1

Name:

Fribble Lab

Fribbles are cute, friendly little creatures which love to sit in the palm of your hand or hide in your pocket. They have large eyes and purr softly when they are happy, which is almost always. Having soft purple fur is a dominant trait (A). You have decided to breed fribbles so you can give them to your friends and family as presents. You do have to be careful, however, because there is a nasty recessive gene which causes fribbles to be hairless. (a).

You will be representing the gametes of your fribbles with beads. Each bead should be regarded as a single gamete and the two different colors of the beads represent the 2 alleles of the gene.

A = red bead

a = white bead

1. Start with 60 red beads and 40 white beads in a cup. This represents all of the genes

found in the entire fribble population, also known as its ______.

2. How many diploid individuals are represented in this population?

3. What beads would represent a homozygous dominant individual?

4. Would an individual with one red and one white bead be purple furred or hairless?

5. Write the general Hardy-Weinberg equation.

6. Write the Hardy-Weinberg equation as it applies to this particular population.

7. Complete the chart below predicting what the next generation should be like:

Use the original allele frequencies for the parent population and calculate how many individuals of each genotype will be in the new population and their frequencies using the Hardy-Weinberg equation. The number of individuals for each genotype is calculated by multiplying the expected frequencies by 50 (the total population size).

Parent populations New Populations _

Allele frequency Number of individuals Allele Frequency

of each genotype

(and frequency)

A / a / AA
( ) / Aa
( ) / aa
( ) / A / a

8. State the 5 conditions that are necessary for the Hardy-Weinberg equation to hold true:

a.

b.

c.

d.

e.

Without looking, remove 2 beads from the cup. In the chart below, make a tally to keep track of the number of individuals of each genotype (AA, Aa, or aa) Return the 2 beads to the cup. Shake the cup to mix the beads and take out another pair. Record them in the chart. Repeat this process until you have picked out 50 pairs and recorded them.

AA / Aa / aa

Totals: ______

9. Calculate the frequency of each genotype. (Number with that genotype divided by the total number of individuals of all genotypes) Show your work.

AA: Aa: aa:

10. What is the number of each type of bead color (allele) in your gene pool at the end of this generation?

A = a =

11. How do these numbers compare to those at the start of the experiment?

12. If you repeated this process for 25 generations, what would happen to the number of each type of allele over that time?

13. How do your expected results compare with your actual results?

14. What would cause your actual results to differ from the expected results?

15. Is this population evolving? Explain.

Part 2

As you prepare to give your new baby fribbles to your friends and family, you realize that what makes fribbles so attractive is their soft purple fur. You decide that in future generations, you will not use hairless fribbles as your parents, but will only allow fribbles with hair to mate.

In this section, do not return the beads to the cup after each pair is drawn. Instead, put them into the cups labeled AA, Aa and aa. Keep drawing out pairs of beads and putting them into the appropriate cups until you run out of beads. Record your tallies in the chart below for the first generation.

Genotype tally Genotype frequency Gene Phenotype

Frequency Frequency

Generation / AA / Aa / aa / AA / Aa / aa / A / a / Hair / Hairless
1
2
3
4
5

Repeat this process for 5 generations, but when you start a new generation, do not put the beads from the aa cup back into the gene pool cup. Only start with the beads from the AA and Aa cups.

1. What happens to the frequencies of the two alleles as this process continues?

2. If this type of selection would all of the recessive alleles eventually be eliminated from the population? Why or why not?

3. Why aren’t recessive alleles such as blue eyes eliminated from our population?

4. Why aren’t recessive alleles such as diabetes eliminated from our population?

5. Why aren’t deadly recessive alleles such as Tay Sachs eliminated from our population?

Part 3

Now an amazing thing happens! Santa decided that he wants to give fribbles to all the good little girls and boys this year. Since he is paying $100 per fribble, you decide that selling almost all of your fribbles to Santa is a great way to fund your college education! (Yea! No more scholarship applications to complete!!! J ) When his elves come to get the fribbles while you were gone to school, you discover that there are only 10 fribbles left and 7 of them have no fur!

1. What is the general term used to describe when a chance event like this changes the allele frequencies of a population?

2. What you have left in your room for fribbles is similar to the group left after a disaster such as an earthquake or a fire in the wild. What is the name for this situation in which the surviving gene pool is not the same as the original gene pool?

3. How will the allele frequencies in your current population compare over time with those of your original population?

Why?

4. Santa decides that he is going to start his own fribble farm since you charged him such ridiculously high prices this year to buy yours. He saves 10 fribbles, all with fur. (Smart Santa!) Again, his starter population now has a different allele frequency than the original population. What is this called?

5. While you are gone to school, your 10 fribbles are lonely at home. They start to call out with ultrasonic voices (which only fribbles can hear). One day when you get home, you discover that 50 new fribbles have come from the wild and are now want to stay with you too. What is this called?

6. If the new fribbles from the wild have different allele frequencies from your 10, what will happen to the allele frequencies in your population over time compared to your original population?

7. If the genes for fribble fur color were to mutate, how would you show that with your beads in this representation?