Hemophilia is a disease in which the person’s blood will not clot. The disease is inherited. If you have the dominant gene H, you will have normal blood. If you have only the recessive gene h, your blood will not clot properly. The gene is carried on the X chromosome.

Colorblindness is also a genetic disease. In this disease, the person does not see certain colors, such as red and green. This person will see green as a gray color and red as a yellow color. If you have at least one dominant gene C, you can see all colors. If you have only recessive genes, you cannot see red and green. This gene is also carried on the X chromosome.

Goals

In this exercise, you will:

a. toss coins to show children born in five families

b. see how hemophilia and colorblindness are inherited in several families

c. solve genetic problems involving hemophilia and colorblindness in some families

Keywords

• colorblindness____________________________________________________________
• hemophilia_______________________________________________________________
• sex chromosomes_________________________________________________________

Materials

Figure 1. Coins for Family 1.

            7 coins             masking tape                pen

Procedure

Part A. Hemophilia

Genes for hemophilia are located on the sex chromosomes. Remember, females have two X chromosomes (XX) while males have one X and one Y chromosome (XY). Only the X chromosomes have the genes for hemophilia. A female can be X^HX^H, X^HX^h, or X^hX^h for the clotting trait. A male can be X^HY or X^hY.

Family 1. Offspring of parents who are normal; the mother is hybrid (heterozygous).

1. Locate the coins shown in Figure 1. These coins represent the genes of the parents. The coin with a Y chromosome is the father. The coin with an X on both sides is the mother.
2. Place both coins in your cupped hands. Shake the coins and then drop them on your desktop. Do not throw coins!
3. Read the combination of letters that appears. This combination represents the result that might appear in an offspring of these parents.
4. Make a tally mark (/) in Table 1 beside the correct gene combination in the column marked “Offspring Observed.”
5. Repeat shaking and reading the coins for a total of 40 times.
6. Determine the total marks for each gene combination in Table 1 and write these totals in the proper space in the table below.

Table 1

Offspring of X^HY Father and X^HX^h Mother
Gene Combinations	Offspring observed	Total
X^HX^H
X^HX^h
X^hX^h
X^HY
X^hY

Family 2. Offspring of a father who has hemophilia and a hybrid mother.

1. Locate the two coins shown in Figure 2.
2. Place the coins in your hands and shake. Read the results and make a proper mark in Table 2.
3. Repeat step 2 for a total of 40 times. Total your marks in Table 2.

Offspring of X^hY Father and X^HX^h Mother
Gene Combinations	Offspring observed	Total
X^HX^H
X^HX^h
X^hX^h
X^HY
X^hY

Figure 2. Coins for Family 2.

Part B. Colorblindness

The genes for colorblindness are also located on the sex chromosomes. For the genes controlling colorblindness, a female can be X^BX^B, X^BX^b, or X^bX^b. A male can be either X^BY or X^bY.

Family 3. Offspring of a father who is colorblind and a mother who has two dominant genes.

1. Locate the two coins shown in Figure 3.
2. Shake the coins and read the results. Place a proper mark in Table 3.
3. Repeat step 2 for a total of 40 times. Total your marks in Table 3.

Offspring of X^bY Father and X^BX^B Mother
Gene Combinations	Offspring observed	Total
Figure 3. Coins for Family 3 X^BX^B
X^BX^b
X^bX^b
X^BY
X^bY

Family 4. Offspring of parents who are normal but the mother is hybrid.

1. Locate the two coins shown in Figure 4.
2. Shake the coins and read the results. Place a proper mark in Table 4.

Offspring of X^BY Father and X^BX^b Mother
Gene Combinations	Offspring observed	Total
X^BX^B
X^BX^b
X^bX^b
X^BY
X^bY

Figure 4. Marking coins for family 4

Part C. Problems

For each of the following problems, use the Punnett Square to the left to show your work. Record your answers in the spaces provided.

1. Two parents have the following genes for hemophilia:  X^HX^h and X^HY. What type of blood will their children have?

	Children
	Number of males	Number of females
have normal clotting
have hemophilia

2. Two parents have the following genes for colorblindness:  X^BX^B and X^bY. What kind of color vision will their children have?

	Children
	Number of males	Number of females
have normal vision
have colorblindness

3. Two parents have the following genes for colorblindness.  X^BX^b and X^bY. What type of color vision will their children have?

	Children
	Number of males	Number of females
have normal vision
have colorblindness

Questions

1. What sex chromosomes do female offspring have? ______________________________
2. What sex chromosomes do male offspring have? ________________________________
3. How many genes do females have:
1. for blood clotting? _____________
2. for colorblindness? ____________
4. How many genes do males have:
1. for blood clotting? ____________
2. for colorblindness? ___________
5. Why is there a difference in the number of genes for blood clotting and colorblindness in males and females? _______________________________________________________ _______________________________________________________________________
6. Which of the 2 traits studied in this exercise are genetic diseases? __________________ _______________________________________________________________________
7. In Problem 2, why are there no colorblind children even though one of the parents is colorblind? ______________________________________________________________
8. Which of the parents give the trait of hemophilia to their son? ______________________
9. Which of the parents give the trait of hemophilia to their daughter? _________________