would be "nontasters"?

2) Based on the data table from your "coin toss", determine the ratios of the

coin "tasters" to "nontasters". How does this correlate with the data that you

have obtained from actual population samples?

3) How does the "coin toss" demonstrate random pairings of genes? (Explain)

4) Gamblers place bets on things that have the greatest odds of occurring. If

you were to place a bet on the coin toss, which combination would you bet upon?

Why?

5) In looking at the data of the tasters vs nontasters, which genotype comes up

most frequently? Which phenotype comes up most frequently?

6) Do you think that scientists are able to come up with reasonable statistics

based on scientific sampling and modeling? Defend your answer.

7) Based on your data, can you tell which trait is the dominant trait and which

trait is recessive? How?

8) Looking at the data obtained on your graphs, do the curves go up in a

predictable pattern?

9) Based on your graphs, if you were to sample 200 people, what do you think

the total number of tasters would be? Nontasters? How about if you sampled 500

people? What would be your results if you sampled 1000? How are you able to

predict your answers?

10) Based on the data obtained from your punnett square matches, if you were to

pretend that the ability to taste was a desirable trait to mate for, which mates

would insure the most tasters in the offspring? Which matches would produce the

least number of offspring that are tasters?

11) Can two parents that are tasters have children that are nontasters?

Explain.

12) The appearance of various genetic deformities and diseases in a population

can be studied by the same techniques that we have been using. Do you believe

that couples about to get married should have genetic counseling?

13) What if you have found out that you were a carrier for a genetic defect,

what action do you think that you should take? What about if it was your

spouse?Extension:

1) Using a pedigree chart test your family for one or several of these traits:

1) PTC Tasting 2) Tongue Rolling

3) Widow's Peak 4) Hair on the 2nd finger joint

5) Attached ear lobe 6) Bent little finger

The more people in your family that you can test, (Grandparents, Aunts, Uncles,

Cousins, etc.) the better your data will be. Be sure that you differentiate

between blood relatives and relatives through marriage.

2) Set up a data table and include ratios for your results.

3) Set up a graph and interpret your results. Be sure to include a "best fit

curve".

4) Based on your pedigree, try to figure out the genotype for the traits that

you have sampled.

5) Based on your graph and ratios, calculate the percentage of the population

that carries these features and whether the trait is dominant or recessive.

Determine whether you have a large enough population sampled to do these

calculations and how the size of the sampled population would affect your

ability to have a valid conclusion for your data.