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Activities: the evolutionary causes of biodiversity

Hint: the background information that will help you complete this activity is found in the videos and articles.
Activity 1. Reproductive potential and natural selection
This activity uses bell peppers to provide an example of the reproductive potential of a species. You can do the activity by yourself or with friends.
Background: Fitness is defined by the reproductive success of an organism. An individual with higher fitness produces more viable offspring (therefore passing on a higher proportion of genes to the next generation) than an individual with lower fitness. The traits of individuals with higher fitness become more and more common as generations go by, while the traits of individuals with lower fitness may eventually be lost from the population. This is the process that Darwin called "natural selection".
In order for natural selection to occur, there must be variation among individuals and a “struggle for existence” in which not all individuals survive. There are simply not enough resources for all individuals to survive, so variation among individuals determines fitness and how well an individual does in a given environment. Without taking into account genetic mutations, if there were enough resources for all members of a population to survive and reproduce, the population would look pretty much the same from one generation to the next. But in reality, most types of organisms produce many more offspring than can possibly survive.
Materials:
  • 1 green bell pepper
  • scissors or knife to cut open the pepper
  • plates or napkins
Procedure:
a)    Look at your pepper before you cut it open. This is generation 1. Write down your prediction for how many plants it would produce if each of its seeds survived. This is generation 2. Then write down your prediction for how many plants would be produced in the third and fourth generations if each generation has the same number of seeds as the generation 1 pepper, each seed successfully becomes a plant, and each plant produces only 1 pepper.
b)   Cut the pepper open carefully and count all the seeds inside. Next, answer these questions:
1.     How many seeds were in this generation 1 pepper?
2.     If all of these seeds sprout and successfully become new plants (generation 2) how many plants will be in generation 2?
3.     Each generation 2 plant produces one pepper and each pepper has the same number of seeds as your answer to question 1. How many total seeds are produced in generation 2?
4.     Each of those generation 2 seeds successfully grows into a plant (generation 3). How many plants are in generation 3?
5.     Each of those generation 3 plants produces one pepper, which has the same number of seeds as the original generation 1 pepper. How many total seeds are produced by generation 3?
6.     Do the same calculations for generation 4. How many total seeds are produced by generation 4 plants?
7.     Can you make a graph showing the number of seeds produced in each generation?
c)    Answer the following questions:
i.         Compare your predictions with your results. Were your predictions close to your results? Did your predictions underestimate or overestimate the number of plants produced?
ii.         If a single pepper is capable of producing so many offspring and such a large population, why do we not see huge populations of peppers covering the planet?
iii.         What factors might change the results? (Hint: is it realistic that all peppers will have the same number of seeds or that each plant will produce only one pepper?)
Activity 2. Individual variation in human traits
Background: Variation exists among the individuals of a single species. We only have to look at each other to see evidence of the variation in body size, shape and height, or in the color of hair, eyes, and skin.
Some traits are controlled by many genes that act together. For example, human skin color is determined by multiple genes. But some traits, called single gene traits, are controlled by one gene with only two possible alleles. This results in two distinctly different physical appearances or phenotypes.
The ability to roll your tongue, for example, is determined by a single gene. A person can either roll their tongue or they can’t; there is no in-between.
In this activity, you will summarize your phenotype, the visible expression, for seven different single gene traits by using a genetic wheel (provided). This activity is a lot more fun when you compare your results with your friends and family!
The traits:
Laugh dimples: when you laugh or smile broadly, do you have dimples in your cheeks?  No = ll on the genetic wheel; yes = L on the genetic wheel
Tongue roll: can you roll your tongue into a “U” shape? No = tt on the genetic wheel; yes = T.
Crossing thumbs: when you clasp your hands together with your fingers intertwined, is your right thumb on top of your left or vice versa? Right on top = cc on the genetic wheel; left on top = C.
Pinkies: when you put your hands side by side, with the palms facing you, are your little fingers straight or do their ends bend noticeably toward the ring fingers? Straight = pp on the genetic wheel; bent = P
Ear lobes: are your earlobes attached directly to the side of your face, or do they hang down freely a bit? Attached = ee on the genetic wheel; free = E.
Widow’s peak: does the hair at the top of your forehead form a straight line, or does it come down in a distinct V-shape in the center? Straight = ww on the genetic wheel; V-shaped = W. (Note: male pattern baldness is not the same as a widow’s peak)
Bending thumbs (hitchhiker’s thumb): when you give the thumbs up sign (hold your arm out with your hand forming a fist and your thumb sticking up), is the tip of your thumb bent back at an angle of 50 degrees or more? Bent 50 degrees or more = bb on the genetic wheel; straighter thumb = B.
Activity procedure:
1.     Review the list of single gene traits and determine which phenotype you have for each trait.
2.     Plot your variation on the genetic wheel provided. Begin in the center of the wheel with the “L” or “ll” expressions for dimples.  If you have dimples, color the “L” section and plot the rest of your traits on the top half of the wheel.  If you do not have dimples, color the “ll” section and plot the rest of your traits on the bottom half of the wheel. Each section that you color should be touching the previous trait section so that they are all connected.
3.     Work your way through the list of traits and continue plotting your traits on the wheel until you have reached a number on the outside edge of the wheel. NOTE: this number doesn’t have any significance. It’s just a placeholder to help you compare you genetic variation with a friend.
Once you’re done, think about these questions or discuss them with a friend:
4.     Compare your genetic wheel results with somebody else’s. Do they show the same pattern of colored sections and final placeholder number?
5.     If you had more people do this activity, do you think there would be new color patterns and final placeholder numbers?

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