Download How are traits inherited lab

How are Traits on Sex Chromosomes Inherited?
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.
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.
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
8 pennies, 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 XHXH, XHXh, or XhXh for the clotting trait.
A male can be XHY or XhY.
Figure 1. Marking coins for
family 1.
XH
front
XH
front
Y
Coin 1
Male
back
Xh
Coin 2
Female
back
Family 1 - Offspring of parents who are normal; the mother is
hybrid (heterozygous).
Offspring of XHY Father and XHXh Mother
1. Place the tape on both sides of two coins.
Gene
Offspring
Total
2. Mark the coins as shown in Figure 1. These coins
Combinations
observed
represent the genes of the parents. The coin with the
H H
X
X
Y chromosome is the father. The coin with an X on
each side is the mother.
XHXh
3. Place both coins in your cupped hands. Shake the
XhXh
coins and then drop them on your desktop.
XHY
4. Read the combination of letters that appears. This
XhY
combination represents the result that might appear
in an offspring of these parents.
Table 1
5. Make a mark (/) in Table 1 beside the correct gene combination in the column marked “Offspring
Observed.”
6. Repeat shaking and reading the coins for a total of 40 times.
7. Determine the total marks for each gene combination in Table 1 and write these totals in the proper
space in the table.
Part B: Colorblindness
The genes for colorblindness are also located on the sex chromosomes. For the genes controlling
colorblindness, a female can be XBXB, XBXb, or XbXb. A male can be either XBY or XbY.
Family 2 - Offspring of a father who is colorblind and a mother who has two dominant genes.
1. Place tape on two coins and mark them as shown in Figure 2.
2. Shake the coins and read the results. Place a proper mark in Table 2.
3. Repeat step 2 for a total of 40 times. Total your marks in Table 2.
Figure 2. Marking coins for family 2
Xb
front
XB
front
Coin 5
Male
Y
back
Coin 6
Female
XB
back
Offspring of XbY Father and XBXB Mother
Gene
Offspring
Total
Combinations
observed
XBXB
XBXb
XbXb
XBY
XbY
Part C: Problems
For each of the following problems, construct and use a Punnett Square. Record your answers in the spaces
provided.
1. Two parents have the following genes for hemophilia: XHXh and XHY. 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: XBXB and XbY. 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. XBXb and XbY. What type of color
vision will their children have?
Children
Number of males
Number of females
have normal vision
have colorblindness
Analysis Questions:
1. What sex chromosomes do female offspring have? ______________________________
2. What sex chromosomes do male offspring have? ________________________________
3. How many genes do females have:
a. for blood clotting? _____________
b. for colorblindness? ____________
4. How many genes do males have:
a. for blood clotting? ____________
b. 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 Family 1, why is there a child with hemophilia even though neither parent has hemophilia?
______________________________________________________________
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? _________________