Title: How Are Traits on Sex Chromosomes Inherited?
Name _______________________
Period _____
Introduction:
Genes for blood clotting and color vision are located on the sex chromosomes,
specifically the X chromosome. Remember, females have two X chromosomes (XX)
while males have one X and one Y (XY).
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 normally.
Color blindness is a genetic condition in which a person does not see certain
colors, such as green and red. This person will see green as a gray color and red as a
yellow color. If you have at least one dominant gene "B", you can see all colors. If you
have only recessive genes "b", you cannot see green and red.
In this lab you will
a. toss coins to show children born in four families.
b. see how hemophilia and color blindness are inherited in several families.
c. solve genetic problems involving hemophilia and color blindness.
MATERIALS:
envelope with 3 labeled coins
plastic bag with four labeled coins
PROCEDURE:
Part A- Hemophilia
A female can be XHXH, XHXh, or XhXh for blood clotting.
A male can be XHY, or XhY.
Family 1.
Offspring of parents who are normal, the mother is a carrier for hemophilia.
1. Find the following coins in your envelope.
Coin 1
XH
Y
Male
XH
Coin 2
Female
Xh
These coins represent the genes of the parents. The coin with the Y chromosome is the
father and the coin with an X on each side is the mother.
2. Place both coins in cupped hands. Shake the coins and then drop them on
on the your desktop.
3. Read the combination of letters that appears. This combination represents the
genotype observed in an offspring of these parents.
1
4. In Table 1 below, make a tallymark (/) beside the correct genotype in the row
marked "Offspring Observed".
5. Repeat shaking and reading the coins for a total of 20 times.
6. Total all offspring observed in the "Total" column.
7. For each genotype, calculate the number of expected offspring out of 20 offspring.
Use the expected number of each from your Punnett square on page 1. Record this
number in the row labeled “Expected Offspring Number”. If you have observed
offspring of a genotype not shown in Table 1 you may have used the wrong coins to
collect your data.
Table 1: Offspring of XHY Father and XHXh Mother
Gene Combinations
XHXH
XHXh
XHY
XhY
Observed Offspring
= 20
Observed Totals
= 20
Expected Offspring
Number
Family 2:
Offspring of a father who has hemophilia and a mother who is a carrier for
hemophilia.
1. Find the following coins in your envelope.
Coin 1
h
X
Y
Male
XH
Coin 2
Female
Xh
These coins represent the genes of the parents. The coin with the Y chromosome is the
father and the coin with an X on each side is the mother.
2. Place both coins in cupped hands. Shake the coins and then drop them on
on the your desktop.
3. Read the combination of letters that appears. This combination represents the
genotype observed in an offspring of these parents.
4. In Table 2 below, make a tallymark (/) beside the correct genotype in the row
marked "Offspring Observed".
5. Repeat shaking and reading the coins for a total of 20 times.
6. Total all offspring observed in the "Total" column.
2
7. For each genotype, calculate the number of expected offspring out of 20 offspring.
Use the expected number of each from your Punnett square on page 1. Record this
number in the row labeled “Expected Offspring Number”. If you have observed
offspring of a genotype not shown in Table 1 you may have used the wrong coins to
collect your data.
Table 2: Offspring of XhY Father and XHXh Mother
Gene Combinations
XHXH
XHXh
X hX h
XHY
Xh Y
Observed Offspring
= 20
Observed Totals
= 20
Expected Offspring
Number
PART B- Color Blindness
A female can be XBXB, XBXb, or XbXb for the color vision gene.
A male can be XBY or XbY for the color vision gene.
Family 3.
Offspring of a father who is color blind and a mother who is homozygous
dominant.
1. Find the following coins in your plastic bag.
Coin 1
b
X
Y
Male
XB
Coin 2
Female
XB
These coins represent the genes of the parents. The coin with the Y chromosome is the
father and the coin with an X on each side is the mother.
2. Place both coins in cupped hands. Shake the coins and then drop them on
on the your desktop.
3. Read the combination of letters that appears. This combination represents the
genotype observed in an offspring of these parents.
4. In Table 2 below, make a tallymark (/) beside the correct genotype in the row
marked "Offspring Observed".
5. Repeat shaking and reading the coins for a total of 20 times.
6. Total all offspring observed in the "Total" column.
3
7. For each genotype, calculate the number of expected offspring out of 20 offspring.
Use the expected number of each from your Punnett square on page 1. Record this
number in the row labeled “Expected Offspring Number”. If you have observed
offspring of a genotype not shown in Table 1 you may have used the wrong coins to
collect your data.
Table 3: Offspring of XbY Father and XBXB Mother
Gene Combinations
XBXB
XBXb
XbXb
XBY
X bY
Observed Offspring
= 20
Observed Totals
= 20
Expected Offspring
Number
Family 4.
Offspring of parents who are normal but the mother is heterozygous.
1. Find the following coins in your plastic bag.
Coin 1
B
X
Y
Male
XB
Coin 2
Female
Xb
These coins represent the genes of the parents. The coin with the Y chromosome is the
father and the coin with an X on each side is the mother.
2. Place both coins in cupped hands. Shake the coins and then drop them on
on the your desktop.
3. Read the combination of letters that appears. This combination represents the
genotype observed in an offspring of these parents.
4. In Table 2 below, make a tallymark (/) beside the correct genotype in the row
marked "Offspring Observed".
5. Repeat shaking and reading the coins for a total of 20 times.
6. Total all offspring observed in the "Total" column.
7. For each genotype, calculate the number of expected offspring out of 20 offspring.
Use the expected number of each from your Punnett square on page 1. Record this
number in the row labeled “Expected Offspring Number”. If you have observed
offspring of a genotype not shown in Table 1 you may have used the wrong coins to
collect your data.
4
Table 4: Offspring of XBY Father and XBXb Mother
Gene Combinations
XBXB
XBXb
XbXb
XBY
X bY
Observed Offspring
= 20
Observed Totals
= 20
Expected Offspring
Number
Part C- Problems
For each of the following problems complete a Punnett Square then record your
answers in the spaces provided.
1. A mother who is heterozygous for blood clotting and a father who is normal for blood
clotting want to know what their children could be like for blood clotting.
Children
Number of Number of
Males
Females
Have
Normal Blood
_______
_________
Have
Hemophilia
_______
_________
2. A mother who is homozygous dominant for color vision and a father who is color
blind want to know what their children could be like for color vision.
Children
Number of Number of
Males
Females
Have
Normal Color Vision
_______
_________
Have
Color Blindness
_______
_________
3. A mother who is heterozygous for color vision and a father who is color blind want to
know what their children could be like for color vision.
Children
Number of Number of
Males
Females
Have
Normal Color Vision
_______
_________
Have
Color Blindness
_______
_________
5
Discussion Questions:
1. What are the sex chromosomes of females? ___________
2. What are the sex chromosomes of males? ___________
3. On which chromosome, the X or the Y, is the gene for color vision located? __________
4. How many genes do females have for color vision? ___________
5. How many genes do males have for color vision? ___________
6. On which chromosome, the X or the Y, is the gene for blood clotting located? _______
7. How many genes do females have for blood clotting? ___________
8. How many genes do males have for blood clotting? ___________
9. Why is there a difference in the number of genes for color vision and blood clotting in
males and females? ______________________________________________________________
10. In Part C, Problem 2, why are there no color blind children even though one of the
parents is color blind? ____________________________________________________________
_________________________________________________________________________________
11. From whom does a son inherit the trait of hemophilia? _____________________________
12. From whom does a daughter inherit the trait of hemophilia? _______________________
6