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X or Y: Does It Make a Difference?

X or Y: Does It Make a Difference?

Normal human genes: Male XY genes (left); Female genes XX genes (right).
© Wessex Regional Genetics Centre/Wellcome Images. CC-BY-NC-ND 4.0

  • Grades:
  • Length: 60 Minutes


Students describe the functional differences of X and Y chromosomes, and explain the significance of these differences within the human genome.

Teacher Background

Detailed studies of the sequence and gene activity within the human X chromosome are providing interesting insights and raising questions about the differences between males and females. Women have two X chromosomes while men have an X and Y. The Y chromosome is relatively gene-poor. In women, one of the X chromosomes is partially shut down in each cell. Adding additional interest to the picture is that more than 300 diseases have already been associated with the X chromosome.

Objectives and Standards

The Cell

  • Cells store and use information to guide their functions.

  • Cell functions are regulated through selective expression of individual genes.

Molecular Basis of Heredity

  • Instructions for specifying the characteristics of the organism are carried in DNA.

  • There is a pair of chromosomes that determines sex.

Materials and Setup

Teacher Materials (see Setup)

  • Computer, projector and projection screen 

  • PowerPoint® slides number 8 "The Human Genome," and number 14, "Regulation of the Human Genome (IV)," from the slide set "Molecular Basis of Heredity: Part 2. Genomes."

  • Overhead projector (optional, see Setup)

  • Transparencies of slides (optional)

Materials per Group of Students

  • Computer access for each group member, with four different articles per group preloaded, OR one set of articles listed below (see Setup)

Materials per Student

  • Copy of "Category Notes" and "3-2-1" student sheets


  1. Prepare to project the slides (see Teacher Materials, above) from a computer OR make transparencies of the slides and use an overhead projector.

  2. Each student group member will read a different article (below). Have students read the articles online, OR make a photocopied set for each group and distribute before beginning the activity.

  3. If students will read the articles online, pre-load the articles before class.

Procedure and Extensions


  1. Begin a class discussion. Ask students, What do you know about the X and Y chromosomes in humans?

  2. Have students record at least one question they have about the X and Y chromosomes in the space provided on the "Category Notes" page.

  3. Project and discuss the slide, "The Human Genome," followed by the slide, "Regulation of the Human Genome IV."

  4. Prompt students to add notes to the first column of their "Category Notes" page.


Divide students into groups of four. Have each student group member to read a different article, either online or a photocopied version (see Setup).


Distribute and ask each student to complete the "3, 2, 1" activity sheet. Have students list three things they learned, two things that surprised them, and one new question they have after reading their articles.


As a group or class, decide on and add information to the second column of the notes.


Ask each student to highlight the most important information in the first two columns of the "Category Notes" page. In the third column, have each student explain the significance of the highlighted information he or she chose.


  • Not all animals have the same genetic strategy for determining sex. Have students read and then discuss the  article, "Duck-billed Platypus Boasts Ten Sex Chromosomes." Oct. 25, 2004, Nature News.

  • Have students investigate other organisms. This is a great time to discuss adaptation and evolutionary successes. For example, ask students, Why is there an evolutionary advantage to having two sexes?

Handouts and Downloads

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