Name:
Date:
HUMAN PEDIGREE WS
Standards: Genetics 2e, 2f, 2g, 3a, and 3c
Objectives:
 Students should be able to interpret a human pedigree.
 Students shall be able trace x-linked traits through a pedigree.
A sex-linked characteristic is determined by an allele that is
carried only on the X chromosome. The shorter Y chromosome
does not carry an allele for a sex-linked trait. Most sex-linked
traits are recessive. Since there is only one X in his genotype,
XY, a male who carries a particular recessive allele on the X
chromosome will have the sex-linked condition. A female who carries a
recessive allele in one X chromosome will not show the condition if there is a
dominant allele on her other X chromosome. She will express the recessive
condition only if she inherits two recessive alleles—one from each parent. Her
chances of inheriting the condition are far less compared with males.
One sex-linked trait is hemophilia, a condition in which the blood does
not clot properly. Common injuries and bruises can be fatal to a person who
suffers from hemophilia. Since men possess only one X chromosome (XY), they
are more likely to inherit the disease than women.
1. What is a sex-linked trait? A sex-linked characteristic is determined by an
allele that is carried only on the X chromosome
2. Can women and men both inherit SEX-LINKED TRAITS (yes or no)?
3. Who is more likely to inherit a sex-linked trait, Men or Women (circle)?
Explain?
Since men possess only one X chromosome (XY), they are more
likely to inherit the disease than women.
HUMAN PEDIGREE
(Expressing Hemophilia)
Per.:
I
4. Study the pedigree and answer the following question (# 5-10).
5. Squares represent males . If the square is darkened, he has hemophilia
(genotype= XhY ); if clear he has normal blood clotting (genotype= XHY ).
6
a. How many males have hemophilia?
5
b. How many males do not have hemophilia?
6. Circles represent females. If it is completely darkened, she has hemophilia
(genotype= XhXh ); if clear she is normal for blood clotting (genotype= XHXH
).
2
a. How many females have hemophilia?
3
b. How many females are pure-bred dominant for normal blood
clotting?
7. Some circles are half shaded for females. Half shaded circles represent a
heterozygous condition for hemophilia where her genotype expresses one
dominant and one recessive trait (i.e.= XHXh). Females who are heterozygous
are called “carriers.” The females are normal, however they can pass the
recessive trait to their children.
8
a. How many females are “carriers” for hemophilia?
8. A marriage is indicated by a horizontal line connecting a circle to a square.
6
a. How many marriages are present?
9. Each generation is represented along with the offspring associated with each.
4
a. How many generations are present in this pedigree?
10. A line perpendicular to a marriage line indicates the offspring. The first
child is represented on the left and the last child is to the right.
5
a. How many children did the first generation have?
Name:
Date:
HUMAN PEDIGREE WS
Per.:
I
Applying the skill: Translate the following symbols into a genotype
and phenotype, and assess the health status of individuals with sexlinked traits.
Symbol
Genotype
Analysis: Use the pedigree above to answer questions #11-13
11. Why did family members in the second generation experience some
14.
form of hemophilia?
XhY
Both parents carried an affected x chromosome.
The father would give Xh () to his daughters and a Y to his sons ().
The mother had a 50% chance of giving Xh () or XH () to her
children.
12.
2
Phenotype
Hemophilia,
Normal, or
Carrier.
Affected  or
NOT Affected

Hemophilia

Normal

Carrier

Normal

Hemophilia

15.
XHXH
16.
a. How many children did couple 3-4 have?
b. Why did child #11 receive a recessive hemophilia trait and #13 did not?
XHXh
17.
Child #11: Her father’s genotype is XhY (). All X’s are recessive and since
she is a girl that is the only Xh.
XHY
18.
Child#13: Despite the father having hemophilia, ALL sons will avoid the
disease. ALL sons will receive a Y from dad ().
13. Child #13 did not have hemophilia and the family history with hemophilia
could have ended with him. Why did his children end up with hemophilia?
Child #13 fell in love with a woman with hemophilia (XhXh). A very-very
unlikely scenario and he should have seen the symptoms ahead of time.
XhXh