Mendelian Genetics (Jarrod Parra)
Title:
Genetics with a Smile! :)
Principle(s) Investigated:
Mendelian genetics is based on discoveries made by Gregor Johann Mendel in the mid-1800s. Mendel’s discoveries led to his theories on inheritance—including three laws. His first law, the “Law of Segregation,” states that every individual possesses a pair of alleles (an alternative form of the same gene) for any particular trait, and that each parent passes a randomly selected copy (allele) to its offspring. Mendel’s second law, the “Law of Independent Assortment”—also known as "Inheritance Law”—states that separate genes for separate traits are passed independently of one another from parents to offspring. Lastly, Mendel’s third law, the “Law of Dominance,” states that recessive alleles will always be masked by dominant alleles. Mendel's findings allowed other scientists to predict the expression of traits on the basis of mathematical probabilities. Mendel's experiments with mixing one trait always resulted in a 3:1 ratio between dominant and recessive phenotypes.
Materials:
Worksheets, colored pencils, and coins
Procedure:
1. Obtain two coins from your teacher.
2. Use one coin for the “mother” and the other coin for the “father” to represent each of the parents.
3. Flip the coins for each parent and each trait.
4. If the coin lands heads up, it represents a dominant allele. A coin that lands tails up indicates a recessive allele.
5. Record the result for each person by circling the correct letter on the worksheet.
6. Use the results and the “Smiley Face Traits” page to determine the genotype and phenotype for each trait.
7. Create your Smiley Face.
8. To determine the sex of your smiley face, flip the coin for the male parent. Heads will represent X, while tails will represent Y.
Student prior knowledge:
The student should have at least a very basic understanding of cellular structure and functions, DNA, RNA, mRNA, tRNA, transcription, and translation.
Questions & Answers:
1. Why did you only need to flip the male parent coin to determine the sex of your smiley face? Since the female always contributes an X chromosome, the male determines if the smiley face will be female or male by contributing either an X or a Y chromosome.
2. How would the smiley faces change if one of the parents were homozygous dominant for all the traits, while the other was heterozygous? The recessive traits would not be observed in any of the smiley faces.
3. How would the smiley faces change if one of the parents were homozygous recessive for all the traits, while the other was heterozygous for all traits? The recessive traits would be observed more often than if both parents were heterozygous.
Applications to Everyday Life:
1. Hemophilia—the body’s in ability to clot blood—is a recessive allele disorder. A recessive allele disorder rarely occurs since it is dependent on the crossing of two heterozygous parent cells. This disorder has affected much of the European royalty in history, such as Queen Victoria of Great Britain.
2. Albinism is a congenital disorder characterized by the complete or partial absence of pigment in the skin, hair, and eyes due to absence or deficiency of tyrosinase, a copper-containing enzyme involved in the production of melanin. Albinism results from inheritance of recessive alleles, and is known to affect all vertebrates, including humans.
3. Sickle-cell disease is a hereditary blood disorder, characterized by red blood cells that take an abnormal “sickle” shape. Sickling decreases the cells flexibility and results in a risk of various life-threatening complications. This sickling occurs because of a mutation in the hemoglobin gene. Individuals with one copy of this defective gene exhibit both normal and abnormal hemoglobin. This is an example of codominance.
http://sitemaker.umich.edu/darcyholoweski/files/rwt-6-genetics-with-smile-3_8-2ance.