Name: Per: Genetics Test Review Task: To create a model that explains how bi-racial parents can have black and white twins Part 1: DNA to Protein to Trait LT15 (Protein and Traits) - Proteins express inherited traits and carry out most cell functions. LT16 (DNA Structure) Describe structure and function and replication of DNA LT17 (Protein Synthesis) Explain the process of protein synthesis LT18 (Chromosomes) Describe the structure and function of chromosomes (combine with 16?) This section of your poster will model how each of the two parents, based on their DNA sequences, have dark skin. You will use the cell model below (the very last page or your teacher will show this to you!) for the following steps. For the sake of this model, assume that there are only two genes that control skin color (there are actually at least five) and that each gene has two alleles. You are also assuming that with respect to skin color, the two parents are genetically identical. One of these genes is the MCIR gene that controls that type of melanin produced in skin cells. o One allele produces eumelanin, a brown/black protein. o The other allele codes for the production of pheomelanin, a beige (very light brown) protein The other of these genes is called the KITLG gene, which controls the amount of melanin produced o One allele produces high levels of both types of melanin o The other allele produces low levels of melanin STEP 1: In the nucleus draw two pair of homologous chromosomes in prophase I of meiosis. These represent the chromosomes for both parents. STEP 2: For the First pair: a. Label one with an E this represents the eumelanin allele b. Label the other one with a P this represents the light skin color allele and codes for nonfunctional melanin (pheomelanin) STEP 3: For the second pair: c. Label one with an H this represents the allele that codes for high levels of melanin d. Label the other one with an h this represents the allele that codes for low levels of melanin As a pair AND individual, answer all of the following questions: What are the genotypes of both parents? What are the phenotypes of both parents? 1
Answer Explain whether or not skin color is a polygenic trait. Explain whether the MCIR gene and KITLG gene exhibit complete dominance, incomplete dominance or co-codominance. Step 4: In the nucleus, draw (by zooming in) a section of the DNA from each for the homologous chromosomes that contain the MCIR gene e. Sense Strand for E allele: AATCCGTCAGCG f. Sense strand for P allele: AATCGGTCAGCG As a pair AND individual, answer all of the following questions: If all humans started out only having the E allele (producing eumelanin), explain how the P allele arose. What type of mutation is this? In what type of cells must this mutation have arisen to be passed down to future generations? STEP 5: In the nucleus, show transcription of each allele g. Show each mrna transcript leaving the nucleus and moving to different ribosomes h. Show each mrna being translated at the ribosome. Honors: be sure to include the role of trna in transcription i. Draw eumelanin and pheomelanin being produced at the corresponding ribosome. Pick different shapes for each and either color these in accordingly or state their color alongside. STEP 6: For the proteins that control the amount of melanin produced, do not draw the sequences nor take these genes through protein synthesis. Rather, draw these proteins in the cytoplasm (where they are produced), and draw an arrow from the proteins to the nucleus to indicate where they perform their function of influencing the amount of melanin produced. Indicate on your diagram their effect on melanin production. 2
As a pair AND individual, answer all of the following questions: Explain the color of skin in both parents by addressing the relationship between DNA, chromosomes, alleles, proteins, and traits. Teacher sign off 3
Part 2: Meiosis, Inheritance, and Variation LT19 (Meiosis) Explain the possible allele combinations in an egg or sperm through meiosis LT20 (Punnett Squares) Explain the outcomes of genetic crosses LT21 (Variation) Explain that mutation and recombination increases variation This section of your poster will model how these two parents, based on their homologous chromosomes, can produce a variety of different gametes, which, through fertilization, can result in twins with dramatically different skin colors. 1. First decide whether your diagram below will represent a cell in a testicle producing sperm or a cell in an ovary producing eggs. Your partner will have the other option. Record your sex cell type here: 2. In the first circle, draw the homologous chromosomes and label the homologous chromosomes and sister chromatids with the same alleles from part 1. This circle represents the nucleus of a cell in the in either the father s testicle that will produce sperm or a cell in the mother s ovaries (remember they have the same genotypes). 3. In the second set of circles, draw the two options that exist for how the homologous chromosomes can line up in metaphase 1 of meiosis. 4. In the third set of circles, draw what the gametes will look like at the end of meiosis. 5. Circle the gamete that likely underwent fertilization to become the white twin. Record the genotype of the white twin by combining the genotypes from the gametes you and your partner circled: What process does combining these genotypes model? 6. Circle the gametes that likely underwent fertilization to become the black twin. Record the genotype of the white twin by combining the genotypes from the gametes you and your partner circled: Teacher sign off 4
As a pair AND individual, answer all of the following questions: Create a Punnett Square (dihybrid cross) from the genotypes of the parents for the two genes controlling skin color in this model. What are possible phenotypes from this couple? What are the chances that this couple would have had a white child? What are the chances that this couple would have had a black child? What are the chances that they would have had a black and white child? What are the two sources of variation presented in this model? Explain how each contributed to variation in the offspring. 1. 2. 5
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