Table of Contents
Ishihara Tests
Overview
In this activity, you will take four Ishihara tests. Ishihara tests are used to diagnose colorblindness. The genes encoding photoreceptor proteins for the long wave-length (reds) and middle wave-lengths (greens) reside on the X chromosome at Xq25. Since the Y-chromosome is not homologous, any mutation to either of these genes that render them non-functional results in an inability to perceive either of those colors. Men are more susceptible to the condition of red-green colorblindness since they are hemizygous. This means that there is no corresponding gene that could complement a deficient red or green photoreceptor gene.
Dr. Shinobu Ishihara published his test for color perception in 1917 and this test is widely used to detect deficits in color perception.
Materials
Each lab group will need the following:
- 4 Ishihara tests
(Note: This activity can be done by projecting the test on the screen at the front of the lab.)
Method
- Look at the four Ishihara test either on paper or projected at the front of the room.
- Note the number (if any) that you see in the circle.
Analysis
Work with your lab group to answer the following:
- The genes for the red and green receptors are on the X-chromosome. Who are most affected by a mutation to the genes for these receptors? Create a Punnett square to illustrate how this works.
- Can women be color-blind for red/green?
- Humans have three color light receptors and have trichromatic vision. Some women are described as possibly having tetrachromatic vision (seeing 4 colors) and being able to discriminate colors invisible to the rest of us. Describe a mechanism for why this could happen. Why is there a possible gender bias?
