What Determines Gender in Humans?
Summary
In this activity students examine karyotypes from five individuals to try to identify which chromosomes determine gender in humans. By close inspection, they should notice that the number of X chromosomes does not determine gender, but that the presence or absence of a Y chromosome does. In addition, having one extra or one missing chromosome can lead to birth defects and mental retardation. Finally, the mechanism by which extra or missing chromosomes can occur is explored, namely non-disjunction. This can be used in a large lecture setting, or as an out of class homework assignment.
CollapseLearning Goals
- Students critically analyze karyotypes and determine if it is the number of X or Y chromosomes that determine gender.
- Students explain how meiotic non-disjunction can lead to extra or missing chromosomes.
Context for Use
This activity can be used in lecture, or as an out of class assignment. Students will need to understand basic cellular genetics and meiosis, specifically non-disjunction.
In lecture students are provided with a handout that has pictures of five karyotypes and a table in which to enter data for each karyotype. Similar slides are placed in a powerpoint lecture. Students are asked to fill out the table, and look for a correlation between numbers of X or Y chromosomes and gender. In lecture this exercise takes less than 10 minutes.
As an out of class assignment, students are given the same information and table. In addition, they are provided with a series of questions that walk them through the logic of identifying which chromosomes determine gender.
Description and Teaching Materials
This activity can be used in an interactive lecture, or out of class exercise.
In class, students are given a two page handout with some karyotypes and a table to fill in. The instructor then displays the same karyotypes in class, along with pictures of individuals with that karyotype (optional). The students then fill in the numbers of X, Y and autosomal chromosomes for each individual. The instructor can then ask what appears to determine gender in humans. They can also discuss what happens to individuals with missing or extra chromosomes, and how that can occur.
Out of class, students are given the same data to analyze, and the questions that the instructor would ask in class are presented in the text. There are additional links to help students understand non-disjunction. Gender out of class assignment (Microsoft Word 1MB Jul6 06) Gender lecture handout (Microsoft Word 89kB Jul6 06) Slides for lecture (PowerPoint 1MB Jul6 06) Gender Quiz (Microsoft Word 24kB Jul6 06)
Teaching Notes and Tips
I can't think of much to add. Most students know that XX are female and XY are male, but don't know that it is the presence or absence of the Y chromosome that actually determines gender. More specifically it is the SRY gene on the Y chromosome. There is an extra question on this on the out of class exercise that could be added to the in-class exercise.
Assessment
You can do formative assessment in class to see if students are answering the questions correctly through a variety of ways - collect handouts, show of hands, clickers, short quiz.
Multiple choice summative assessment questions are provided that can be used as a practice quiz or for points.
References and Resources
MERLOT description of the NOVA site on meiosis resource that is used in this activity.
The following websites can be used by students to understand non-disjunction.
- karyotypes: http://www.biology.iupui.edu/biocourses/N100/2k2humancsomaldisorders.html (link down)
- Non-disjunction (select the powerpoint slides).