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Investigation 1 – PreLab









The planet we live on is constantly changing. To survive and reproduce, all living organisms must adjust to these changes. If organisms are not able to adapt to changing environmental factors — including competition for resources, predation, infectious diseases, and climate – they may not survive.


Evolutionary biologists seek to understand the origin of organisms, their genetic variations over time, and how they are currently adapting. They might try to discover the earliest ancestors of modern humans. Or he or she may analyze a flu virus to understand how it develops resistance to vaccines.


This Investigation is designed to help you to answer the following Focus Questions:

  • Why do individuals of a species have different traits?
  • What is the relationship between the survival of the individuals of a species and genetic variations?

Note: This question is located in your SDR at the beginning and end of the Investigation.


As a class, read the Background(s) in the Investigation. When finished, discuss the following concepts as a class:

  • Many species have developed traits that allow them to survive in a particular environment. These traits are often called adaptations.
  • Not all individual organisms of a species that live in an environment have exactly the same trait or adaptation. The difference of traits is described as variation.
  • Genes are the building blocks for the specific traits that allow organisms to adapt to their environment.
  • A trait is any genetically inherited feature of an organism, such as eye color.
  • These traits are coded for by genes.
  • In all organisms, there is more than one possible form for each gene. Each possible form is called an allele.
  • The differences in the forms of a gene are described as genetic variation.
  • Genes are often made up of two alleles that have a special relationship with each other.  
  • The DNA of most cells of an organism has two copies of a gene or two alleles. One allele is from the father and one is from the mother.
  •  A recessive allele is one that is displayed only when there is no dominant allele. 
  • The combination of alleles in an organism is called its genotype.
  • The form or variation of the trait that results from the combination of alleles is called its phenotype.
  • Differences in the genotype are described as genetic variation. These can lead to differences in the phenotype which are described as variations of a trait that you can observe.
  • When the two alleles are the same (either both are dominant or both are recessive) the genotype is said to be homozygous.
  • When the two alleles are different (one is dominant and one is recessive), the genotype is said to be heterozygous.
  • When organisms reproduce, one allele comes from the mother and one comes from the father. This process occurs at random so that either allele can be passed on to the offspring. There are then many possible combinations of alleles.



The following list includes Key Terms that are introduced in the Investigation Background(s). They should be used, as appropriate, by teachers and students during everyday classroom discourse.

  • species
  • trait
  • genetic variation
  • adaptation
  • environment
  • allele
  • dominant
  • recessive
  • genotype
  • phenotype

Note: Additional words may be bolded within the Background(s). These words are not Key Terms and are strictly emphasized for exposure at this time.


  • Complete the Recall section in your SDR. 
  • Are all members of a species exactly alike?
  • How do the traits or adaptations that animals and plants have help them survive in their environments?
  • Does variation in traits permit the survival of individuals in a species?
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful.
  • After the video, divide into lab groups to discuss strategy for the lab. For example, you may assign certain group members to perform specific functions during the lab.

Note: The purpose of the video is to allow you to anticipate the laboratory experience you will soon encounter. You should leave this PreLab session with a firm idea of what to expect and how to perform in the lab.

Note: Homework is posted below the video.



You should review the Investigation and video in preparation for the Lab.