Genetics and human traits: How do they know?

Transcription

1 LABORATORY 6 Genetics and human traits: How do they know? Cells, as the most basic unit of life, replicate themselves and in so doing provide the information and materials necessary for the development, growth and survival of the entire organism. So far this term we have learned how to use a microscope and identify organic molecules important for living organisms. We have used the scientific method to observe and compare the various conditions that cells require for growth. We can understand the roll of inheritance in the simple outward appearance of organisms as Mendel did some 150 years ago. We will see why Mendel s work was unaccepted by the scientific community and why it took a STUDENT named Sutton to take his work off the shelf and help us understand the role of replication in scientific studies. We will use the same tools Sutton used in 1902 to physically see what Mendel never observed but used math to figure out. Next week we will use this information to solve a DNA mystery using biotechnology and take a closer look at human genetics since Mendel. In this lab we will: Practice using genetic terminology such as phenotype, genotype, homozygous, heterozygous, and recessive vs. dominant Create Punnett Squares and experience Mendel s two principles. Figure out how to calculate ratios and gain an appreciation for sample size in experimentation Look at the distribution of dominant and recessive traits in a population MENDELIAN GENETICS AND SAMPLE SIZE Monohybrid Cross Working in pairs, you and your partner should have two ears of corn and two pins. You will need to keep track of the kernels you count and record your data and that of your colleagues on the data sheet at the end of the exercise. One ear of corn signifies the Monohybrid condition; it is an example of how many traits? That trait is What are the two possibilities? and 6-1

2 How many alleles are associated with that trait? alleles Stick the pin in a kernel on the left side of the ear and count 4 rows, keeping track of the trait of interest. Record your data at the front of the room being sure to include the ratio from your data sheet at the end of this exercise. What was Mendel s phenotype ratio for this condition? What was yours? What principle did Mendel identify with this condition? Record the outcome of your table and finally the outcome of the class. How does ratio change with sample size? What are the phenotypes? and Use the punnett square below to help you determine the phenotype and genotype ratio of the corn Punnett Square Dihybrid Cross Now, complete the same task with the Dihybrid Corn. How many traits will you be counting? How many alleles? How many possible phenotypes are there? What are the possible phenotypes? 6-2

3 What are the possible genotypes? What principle did Mendel identify with this condition? What phenotype ratio did you and your partner calculate? What ratio did your table calculate? What ratio was the class total? What is the genotype of each of the numbers in the ratio? Human Genetic Traits Mendel chose traits the were controlled by two alleles. Choosing traits with 2 possibilities (this or that) simplifies the understanding of genetic inheritance. There are some human traits that demonstrate the dominant-recessive behavior we saw demonstrated with the monohybrid corn. Use the table on the last page of this exercise to determine your phenotype and possible genotype. Your instructor will survey the class and work with you to estimate the percentage of students in the class with each trait. 1. For each trait, is the dominant phenotype always more prevelant among class members? 2. If the class was representative of the general population, what can you conclude about the relationship between dominant and recessive phenotypes and their frequencies in the population? 3. Jenie and Brad both have free earlobes. What are their possible genotype(s)? What is the probablity that they will have a child who as attached earlobes? If they have had two boys, what is the probablity that the next child will have free earlobes? 6-3

4 Monohybrid Dihybrid 6-4

5 Human Trait Your Phenotype Your Genotype Class % Widow s peak hairline Straight hairline (recessive) Free earlobes Attached earlobes (recessive) Tongue rolling Non tongue rolling (recessive) Mid-digital hair No mid-digital hair (recessive) Normal thumb Hitchhiker s thumb(recessive) 6-5