How to Proceed

Read through the introductory materials below.
Open the Unit 7 Experiment Answer Sheet and complete the following Experiment exercises this unit:

Experiment 7 Exercise 1 – Evolutionary Change without Natural Selection (~1 hr)
Experiment 7 Exercise 2 – Evolutionary Change with Natural Selection (~1 hr)
Experiment 7 Exercise 3 – Mechanisms of Evolutionary Change (~30 min)

Materials Needed

For the first two exercises you will need the following:

· 50 red M&Ms and 50 green M&Ms or 50 each of two items that are distinguishable by color but are similar in size and texture (e.g., dimes and pennies, two different color beads).

· Four containers large enough to hold the above items.

Experiment 7 Exercise 1: Evolutionary Change without Natural Selection

In this first exercise, we are going to look for evidence of evolutionary change in a population in the absence of natural selection by looking at the change in allele frequencies over time in a simulated population. We will start with a population of 50 individuals in which there are two alternate alleles ( H and h ) in equal proportions (each at a frequency of 0.5 or 50%). Individuals have the possible genotypes: HH , Hh or hh . These two alleles do not offer any selective advantage, so neither is selected for or against, meaning they are neutral. We will record the frequency of these alleles over 10 generations. Prior to advancing on to the next generation, six alleles (= three individuals) will be removed at random.

Before you begin, answer the following:

Question

1. What is your prediction as to what will happen to the frequencies (note that this is different than the number) of these two alleles over 10 generations? Word your prediction as an “if-then” statement based on the experiment design. (1 pts).

Procedure:

A. Let 50 M&M’s of one color (i.e. red) represent the dominant allele (H) and 50 M&M’s of another color (i.e. green) represent the recessive allele (h).

B. Let one container represent the Habitat where random mating occurs. Place all of the M&Ms (or other items) into this container. This is your starting gene pool of your “parent” population or Generation 0.

C. Label the other three containers HH for homozygous dominant individuals, Hh for heterozygous individuals and hh for the homozygous recessive individuals. Notice that individuals have two alleles.

D. Mix up your Habitat well and without looking, select two items (alleles) at a time; these two alleles represent a single individual. On a piece of paper, keep track of the genotypes of the individuals withdrawn. For instance, if you draw one red and one green M&M, that counts towards “Number of Hh individuals.” If you draw two red M&Ms, that counts towards “Number of HH individuals” and so on.

E. Continue drawing pairs and recording the results until all items (alleles) have been withdrawn and sorted. Be sure to place the “offspring” into the appropriate dish: HH, Hh, or hh. Note that the total number of individuals will be half the total number of items because each individual requires two alleles, so you will have 50 offspring (but 100 alleles). Record the number of HH, Hh and hh individuals drawn for Generation 1 in Table 1 below.

F. Next count (or calculate) the total number of H and the total number of h alleles for the first generation and record the number in Table 1 below in the columns labeled “Number of H Alleles” and “Number of h Alleles.”

G. Add up the total number of H alleles and h alleles for the first generation and record this number in the column labeled “Total Number of Alleles.” If you did everything correct, you should still have 50 H alleles and 50 h alleles. This has already been entered for you in the Table below for Generation 1.

H. Combine the HH, Hh and hh individuals back into the Habitat container and mix well. Randomly remove three pairs of alleles (= three individuals, six items) and set them aside.

I. Repeat steps D through H to obtain Generations 2 through 10. Remember to randomly remove three pairs of alleles each time. Because I know that each generation will have six fewer alleles, I have also entered the total number of alleles in the Table below. Be sure that is the number your alleles add up to!

Here is a photograph of this process after six generations. The sixth generation has been distributed into the HH, Hh and hh containers. Note that dimes and pennies have been used.

image1.png

J. After entering your number of individuals and allele counts for each generation, you now need to determine the allele frequency of H and h for each generation and record them the Table below. To determine allele frequency take:

· # of H /Total alleles in the generation = Allele frequency of H (express as a decimal)

· # of h /Total alleles in the generation = Allele frequency of h

Note that the total number of alleles will change each generation, but the frequency the H allele plus the frequency of the h allele should add up to 1.0 for each generation.

Save your completed Unit 7 Experiment Answer Sheet and submit itno later than Sunday midnight (CT).

Evolutionary Change and Natural Selection – Introduction
Evolution is descent with modification and includes small-scale evolutionary change (microevolution) as measured by changes in gene frequency in a population from one generation to the next and large-scale evolutionary (macroevolution) change as evidenced by speciation events. Several mechanisms contribute to evolutionary change, such as natural selection, a process in which individuals with certain beneficial traits are more likely to survive and reproduce. Natural selection is also responsible for the loss of lethal or detrimental traits from a population. It is important to keep in mind that evolution does not act on individuals; it acts on populations. Natural selection, however, does act on individuals within a population and can result in evolutionary change of that population over time.
Populations do not always change due to Natural Selection, since there are several conditions that must be met in order for Natural selection to occur:

Individuals within a population must vary; they do all exhibit identical traits.
Some traits are “better” than others or “worse” than others.
The traits that vary are heritable and not simply acquired.
The “better” individuals have more success reproducing and produce more offspring.

IF these conditions are met, then in successive generations, more offspring will exhibit the beneficial trait (or conversely, a detrimental trait will be lost).
Recall that DNA contains sequences that code for particular proteins or traits, these sequences are called genes. The alternate forms of genes are called alleles and these alleles exist in pairs because chromosomes exist in pairs. A dominant allele is one that masks another (recessive) allele; dominant does NOT mean a given allele is more frequent or necessarily better. A recessive allele is one that requires two copies to be expressed. Evolutionary biologists are interested in the frequency of alleles within a population and how they change over time (= microevolution).
Be sure that you read through our Unit 7 online lecture this unit on Evolution as well as your text book readings. Open the Unit 7 Experiment Answer Sheet and work through the first two exercises.
Mechanisms of Evolutionary Change – Introduction
There are other mechanisms besides Natural Selection that can lead to evolutionary change. These include:

Genetic drift (random changes in the gene pool)
Mutations
Gene flow (e.g., immigration and emigration)
Nonrandom mating (e.g., inbreeding, sexual selection, assortative mating)

Be sure to review our online lecture on Evolution and pp 260-264 in your book before starting this exercise. You will be using the following website for this exercise. Be sure you are able to open it and use it:
BioMan Biology. No date. Biology Games and Virtual Labs: Evolution
http://biomanbio.com/GamesandLabs/EvoClassGames/aaevo.html (Links to an external site.)
When you are ready, open your Unit 7 Experiment Answer Sheet and complete Exercise 3: Mechanisms of Evolutionary Change.