Family Pedigree Lab Report
Introduction:
What family were you studying?
What were the traits you studied in this family?
What is a pedigree?
What is a punnett square?
Procedure:
How did you set up the pedigree?
What are the symbols on a pedigree?
What do the symbols stand for?
How did you organize and label the generations?
What can a pedigree tell you?
Analysis and Data:
Include your completed pedigree and 8 punnett
squares.
Conclusion:
Explain how you figured out the genotype of all
the family members.
What is a dominant trait and what is a recessive
trait?
How can a punnett square be used to predict the
possible offspring?
What is a sex-linked trait?
What information did you find out about the
Flibnob family?
Pedigree and Analysis
1. Construct a pedigree of your family or the family of a friend for a single inherited trait. It can be a normal
human variation (e.g., attached ear lobes, mid digital hair, tongue curling, bent little finger, dimples, cleft
chin, widow's peak, big toe or index finger length) or a disorder. Use standard pedigree notations and
symbols and provide a legend to explain the symbols used. Put an arrow pointing to the proband (you, if you
are in the pedigree). Generations and individuals should be appropriately labeled so they can be referred to
in your analysis. If you do not know a person's phenotype you must use a "?" in their box or circle, because
a blank symbol means they definitely do not have the trait studied. If a person does not have children use the
appropriate symbol. If the trait is not usually present at birth and has a later age of onset, you must indicate
the ages on the pedigree of those not affected. Spouses, if not relevant, may be left out. The pedigree is best
drawn by hand but if you prefer, you may use your computer.
2. Describe the trait in some detail, drawings or illustrations may be useful. Define what "affected" and
"unaffected" means in your pedigree. Indicate genotype when appropriate. Remember that a person with a
dominant trait may have to be "D_" unless you are certain of the second allele. Discuss age of onset, any
evidence of variable expressivity and/or incomplete penetrance (not all traits show these variations). Go to
OMIM or other recent sources for descriptions of the trait and to find out what patterns of inheritance have
been found in families with the same trait. The OMIM search page explains how to reference OMIM
articles.
3. Analyze your pedigree by going through each mode of inheritance (AD, AR, XD, XR, and Y) explaining
how your pedigree is consistent or not consistent with each. For those you cannot rule out, explain which is
the most probable. If the mode of inheritance is known, explain how your pedigree is consistent with the
known mode of inheritance. Be sure to refer to individuals in your pedigree by generation and number, e.g.
III-1 when using them as examples of how to rule out a particular pattern of inheritance.
Explain how your pedigree is or is not consistent with the various pattern(s). Go through each pattern of
inheritance (AD, XD, CD, AR, XR, Y, multifactorial and mitochondrial) and explain how you can or cannot
rule out each pattern. Either start or end your analysis with what pattern of inheritance best explains your
pedigree and why. If the mode of inheritance is known, you should then show how your family pedigree is
consistent with the known mode.
Remember that one does not find every possible feature of any one pattern in one pedigree. For example, an
AD disorder will not always result in 50% of the children of an affected person being affected. Nor can you
rule out AR because the trait appears in every generation or because there is no consanguinity. A common
AR trait can show a vertical pattern. When analyzing pedigrees, it is best to identify AD by the fact that
those affected have an affected parent, that both males and females are affected and both can pass the gene
on to their offspring. But even an AD can be sex limited and, therefore, non penetrant in one sex so be
careful.
Grading criteria for the pedigree analysis are
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Is the paper organized well? Is the paragraphing done properly? Does each paragraph have a topic
sentence followed by supporting data and a closing? Are there headings and are they meaningful? Is
there redundancy?
Is the trait clearly described? Is the age of onset clearly stated? Is there variable expressivity and/or
incomplete penetrance?
Is there a clear and accurate legend?
Are the symbols used correctly? Are unknown phenotypes indicated?
Are the generations and individuals labeled correctly and referred to correctly in the accompanying
analysis?
Is the inheritance pattern known? If so, does your family fit? Explain. If it is not known, what is the
most likely pattern of inheritance and why? State your reasons for choosing the pattern, support the
choice logically and correctly. If available, point out matings where both are "affected" and/or both
are "not affected" to support your choice
Are all other patterns of inheritance discussed and ruled in or out using sound arguments?
Are the literature sources correctly identified and cited (using standard journal or OMIM format)?
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Do you show a clear understanding of how to analyze the pedigree of a single (large or multi
generational) family to confirm or suggest the mode of inheritance?
Approximate distribution of assigned points on pedigree assignment:
(10) Explanation/description of the trait along with known mode of inheritance or most probable
mode
(10) Title, pedigree drawn accurately (indicating known and unknown phenotypes) with a clear and
appropriate legend
(10) Analysis of the pedigree with a discussion of possible mode(s) of inheritance using specific
individuals to illustrate.