INTERPRETING INFORMATION IN A PEDIGREE
Name ___________________
Date _________ Period _____
Organizing information is often the key to solving a problem. Tracing the
hereditary characteristics over many generations can be especially
confusing unless the information is well organized. In this activity, you
will learn how to organize hereditary information, making it much easier to
analyze.
In this activity you will construct and analyze a pedigree.
1. Pedigree 1 traces the dimples trait through three generations of a
family. Blackened symbols
represent people with dimples. Dimples are
inherited as a dominant trait. Circles represent
females and
square represent males.
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II
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Pedigree 1
2. The following passage describes the family shown in Pedigree 1.
Although Jane and Joe Smith have dimples, their daughter, Clarissa does
not. Joe’s dad has
dimples, but his mother, and his sister,
Grace do not. Jane’s dad, Mr. Renaldo, her brother,
Jorge, and her
sister, Emily, do not have dimples, but her mother does.
3. Write the name of each person below the correct symbol in Pedigree 1.
How are marriage
and offspring symbolized?
______________________________________________
What do the Roman numerals symbolize?
___________________________________
4. Make a pedigree based on the following passage about freckles.
Freckles are inherited as a
dominant trait. Write the name and
genotype of each individual under the appropriate
symbol.
Remember to include all of the parts of a pedigree.
Andy, Penny, and Delbert have freckles, but their mother, Mrs. Cummins,
does not. Mrs.
Giordano, Mrs. Cummins sister, has freckles like
her father, Mr. Lutz, but her mother, Mrs.
Lutz does not have
freckles. Deidra and Darlene Giordano are freckled, but their sister,
Dixie, like her father, is not freckled.
5. What advantages does a pedigree have over a written passage?
_____________________
________________________________________________________________
6. How does a pedigree organize hereditary information, making it easier
to understand?
_____________________________________________________________________
A HUMAN
PEDIGREE
Name ________________________
Date ___________ Period
________
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 X-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 on 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 thus greatly reduced.
One sex-linked trait is hemophilia, a condition in which the blood does not
clot properly. Most people who have hemophilia are men. In this
investigation, you will determine why this is occurs.
Procedure:
1. Study the pedigree for hemophilia shown in Figure A. In a pedigree, a
square represents a
male. If it is darkened, he has hemophilia;
if clear, he has normal blood clotting.
How many males represented by this pedigree have hemophilia? How many
males are normal?
# if males with hemophilia: __________
# of normal males:
__________
2. A circle represents a female.
if clear, she is normal.
If it is darkened, she has hemophilia;
How many females in this pedigree have hemophilia? How many are
normal?
# if females with hemophilia: __________
# of normal females:
__________
3. A marriage is indicated by a horizontal line connecting a circle to a
square.
How many marriages are indicated in the pedigree?
__________
4. A line perpendicular to a marriage line indicates the offspring. If
the line ends with either a
circle or square, the couple had only one
child. However, if the line is connected to another
horizontal
line, then several children were produced, each indicated by a short
vertical line
connected to the horizontal line. The oldest child
appears to the left and the youngest child
to the right.
How many children did the first couple have?
5. II represents the second generation.
generation, and so on.
__________
III represents the third
How many generations are represented in this pedigree?
__________
Figure A
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Pedigree of Heredity
6. The genotypes of the males in a pedigree for sex-linked inheritance are
easy to determine
since normal blood clotting (XN) is dominant and
hemophilia (Xn) is recessive. Since these
alleles are on the X
chromosome only, a male represented by a clear square will have the
genotype XNY. One represented by a darkened square will be XnY. Label
the genotypes of
all the squares.
How many males have the genotype XNY?
_________________
7. Females who have hemophilia have an easy genotype to identify. They
are all XnXn. Both
recessive alleles must be present for a
female to have hemophilia. If one dominant allele is
present (XN)
the individual would be normal for clotting. Label all the females with
hemophilia as genotype XnXn on the pedigree.
How many women have genotype XnXn in this pedigree?
_________________
8. Females who do not show the trait for hemophilia may be homozygous
dominant (XNXN) or
heterozygous (XNXn). A heterozygous female is
called a carrier. Examination of offspring
can often determine which
genotype the parents have. If any child (son or daughter) has
hemophilia, then the female must be heterozygous (XNXn). If her son
has hemophilia, he has
genotype XnY. He inherited the Y from the father,
so the other allele in his genotype (Xn)
had to come from the
n
n
mother. If a daughter has hemophilia (X X ), she inherited an Xn
from each parent, thus making the genotype of the normal mother XnXn.
Label all female
XNXn that have children with hemophilia.
What is the genotype of the female in the first generation?
_____________
9. Females who have more than four sons, with none exhibiting hemophilia,
are likely to be
genotype XNXN. If she has had four or fewer sons,
her genotype is less certain. In such
cases her genotype is labeled
N
?
as X X . Label the rest of the females in the pedigree as
XNX? or
XNXN.
How many females in the pedigree have the genotype XNXN?
__________
10. The genotype of all people represented in the pedigree should now be
labeled.
Complete the following chart using the pedigree in figure B.
Figure B
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11. Label the genotypes of the individuals in the pedigree of Figure B.
Table B Pedigree Analysis
12. Fill in Table B based on the pedigree in Figure B.
Questions about the pedigree in Figure B
Number of generations
Number of men with hemophilia
Number of women with normal blood clotting
Number of marriages
Number of men with genotype XNY
Number of women with genotype XnXn
Number of single women
Number of people that never married
Number of women with genotype XNX?
Number of couples with only one child
Answer
Analysis and Conclusions
1. Which sex usually inherits a sex-linked condition? Explain why.
___________________
___________________________________________________________________________
___________________________________________________________
2. How can you tell whether a female has a genotype XNXN, XNXn, or XNX??
___________________________________________________________________________
___________________________________________________________
3. How many genotypes are possible in a pedigree of sex-linked traits?
_____ What are they?
___________________________________________________________________________
___________________________________________________________