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Activity 2: Genetic Inheritance



Students will model inheritance patterns in humans to compare the difference between genotypes and phenotypes.


Background Information

The traits or characteristics of an organism are determined by genes. The gene for a particular trait can have two or more different forms, which are called alleles. For every gene, a person has two alleles, one inherited from each parent. The combination of inherited alleles represents the genetic makeup, or genotype, of the organism. The way a genotype is expressed in an organism is called its phenotype. For many traits the phenotype is a result of an interaction between the genotype and the environment.

Genotypes versus Phenotypes

guinea pigs In this example, the trait is fur color, and the alleles are B (black) and b (white).

For a specific trait, some alleles may be dominant while others may be recessive. The phenotype of a dominant allele is expressed regardless of what the other allele is, while the phenotype of a recessive allele is expressed only when both alleles are recessive. However, in some cases, one allele is not completely dominant over the other allele, and the resulting phenotype is a combination of each allele's phenotype. This is known as incomplete dominance. In addition, some traits are determined by a combination of several genes, and the resulting phenotype is determined by the final combination of alleles of all the genes that govern a particular trait.

Geneticists symbolize alleles in various ways. Often uppercase letters are used to represent dominant alleles and lowercase letters are used to represent recessive alleles. An organism that has a pair of identical alleles for a trait is said to be homozygous for that trait. Organisms that are homozygous for a dominant trait are represented by all uppercase letters (i.e., GG), while those that are homozygous for a recessive trait are represented by all lowercase letters (i.e., gg). Organisms that have different alleles for a trait are said to be heterozygous for that trait, and are represented by a combination of uppercase and lowercase letters (i.e., Gg).



For each pair of students:

  1. Handouts:
  2. 2 coins
  3. Pencil


Duplicate Handouts and distribute to pairs of students.


  1. Explain to students that they will be creating a hypothetical genetic profile of a "child" using the traits listed on Genetic Trait Chart. (Note: you may want to point out that some of the skills listed on the handout and their pattern of inheritance are hypothetical, and not necessarily inherited.) One student in each pair will represent the mother of the child, while the other student will represent the father. For each gene listed, each student should flip his or her coin. Then each pair of students will record the results of their coin flips in the genotype column on Genotype and Phenotype Record Sheet. Heads represents a dominant allele, while tails represents a recessive allele.

  2. After students have recorded the genotype for each trait, have them use Genetic Trait Chart to determine the phenotype for each trait. Remind students that some of the phenotypes are determined using one gene, while other phenotypes are determined using a combination of genes.

  3. Have students use the profile they created to answer the questions on Genetic Profile Worksheet.


Discussion Questions

  1. Discuss the answers to the questions on. What were some of the reasons you decided that certain jobs were suitable for your child? What were some of the reasons you decided that certain jobs were unsuitable for your child?

  2. If a person's genotype was not very well suited for a given career or task, what might he or she be able to do to overcome the limitation?

  3. If a person's genotype indicated that he or she had a very high predisposition to alcoholism, does this mean he or she would become an alcoholic? Why or why not? Do you think the person's employer should be given this information? Why or why not?

  4. How might having a genetic profile be helpful? How might it be a disadvantage? If a genetic profile is created, who should have access to the profile?

  5. In the simulation you just completed, you simulated the creation of possible genotypes using hypothetical traits. How is a simulation useful in helping to understand certain biological events? What are some limitations of simulations?


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