1. Activity 14
Genes and Chromosomes

3. Read the introduction.
How does the behavior of chromosomes in cells help to explain the behavior of genes that are passed from one generation to the next?
Review information from previous activities about the connection between the behavior of chromosomes in cells and the behavior of genes passed from one generation to the next. For more information on having this class discussion see the Teacher’s Edition for this activity.

4. Challenge
How do genes and chromosomes behave during meiosis and sexual reproduction?

5. Student Sheet 14.1, “Three-level Reading Guide: Genes and Chromosomes,” presents statements that require three levels of understanding. Determine which statements are supported by the text.
Students fill out the Three-level Reading Guide after completing the reading. For more information on how to support them in this, suggestions on points to emphasize after they have completed the reading, and for a sample student response to the student sheet see the Teacher’s Edition for this activity and Teacher Resources III: Literacy.

6. Crossing Over

7. Analysis 1
Explain the relationship between genes, chromosomes, and DNA.
Analysis Question 1 can be scored with the Understanding Concepts (UC) Scoring Guide. For more information and a sample student response see the Teacher’s Edition for this activity.

8. Analysis 2
A species of snail has 24 chromosomes— 12 pairs—in each somatic cell. How many chromosomes are there in a snail egg cell? A snail sperm cell?
Analysis Question 2 provides a Quick Check opportunity to make sure students understand meiosis and gamete formation.

9. Analysis 6 and 7
6. The chromosomes pictured below are from a fruit fly that is heterozygous for two traits. How many kinds of gametes could form if this were in a male? A female?
7. Consider your answer to Question 6. Explain how crossing over could affect the gametes that result.
Analysis Question 7 provides a Quick Check opportunity to make sure students understand meiosis and gamete formation.

10. Revisit the Challenge
How do genes and chromosomes behave during meiosis and sexual reproduction?
Students should be able to explain meiosis and the means by which gametes form with half the normal chromosome number. See the Teacher’s Edition for this activity for more information.

11. law of independent assortment crossing over diploid meiosis gamete
Key Vocabulary
chromosome
law of independent assortment
crossing over
diploid
meiosis
gamete
mitosis
gene
nondisjunction
haploid
somatic cell
karyotype
See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning.
Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.