BIO 1100 Unit II Assignment—Genetics Worksheet

Gregor Mendel’s Experiments, Theories, and Findings

Mendel observed that pea plants had traits, such as color, that were either “one or the other,” never something in between. Discuss the correlation between Mendel’s factors, what they might be, and why pea plant traits come in one form or another—e.g., gray or dark red—rather than blended.

Your response must be at least 75 words in length. (Type your response in the blank area below; it will expand as needed.)

Over a 10 year period, Mendel studied almost 30,000 pea plants. His experiments consisted of controlled mattings between plants with different traits that included seed shape (round or wrinkled), seed color (yellow or green), flower color (purple or white), and stem length (tall or dwarf). Mendel carefully took pollen (which produces sperm) from the anthers of one pea plant and applied it to the carpel (the egg-container structure) of another pea plant. Growing seed that resulted from these controlled mattings enabled Mendel to evaluate the role of each parent in producing the traits of the offspring. His experiments demonstrated that both parents contribute equal amounts of genic information to their offspring. The pattern of inheritance Mendel described occurs primarily in traits that are the result of a single gene with few distinct alleles. Recessive alleles can only be seen if a dominate allele is not also present. So wrinkled seeds with recessive alleles produce a pea of one color and round seeds with dominate alleles will produce another pea color.

Let’s imagine that we are studying only one trait, that of green- or yellow-colored seeds. Mendel bred his peas until they either produced seeds of one color or the other. These purebred plants he called the p generation (“p” for parental generation). He then cross bred green plants with yellow ones and discovered that all the offspring were yellow-colored. Mendel called the offspring of the purebred plants the F1 generation.

Explain why all the offspring in the F1 generation were yellow instead of half being yellow and half green, or some other mix of the colors. Hint: Remember that Mendel coined the terms dominant and recessive.

Your response must be at least 75 words in length. (Type your response in the blank area below; it will expand as needed.)

The offspring in the F1 generation were yellow because the seeds carried two different alleles called heterozygous genotype. Some alleles are recessive and some are dominant. Recessive alleles can only be seen if a copy of a dominant allele is not also present. Often a recessive allele is one that codes for a nonfunctional protein and heterozygotes (dominate) carrying one copy of the functional allele have normal phenotypes (the allele that give the physical traits). Dominate alleles are seen even when a recessive allele is present. Since the yellow color is dominate and the green is recessive, when both yellow and green are present, the yellow will show.

Punnett Squares

Reginald Punnett was a British geneticist who developed the Punnett square to explain how the chromosomes of parents cross and produce offspring. In order to solve genetics problems using a Punnett square, it is necessary to a) understand the associated vocabulary and b) understand some of the rules for solving the problems.

Before you continue with the problems below, review the meaning of the terms allele, dominant, recessive, homozygous, heterozygous, genotype and phenotype.

You should also review the Punnett Square Basics video linked in the unit lesson.

In this first problem (question #3), the key and genotype of the parents will be done for you as an example. For problems #4 and #5, you will fill in those details based on the information in the question.

Remember, when asked for the genotypic ratio, it may be expressed as 25%(GG):50%(Gg):25%(gg), for example. Or, you may write it more succinctly as 1GG:2Gg:1gg. Either way will be correct.

The phenotypic ratio will use descriptive terms, for example, 3(Green):1(clear), 2(Green):2(clear), or whatever it may be depending on the results of your cross.

In corn plants, the allele for green kernels (G) is dominant over clear kernels (g). Cross a homozygous dominant plant with a homozygous recessive plant.

Fill in the Punnett square below and give the ratios for each question beneath the Punnett Square.

Key: G = green kernels, g = clear kernels

What is the genotypic ratio of the offspring in Question 3? 100% (Gg)

What is the phenotypic ratio of the offspring in Question 3? 100% (Gg)

Yellow seeds are dominant over green seeds in pea plants. Cross a heterozygous (yellow seeded) plant with a green seeded plant.

Key: Y= Yellow Seeds, y= Green Seeds

What is the genotypic ratio of the offspring in Question 4? 50% (Yy) : 50% (yy)

What is the phenotypic ratio of the offspring in Question? 50% (Yy) Yellow : 50% (yy) Green

Now cross two of the heterozygous F1 offspring from question #2.

What is the genotypic ratio of the offspring in Question 5? 25% (YY) : 50% (Yy): 25% (yy)

What is the phenotypic ratio of the offspring in Question 5? 75% (Yellow) :25%(Green)

Consider the resulting ratio of crossing the two heterozygous pea plants in question #5. We will use this ratio in a short activity exploring probability. Keep in mind that crossing two individuals that are heterozygous for a certain trait is similar to flipping two coins. Each coin has two sides (we might think of each side as an “allele”) and the chances of flipping heads/heads, heads/tails or tails/tails should be similar to the ratio we see when crossing two heterozygotes.

For this simple activity, you will need two coins (pennies, nickels, dimes, quarters, or a mix of any of those). Alternatively, you may google a coin-flipper simulator that will allow you to flip two coins at once. You will also need a piece of scratch paper and a pen or pencil.

Directions: Flip the two coins simultaneously at least 50 times. For each flip of the pair of coins, you will record the results on a piece of scratch paper. You might set up a table like the one below to record your results. Once you have flipped the coins at least 50 times, enter the number of heads/heads, heads/tails and tails/tails in Table 1 below.

Now determine the ratio for your results. You will do this by dividing the number for each result by the total number of flips, and then multiply by 100.

