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Genes and Proteins

Investigation 3 – PreLab









Plant scientists use gene modification techniques to develop improved crop varieties such as drought-tolerant maize.


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

  • Why can mutations in the DNA of a single cell affect the functions of an entire organism? 

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 concept  as a class:

  • DNA is found inside almost all cells in the body.
  • DNA is located in the nucleus of cells in special structures called chromosomes.
  • The DNA of a chromosome contains many genes.
  • Each body cell has two copies of each chromosome in its nucleus. The copies are called homologous chromosomes.
  • In body cells, each chromosome in a homologous chromosome pair came from a different parent (one from the father and one from the mother).
  • Homologous chromosomes contain the same genes, but they are not identical. They may contain different alleles or versions of the genes. 
  • Cells in the body can divide and produce new cells. They do this through a process called the cell cycle.
  • The first part of the cell cycle called interphase. The cells grow larger and all of the chromosomes are duplicated. Each homologous chromosome in a pair is copied. The two identical copies of each chromosome are called sister chromatids. They are attached together by a structure called the centromere.
  • The second part of the cell cycle is called mitosis. The four phases of mitosis are prophase, metaphase, anaphase, and telophase.



  • chromosome
  • mitosis

Note: Definitions of these terms can be found on the Introduction page to the CELL.

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 Ask Why section in your SDR. 

  • Why do body cells divide?
  • How do body cells divide?
  • When body cells divide, how do the new cells get the same amount and type of DNA as the original cells?

Note: In addition to the Key Terms above, the following terms will be defined for you in Backgrounds throughout the Investigation: homologous chromosome, allele, sister chromatids, and centromere. You should review these vocabulary terms before the Investigation begins.

  • Review the following:
  • Each cell goes through a cycle with a beginning and an end that repeats. Cells go through this cycle so that they can divide and form two new cells. The central portion of the cell cycle is mitosis, during which time the chromosomes separate.
  • Before mitosis begins during interphase, each cell has two copies of each chromosome called homologous chromosomes. During interphase, cells grow larger and all the chromosomes are copied (duplicated) resulting in two copies of each.
  • Mitosis begins with the first of four phases. The four phases are: prophase, metaphase, anaphase, and telophase.
  • In prophase, the chromosomes condense into rod-like structures that can be seen under the microscope and the nuclear membrane dissolves.
  • In metaphase, duplicated chromosomes line up with the centromeres on spindle fibers in the center of the cells.
  • In anaphase, the sister chromatids separate and move down the spindle fibers to opposite ends of the cell.
  • In telophase, the chromatids move to the ends of the spindle fibers. The spindle fibers disappear and new nuclear membranes form around each set of chromosomes.
  • The cell next will divide and each new cell will have identical sets of chromosomes in its nucleus.
  • In this Investigation, you will model the different phases of mitosis. You will also view cells undergoing mitosis under the microscope.
  • Play the video below. Remember to follow along with your SDR and make any notes that you think might be helpful in the lab.
  • After the video, divide into your 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.