Unit II Assignment—Genetics Worksheet
Gregor Mendel ’s Experiments, Theories, and Findings
1. “Mendel observed that pea plants had traits, such as color, that were either “one or the other,” never something in between. In your own words , 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.)
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Response
Mendel concluded that given factors control particular traits, which he stated as a gene being the outcome. Every factor has two varied forms defined as an allele. For instance, two alleles control the plant color, x for dark red and X for gray. x is termed recessive, while X is dominant. Thus, when xx dark red and XX gray are crossed, the outcome is Xx heterozygous gray. The alleles do not blend even if they remain together. It is noteworthy that segregate gametes could have an x allele or X allele at meiosis. Such a situation is why the pea plants' traits are in one or a different form.
2. 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.
In your own words , 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.)
Response
A single gene comprised of two alleles determines the two colors. The two alleles are y and Y. The allele Y is considered dominant and stands for the color yellow, and the recessive allele y stands for the color green. The dominant allele often takes precedence over the recessive allele's effect in heterozygous situations, and what is expressed is the dominant phenotype. The recessive y allele is suppressed by the dominant allele Y. Therefore, what appears in F1 is the color yellow.
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. 3. 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 Genotype of parents: _GG_ x _gg_
| Parent #1 | |||
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Parent #2 |
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| Gg | Gg | ||
| Gg | Gg | ||
What is the genotypic ratio of the offspring in Question 3? 100% What is the phenotypic ratio of the offspring in Question 3? 4 green kernels
4. Yellow seeds are dominant over green seeds in pea plants. Cross a heterozygous (yellow seeded) plant with a green seeded plant.
Key: __X to represent yellow seed ____x to represent green seed____ Genotype of parents: ____Xx______ x _____xx_____
| Parent #1 | |||
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Parent #2 |
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| Xx | xx | ||
| Xx | xx | ||
What is the genotypic ratio of the offspring in Question 4? 50% Xx, 50%xx or 2Xx 2yy What is the phenotypic ratio of the offspring in Question 4? 2 green/ 2 yellow
5. Now cross two of the heterozygous F1 offspring from question #2.
| Parent #1 | |||
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Parent #2 |
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| YY | Yy | ||
| Yy | yy | ||
What is the genotypic ratio of the offspring in Question 5? 25%yy 50yy 25%YY What is the phenotypic ratio of the offspring in Question 5? 1 green/ 3 yellow
6 . 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)
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Table 1 |
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| Heads/heads (hh) | 26% |
| Head/tails (ht) | 40% |
| Tails/tails (tt) | 34% |
| Ratio (hh:ht:tt) | 26:40:34 |
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?
Response The ratios as seen in percentages, are almost equal. 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.)
Response
Doing more coin flips would lead to closeness in percentages from question #5.
Cancer Risk Factors
6. 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 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)
Response
People are subject to various conditions that lead to cancer forms in the body. The types of cancers well known include skin cancer, prostate cancer, lung cancer, rectal and colon cancer, and breast cancer. Breast cancer is caused due to gene mutation common in women. Risk factors are inability to breastfeed, failure to have children, inactivity, being overweight, and drinking alcohol. The best way to reduce the risk factors includes having genetic counseling sessions and testing, undergoing preventive surgery, and having medication such as raloxifene and tamoxifen. Colon and rectal cancer is also termed as colorectal cancer. The risk factors of colorectal cancer include failure to exercise while aging and inflammatory bowel disease, including ulcerative colitis or Crohn's disease. Hereditary factors could also be a risk factor. The ways to decrease the risk factors associated with colorectal cancer include exercising, eating lots of vegetables, and getting frequent screening sessions. Lung cancer is related to the risk factors such as exposure to tobacco smoke, secondhand smoke exposure, exposure to asbestos, and other radioactive ores. The ways to decrease such risk factors include avoiding exposure to smoking, secondhand smoke, asbestos, and other radioactive ores. The fourth type is prostate cancer. The risk factors include gene changes, family history, age, diet, obesity, smoking, chemical exposure, sexually transmitted infections, and vasectomy. The best way to prevent these risks includes being physically active, getting healthy while having a healthy eating pattern, and taking prescribed medications. Skin cancer include risk factors such as sun exposure, suppressed immune system, precancerous skin conditions, inherited syndromes, gender, age, human papillomavirus, and past radiation therapy treatments. Ways to reduce such risk factors include limiting sun exposure, having sun-protective clothing, examine skin regularly, and use proper medication such as nicotinamide. Individuals should also avoid using UV tanning beds. They should instead use broad-spectrum sunscreen.
