Note to teacher: Have students read through the first two sections of Background Information, Mitosis and Growth and Human Chromosomes, and review the questions and answers provided for each section to ensure understanding.

GET FOCUSED

Mitosis is the process that cells use to make exact copies of themselves. It happens so our bodies can grow, repair injuries, and replace old or damaged cells. During mitosis, one cell divides to form two new cells, each with the same number of chromosomes (genetic information in the form of DNA) as the original. The process has several steps: the DNA is copied, the chromosomes line up in the middle, they are pulled apart, and then the cell splits into two. This way, every new cell has the same exact instructions to do its job in the body!

Inform students that the Investigation is designed to help them to answer the following questions:

• What are the major differences between asexual and sexual reproduction? In your answer, describe both the advantages and disadvantages of asexual and sexual reproduction. Do humans reproduce asexually or sexually?
• Why is it important that each new cell gets an exact copy of the DNA during mitosis?
• How do chromosomes ensure that genetic information is accurately passed from one cell to another during cell division?
• How does mitosis help organisms grow and heal?

GO DEEPER

As a class or independently as homework, have students read the first two sections of the Background Information section, Reproduction and Growth and Human Chromosomes.

Extended answers to the following questions are found on the Teacher Portal PostLab page. Go over these concepts and questions as a class prior to the lab to encourage students to look for answers as they proceed through the Lab and PostLab. In PostLab, you may review the questions again to address any misconceptions.

Mitosis and Meiosis

• What is the primary purpose of mitosis?
• What is the number of daughter cells produced in mitosis?
• How does the chromosome number of daughter cells compare to the parent cell in mitosis?
• In which types of cells does mitosis occur?
• What are the main stages of mitosis?
• Why is maintaining the full chromosome number important in mitosis?
• Summarize the functions of mitosis in one sentence.

Human Chromosomes

• How many chromosomes are found in almost every human cell, and how are they organized?
• Where do humans inherit their chromosomes from, and how is this reflected in chromosome pairs?

• How is the 23rd pair of chromosomes different between males and females?
• Where do humans inherit their chromosomes, and how is this reflected in chromosome pairs?
• What is the significance of organizing chromosomes into pairs for scientific studies?
• How do scientists use high-magnification slides to study chromosomes, and what can they learn from them?

Note: These concepts are integrated into the Student Guide Backgrounds and CELL Introduction and are used to deepen students’ comprehension of the big ideas. You will find succinct answers to these questions in the PostLab; reading through these questions in PreLab will help students focus on important information during the Investigation.

LEARN THE LabLearner LINGO

The following list includes Key Terms introduced in the Investigation. Teachers and students should use them appropriately during everyday classroom discourse.

Anaphase – The third stage of mitosis where sister chromatids are pulled apart to opposite sides of the cell.

Autosomes – The 22 chromosome pairs that do not determine sex but carry genes for other traits.

Chromosomes – Structures made of DNA that carry genetic information; humans have 46 chromosomes (23 pairs).

Cytokinesis – The final step of cell division, where the cytoplasm splits, creating two separate daughter cells.

Homologous Chromosomes – Pairs of chromosomes (one from each parent) with corresponding genetic information.

Interphase – The phase of the cell cycle where the cell grows, replicates DNA, and prepares for division.

Karyotype – A visual representation of an individual’s chromosomes, used to study genetic conditions.

Meiosis – A special type of cell division that produces gametes (sperm and eggs) with half the normal chromosome number.

Metaphase – The second stage of mitosis where chromosomes align in the center of the cell.

Mitosis – A type of cell division that produces two identical daughter cells for growth and repair.

Prophase – The first stage of mitosis where chromosomes condense and spindle fibers begin to form.

Sex Chromosomes – The 23rd chromosome pair that determines biological sex (XX for females, XY for males).

Sister Chromatids – Identical copies of a chromosome, connected by a centromere, that separate during cell division.

Telophase – The final stage of mitosis where two new nuclei form and the cell prepares to fully divide.