Activity 2: Genetic Inheritance
Students will model inheritance patterns in humans to compare the difference
between genotypes and phenotypes.
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
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
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:
- 2 coins
Duplicate Handouts and distribute to pairs of students.
- 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
- 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.
- Have students use the profile they created to answer the questions
on Genetic Profile Worksheet.
- 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?
- 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?
- 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?
- 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?
- 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