Thinking Like a Scientist Activity 3
Scientists themselves believe, at heart, that behind the diversity
lies a unity.
--Horace Freeland Judson
Order from Disorder
Students will investigate the importance of comparison and classification
About the Activity
When scientists describe and classify objects or events, they do so in
order to compare and communicate information about the objects or events.
By comparing different groups or classifications, scientists can begin to
recognize patterns. These patterns help scientists draw conclusions about
the properties and relationships between the objects or events.
In this activity, students will create a karyotype--an ordered display
of chromosomes--to see one of the patterns that occurs in living organisms.
To study a person's chromosomes, scientists take a photograph of a sample
of white blood cells under a microscope. Water and fixatives are added to
the cell during the metaphase cycle of mitosis, when the chromosomes are
spread out. This allows the scientists to clearly see each chromosome as
well as the location of the centromere of each chromosome. The chromosomes
are often treated with a chemical stain, which stains some segments more
darkly than others. This results in a distinct banding pattern. Scientists
then cut up the photograph and make a chart called a karyotype that shows
the individual chromosomes grouped in pairs. The chart helps scientists
see defects in the chromosomes and/or any missing or extra chromosomes.
For each group:
Duplicate the handout to distribute to the students. You may also want
to provide a second copy, or make an overhead transparency, of the handout
so that students have a completed karyotype to examine.
- Have students begin by cutting out the individual chromosomes on the
handout. They should then place all the cutout chromosomes in a pile, and
mix them up.
- Have students create the karyotype by regrouping the chromosomes into
pairs based on length, banding pattern, and position of centromere. Ask
them to tape or glue each pair onto the sheet of paper. Then have them
label the pairs with the names of the chromosomes.
- What is the normal number of chromosomes in a human body cell? How
do you think scientists could have determined this?
- How might scientists be able to identify possible genetic defects by
creating a karyotype?
- Is this a karyotype for a male or a female? How can you tell?
- There are normally 23 chromosomes in human sperm and egg cells. Why
is the number of chromosomes in these cells different from those in human
Handout 1: Human Chromosomes
Activity 4: Seeking Solutions