Main Concepts

The degree of chromosome similarity between two species indicates the degree of their biological relationship.

Assessable Objectives

Students will...

1. actively engage in the careful analysis of chromosome banding patterns.
2. identify examples of inversion in homologous chromosomes.
3. demonstrate their understanding that degrees of similarities in chromosomes correspond to degrees of evolutionary relationship.
4. associate degrees of similarity with relative timing of evolutionary divergence.

Teaching Strategy & Preparation

This activity can be effectively and easily inserted into any one of several parts of your course. For example:

1. Following your lessons comparing hominid and ape skulls and their chronology, introducing evolution.
2. As part of your evolution unit in which you can show this as one of several independent lines of evidence pointing consistently to a conclusion of evolution in general, and/or human evolution in particular.
3. As part of your unit on molecular biology, where you can point out the striking similarities in proteins and/or DNA sequences between different species, the patterns of which closely match the degrees of relationships based on morphology.
4. As part of your unit on genetics, where you take a look at chromosomes in general, or karyotyping in particular.
5. As a very human example of the process of science (to be pointed out wherever you do this):
1. Scientists use the simplest explanation consistent with all their data (parsimony, or "Occam's Razor").
2. MILE (Multiple Independent Lines of Evidence) providing a major strength in scientific explanations.

Students may work on this independently, in pairs, or small teams (3-4), as preferred. It could even be given as a homework assignment, and discussed/reviewed the next day.

Preparation

1. Provide handout materials for every student. Print Background Information on both sides of a single sheet. Assemble and staple the 4 pages of the Activity Packet.
2. Prepare cutout pieces showing chromosomes and bullet marks for students to manipulate. These (7 pieces per envelope) should be cut out and placed in envelopes, making a classroom set of envelopes, with one envelope for each team, or each student, if preferred. You can have a lab assistant do this, or have your students do it the first time, but keep the envelope packets for re-use every period/year.

Directions

A dramatic introduction is always an impressive way to open a topic. What you do, or how you do it may depend on the context: what topic preceded this one? However, a general approach could include dressing like an old-time detective (French coat and fedora hat, or a "Sherlock Holmes" outfit). Do something to suggest the science of investigating crimes. On the other hand, given the realities of campus violence in the news, be cautious. You don't want to be too graphic or too flippant with your references to a violent act, e.g. a shooting.

However, you could have a spent bullet (obtained from police, or a firing range, or fake it!) which you could pull out of your pocket, hold up in front of the class, and ask "If this bullet was found at a crime scene, could we tell what gun it came from?" "How?" Some students will probably know that scratch marks can be compared to bullets fired from suspected guns. If not, give a brief description of how this is done, and the principles involved. Then hand out the lesson, and let them proceed on their own.

Assessment

Use some or all of the Check Questions, along with a few additional questions in a quiz to see if they fully grasp the main concept. Be sure to test for the stated Assessment Objectives

Extensions & Variations

This could be done as part a series of crime scene scenarios which serve as metaphor of science: a process of digging out clues to figure out the most likely solution to a problem. In this context, the more familiar use of fingerprint comparisons could also be discussed. An excellent online resource for various forensic ideas and materials can be found at <http://www4.d25.k12.id.us/phs/biology/forensics.html>.

A logical followup lesson would be to explore the molecular differences in beta hemoglobin from humans, apes, and other primates, as done in "Molecular Sequences & Primate Evolution" on ENSIweb. And, if not already done, do the "Hominoid Cranial Comparison" lesson, using replica skulls of hominids and apes.

References & Resources

ENSIweb is an online resource (from the Evolution and Nature of Science Institutes) which provides detailed classroom-tested lesson plans with reproducible handouts and expected outcomes. The interactive activity presented here is a variation of one of those lessons, "Chromosome Comparisons" (by ENSI teacher Beth Kramer), at <http://www.indiana.edu/~ensiweb/lessons/chromcom.html>, and a similar lesson by ENSI teacher Larry Flammer: "Chromosome Clues" in the PBS/WGBH-Evolution Teacher's Guide (page 24), available free from <http://www.pbs.org/evolution>.

Bibliography

Alberts, Bruce, et al. 1989. Molecular Biology of the Cell. Garland Publishers. Chiasmata, p.848, fig. 15-11.

Flammer, Larry. 1983. "Karyotype Komparison." Classroom activity.

Klein, Richard G. 1999. The Human Career. University of Chicago Press. Page 71.

Kramer, Beth. 1995. "Comparison of Human and Chimpanzee Chromosomes". Classroom activity.

Wallace, B. 1966. Chromosomes, Giant Molecules, and Evolution. New York: W.W. Norton & Co., Ch.2.

Yunis, J.J. and O. Prakash, 1982. "The origin of man: A chromosomal pictorial legacy". Science, 215, 1525-1529.