(Example: If the number of heads/heads is 9 then 9/50 = .18, .18x100 = 18%), Repeat this mathematical procedure for heads/tails and tails/tails)

Table 1

Compare the resulting ratio from the question #5 cross of two heterozygous parents to the ratio from the coin flipping exercise. Are there similarities? If so, what are they?

Yes. In both cases the ratio was similar (not exact) to the genotypic ration

What might be done to make the ratio from the coin flipping exercise become more similar to the ratio from question #5? (Hint: Consider that more data equals better accuracy.)

The only way to achieve more similar results is to continue flipping the coin (add more flips). The more flips of a coin, the more data will be obtained. The more data that is obtained, the results will be more accurate.

Cancer Risk Factors

7. This question deals with cancer and risk factors. Begin by going to the website http://www.cancer.org/

Click “Cancer A-Z” in the upper left corner. The page that comes up will provide links to information on breast cancer, colon and rectal cancer, lung cancer, prostate cancer, and skin cancer. Review the information for each these cancers.

Next, write an essay that briefly discusses your own risk factors for each type of cancer and steps you might take to decrease those risk factors. Be sure to address all five types of cancer.

You do not have to disclose any actual personal information if you do not wish to do so. You may create a fictional character and discuss his or her risk factors instead. Be sure to address all five types of cancer.

Your response must be at least 300 words in length. (Type your response below)

Cancer is a disease that, sadly, will affect most people at some point in their lives, either by a direct diagnosis or a diagnosis of a loved one. Some cancers develop during an individual’s lifetime and other types of cancers are inherited genetically. There are five main types of cancer: breast cancer, colon cancer, lung cancer, prostate cancer and skin cancer. I am a female, 42 years old, and I want to discuss my risk factors for each cancer.

Breast Cancer

Certain breast cancer risk factors are related to personal behaviors, such as diet and exercise and others are hereditary. Risk factors that increase the risk of breast cancer that you can do nothing about include: being a woman, getting older, inherited genes, having dense breast tissue, and even going through menopause after age 55. Lifestyle- related risk factors that could increase the chance of breast cancer include: Drinking alcohol, being overweight or obese, not being physically active, not having any children or having your first child after 30, not breast feeding, some birth control methods, and even having breast implants. Keeping these risk factors in mind, I want to evaluate my risks for getting breast cancer. I am female but do not have a history of breast cancer in my family. Since I am 42, my risk is increasing (getting older.) All medical test have come back good, so the future appears bright. My alcohol intake is limited to a margarita every two to three weeks and I do not smoke, so not an elevated risk there. I am not overweight and I am physically active. I have 2 children (before the age of 30) but did not breast feed either. I did take birth control for many years before having my children, which will elevate my risk slightly but I no longer take any time of hormone treatments. I believe I am already doing what I can to lower my risks for breast cancer and have exams regularly, so I will continue doing what I’m doing.

Colon Cancer

Certain colon cancer risk factors are related to personal behaviors, such as diet and exercise and others are hereditary. Risk factors that increase the risk of colon cancer that you can do nothing about include: being older (over 50), a family history or personal history of colorectal polyps / cancer / inflammatory bowel disease (IBD), and having type 2 diabetes. Lifestyle- related risk factors that could increase the chance of colon cancer include: being overweight or obese, physical inactivity, a diet that is high in red meats and processed meats, smoking, and heavy alcohol use. Keeping all of these risk factors in mind, the only cause for concern I have is my family history with this issue. My mother and sister have had several polyps removed, so I am at a higher risk for this type of cancer. After being tested, none have been cancerous. The main thing I need to do to be preventative is schedule a screening to see if I have polyps as well.

Lung Cancer

Certain lung cancer risk factors are related to personal behaviors, such as diet and exercise and others are hereditary. Risk factors that increase the risk of lung cancer that you can do nothing about include: having personal or family history of lung cancer. Lifestyle- related risk factors that could increase the chance of lung cancer include: tobacco smoke, exposure to radon, exposure to asbestos, and exposure to other cancer-causing agents in the workplace. Considering these risks, I am most concerned about my family history of lung cancer. My grandmother died of lung cancer at the age of 57. She smoked for over 35 years, and they believe that was the cause. I don’t smoke, but my risk is still elevated because of the family history, and there is really no way to prove that the smoking was the cause (my grandmother could have just had the genes needed to get cancer.) I do not plan to start smoking and I continue to have routine checkups and exams. My doctors are aware of my family history so they know what where to concentrate.

Prostate Cancer

I believe I am safe on this one since I do not have one.

Skin Cancer

Skin cancer is the most common type of cancer. Certain skin cancer risk factors are related to personal behaviors and others are hereditary. Risk factors that increase the risk of skin cancer that you can do nothing about include: a family or personal history of skin cancer, having a fair skin type that sunburns easily, individuals that have moles or abnormal moles, and living in sunny or high-altitude climates. Lifestyle- related risk factors that could increase the chance of skin cancer include: excessive sun or UV light exposure (tanning beds) and a history of sunburns due to negligence. I have an olive skin color, do not burn easily, and tan very quickly when exposed to the sun, even for short periods of time. I did go thought a phase, when I was young and dumb, where I exposed my skin to a tanning bed and thought I would get a darker completion if I didn’t wear sunscreen. I am at a higher risk of getting skin cancer due to those years of excessive exposure to UV light with little to no protection. Now that I am older, I wear sunscreen religiously, even if I only plan to be outdoors for a short amount of time. I also ensure there is UV protection in my make-up. In addition, I have regular appointments to the dermatologist to ensure we keep an eye on my skin.