How is colorblindness transmitted?
LAB HANDOUT # _____
Background:
Three human genes associated with color vision are located on the X chromosome. In males a
defective version of any one of these gene produces colorblindness. Colorblindness is found in about
1 in 10 males in the United States. Among females however, colorblindness is only found in about 1 in
100 females. In this lab you will simulate how colorblindness is transmitted by using beans and cups.
The white beans in the lab represent X chromosomes and the red bean represents the Y chromosome.
The black circle on a bean represents the gene for colorblindness.
What you need:
1 cup labeled mother with 2 beans (1 white bean with black circle and 1 plain white bean)
1 cup labeled father with 2 beans (1 white bean with black circle and 1 red bean)
Procedure:
1. Without looking draw one bean out from the mother cup and one bean out from the father
cup.
2. Record bean colors on the data table.
3. Based on the colors of the beans indicate the sex and vision of the offspring.
4. Put the beans back and repeat steps 1-3 for a total of 10 trials.
Key:
1 plain white bean + 1 red bean = Male, normal vision
1 white bean with black circle + 1 red bean = Male, colorblind
1 plain white bean+ 1 white bean with black circle= Female, normal vision
2 white beans with black circles = Female, colorblind
RED
Name___________________________________________________________Date______________Period_____
Lab: How is colorblindness transmitted?
Background: Colorblindness is is the decreased ability to perceive
differences between some of the colors that others can distinguish. There
are many forms of colorblindness but one of the major types is individuals
who have difficultly distinguishing between red and green. Look at the
colorblind test at your table and write the number or word you see in the
picture below.
Picture 1. _______________________
Picture 2. _______________________
Picture 3. _______________________
Picture 4. _________________________
Picture 5. _________________________
Picture 6. _________________________
Look at the pedigree chart below for colorblindness. Use the key and the pedigree to answer the
questions that follow.
1. What does the square represent? ____________________
2. What does the circle represent? ______________________
3. What does the color white represent? ______________________________
4. What does the color black represent? ______________________________
5. In order to be male, which chromosome must you receive? ________
6. Who can give you a Y chromosome? ________________
7. If colorblindness were linked to the Y chromosome then all (MALE OR
FEMALE) offspring would be
colorblind.
8. Look at the pedigree chart. The first male is colorblind. Are his sons colorblind as well? YES OR NO
9. Because none of the sons of a colorblind father are colorblind, we now know that colorblindness is
linked to which chromosome?
X
OR
Y
10. If N stands for normal vision. What would be the genotype of the carrier female? ___________
11. Why are all the daughters of a colorblind male either colorblind or carriers?
___________________________________________________________________________________________________
__________________________________________________________________________________________________
Carefully read the lab handout to fill in the chart below.
How is colorblindness transmitted?
Trial
Bean colors
Male or female?
Example
Red
White with black circle
Male
Normal vision or
colorblind?
colorblind
1
2
3
4
5
6
7
8
9
10
Use your chart and the lab handout to answer the following questions.
12. What did the white bean represent? _________________
red bean?____________________
13. What did the black circle represent? __________________________________________________
14. How many males where there? __________________ females? _______________
15. How many were colorblind? _____________________ normal vision? ______________
16. How many females were colorblind? ____________ males? _________________
17. Which sex had more trials of being colorblind?
MALE
OR
FEMALE
18. After completing this activity, which sex do you think is more likely to inherit a recessive x-linked
trait for colorblindness?
MALE
OR
FEMALE
Polygenetic Traits – Some traits, like height or skin color, are controlled by two or more genes. These
traits often work like light switches- The more genes are “on,” the taller or darker you are, the more
genes are “off,” the shorter or lighter you are. Flip a coin for each gene- Heads is “on” and tails if “off.”
Gene
On or Off
1
2
8 on/ 0 off
7 on/ 1 off
6 on/ 2 off
7 ft. tall
6 ft. 9 in.
6 ft. 6 in.
3
4
5
6
7
8
5 on/ 3 off
4 on/ 4 off
3 on/ 5 off
2 on/ 6 off
1 on/ 7 off 0 on/ 8 off
6 ft.
5 ft. 9 in.
5 ft. 6 in.
5 ft. 3 in.
5 ft.
How tall were you? __________________
4 ft. 9 in.