1615 Lab 10 Genetics worksheet1

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Dec 6, 2023

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Mendelian Genetics Objectives : At the end of this lab, you should be able to: 1. Define and use the following terms: gene, allele, dominant, recessive, genotype, phenotype, homologous chromosomes, homozygous, and heterozygous. 2. Define and explain Mendel’s principle of segregation. 3. Predict the genotype of the parental generation, if given the phenotype. 4. Solve problems involving monohybrid and dihybrid crosses. Introduction Diploid cells contain two sets of homologous chromosomes . One set (or one chromosome in a pair) comes from one parent while the other set comes from the other parent. Genes , found on homologous chromosomes, contain information that governs the same traits. For example, in pea plants, seed color is determined by one gene ‘C’ which can have various forms, such as C or c . Each different form of a gene is called an allele . Every diploid cell has two copies of a gene, one on each member of the pair of homologous chromosomes. The genetic makeup of a cell is called its genotype. If a cell possesses two copies of the same allele, then the cell is said to be homozygous ( CC or cc ) for that gene. If the cells possess two different alleles, for a gene, then the cells are said to be heterozygous ( Cc ). All somatic cells (those which divide by mitosis), from the same organism, have the same genotype. In pea plants, the C allele is dominant over c ; in other words, when C is present, it masks the c allele. The c allele is referred to as recessive . Capital letters represent the dominant allele while lowercase letters represent the recessive allele. For example: Yellow ( C ) seed color is dominant over green ( c ) seed color. A CC or Cc genotype would result in yellow seed color, which is dominant. A cc genotype would result in green seed color, which is recessive. The outward manifestation of a genotype is called its phenotype . Exercise 1: Taste Test Things taste differently to different people. The ability to taste sodium benzoate and phenylthiocarbamide (PTC) is inherited. Sodium benzoate, once used as a food preservative, tastes differently to various people. The ability to taste PTC is due to the presence of the dominant allele (T), located on chromosome 7. Those unable to taste PTC possess the recessive allele (t). PTC is detected by taste buds located at the back of the tongue and throat resulting in a bitter taste. However, there are many different types of taste buds, which can interpret bitter flavors. Because of this, not everyone can detect the presence of PTC. In this exercise, you would investigate the genetically controlled trait of taste; your classroom would be your sample population. You would test your ability to taste PTC and sodium benzoate, and then you would compare your results with your group and the class. In this experiment, you would use three different kinds of test paper:  Control test paper (C) : You should only taste the paper. This prevents confusion later on when testing the other papers so that you know whether you are tasting paper or chemical.  PTC test paper (#1) : If you experience a bitter taste, when the PTC paper is in your mouth, then you possess the dominant allele. If the paper tastes like the control, then you possess the recessive allele.  Sodium benzoate test paper (#2) : The most common reactions to sodium benzoate are a sweet, salty, or bitter flavor, although some people indicate other or no response at all. 1

1. Use forceps to acquire a square piece of each test paper. 2. Testing each paper, one at a time, place the paper on your tongue and move it around to be sure the PTC or sodium benzoate becomes well mixed with your saliva. 3. Discard the paper and record your reactions in Tables 1 and 2 of your lab report. 5. In your lab report calculate the totals of your lab group and the class. Also, determine the total % of tasters and non-tasters in the class. The video lecture for this lab has provided you with MOCK DATA to enter into your lab worksheet. Be sure to use that data and to answer the remaining questions for Exercise 1 based on the numbers provided Exercise 2: Mendelian genetics Activity A: Plant Sprouts You will be investigating the properties of plant sprouts. Plants have more characteristics than just color, investigate all the characteristics of the plant sprouts in the pictures on Canvas. Plant pictures are in the Module on Canvas Activity B: Corn Zea mays , commonly referred to as corn in the United States, is one of the most important food crops in the world. Because of its economic importance, corn’s genetics have been well studied. Corn has 10 pairs of chromosomes, with one set inherited from the “male” and the other set from the “female”. In corn, the color of the kernel is determined by the color of the aleurone (see figure 1 below). If the aleurone is colorless, the kernel will appear yellow or white which is the color of the endosperm. Figure 1: Diagram of the layers of a corn kernel

In this exercise, you will study several corn phenotypes that are expressed in the seed. You will be given a picture of an ear of corn. You can find this picture on the Modules page of Canvas. Each seed on an ear of corn is due to a separate fertilization event. You will analyze corn with purple and yellow kernels. Additionally, you will analyze a gene that makes the seeds wrinkled or smooth, depending on the sugar content of the endosperm. Normal endosperm is rich in amylase starch. A recessive gene produces endosperm with high sugar content. In these kernels, as the corn dries, the endosperm loses water and the seeds wrinkle. Activity A: Plant Sprouts 1. You will find a PDF with animated pictures of plant sprouts on the Modules tab of your Canvas Page. 2. There are many differences between individual plants, however this demonstration only focuses on stem color. Notice that different groups have different proportions of plants with purple vs white stems. 3. Figure out if the Mendelian cross is monohybrid or dihybrid. Also, figure out which groups are the parental generation, which one is the F1 and which one is the F2. Activity B: Corn 1. Examine the ear of corn which is pictured. Answer question 1. This corn belongs to the F 2 generation ; in this exercise, you will analyze the phenotypes and genotypes of a dihybrid cross . 2. Count the number of kernels (for each one of the phenotypes ) using only two rows of your corn and record the data. Calculate the ratio of each of the phenotypes by taking the number of kernels for that phenotype and dividing by the total number of kernels counted. 3. Class data has been provided in the table for number 3 of activity B. Use this data to complete the remaining portions of the tables. 3

Lab 10: Mendelian Genetics Name Lab Section 210 Date 11/6/2020 T Exercise 1: Taste Test (data provided in video) 1. Record the reactions of the test paper (1pt). PTC taste test Lab group taste totals Class taste totals % Tasters and Non-tasters Taste 3 17 70.83% Non-taste 1 7 29.17% 2. Fill in the table below (1 pt). Sodium Benzoate Lab group taste totals Class taste totals % Tasters and Non-tasters Sweet 1 6 25% Salty 2 11 45.83% Bitter 0 4 16.67% Other 0 1 4.17% Non-taste 1 2 8.33% 3. What are the phenotypic ratios for the PTC and sodium benzoate test (2 pt)? 70% of the class could taste the PTC vs 92% that could tast something from the Sodium Benzoate test. 4. Is the ability to taste a bitter flavor on PTC paper dominant or recessive? Explain. (2 pts) It is dominate. If it was recessive there would be fewer of the class that would be able to taste it, which means that it has to be a trait that is passed on and shows more often. 5. What conclusions can you make regarding the genetics relating to Sodium Benzoate? Is there a clear dominant/ recessive trait? (2 pts) It looks like salty was the highest, but I don’t think there is a clear absolute dominant and recessive trait for it. 4

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