Pedigrees: How to make and interpret pedigree charts
What are pedigrees used for?
Symbols used on a pedigree chart:
Male
Female
Parents of a child
Siblings
Twins –
Fraternal
Identical
Practice: draw your family pedigree chart back 3 generations (you, your parents, your
grandparents)
The following symbols are used when analyzing for a genetic disease/disorder
Affected
X-linked carrier
Autosomal carrier
Deceased
X-linked vs. autosomal genetic disorders/diseases
X-linked diseases lie on the ____ chromosome
Autosomal diseases lie on any of the other chromosomes (chromosomes # ______)
HOW DO YOU TELL?
If a disease/disorder is X-linked, then significantly more ___________ will be affected by the
disease.
If a disease/disorder is autosomal, then females/males will be nearly equally affected.
Power point example A: Is the disease X-linked or autosomal? _____________
Explain your answer:
Dominant vs. Recessive genetic disorders/diseases
Dominant diseases need _______________ disease allele to be expressed
Recessive diseases must have __________ of the disease allele to be expressed
HOW DO YOU TELL?
If a disease/disorder is dominant, then at least one parent of each affected person must also
express it
If a disease/disorder is recessive, it can ‘skip a generation’ because both parents were
_____________________
Power point example B: Is the example dominant or recessive?______________
Explain your answer:
Power point example C: Is the example dominant or recessive?______________
Explain your answer:
Practice questions
1 a) Is the following autosomal or X-linked? _______________________
b) Is it dominant or recessive? ________________________
c) Explain your answer
2 a) Is the following autosomal or X-linked? _______________________
b) Is it dominant or recessive? ________________________
c) Explain your answer
APPLICATION: Analyzing the types of muscular dystrophy
The term muscular dystrophy (MD) refers to a group of genetic diseases marked by progressive
weakness and degeneration of the skeletal, or voluntary, muscles, which control movement. The
muscles of the heart and some other involuntary muscles are also affected in some forms of
muscular dystrophy, and a few forms involve other organs as well. There are currently 9
defined forms of muscular dystrophy, based on the location of the affected muscles.
Walking with muscular dystrophy is described as _________________________
Once attributed to malnutrition, it is now known that muscular dystrophy is an inherited disease
marked by improperly formed proteins which play a role in supporting the structure of muscle
fiber. Each form of MD also follows a different inheritance pattern.
Your goal is to determine, using a pedigree chart, which inheritance pattern the following
examples of muscular dystrophy follow (i.e. are they autosomal or X-linked? are they dominant
or recessive?)
Complete these application questions IN YOUR JOURNAL
For each question below,
a) draw the pedigree
b) determine whether the inheritance pattern is X linked or autosomal
c) determine whether the inheritance pattern is dominant or recessive
d) Final step (only if recessive) fill in each unaffected person with appropriate symbol if you
know they are a carrier. If you cannot determine their carrier status, fill in with a ‘?’
3. Chad and Veronica got married and had Brittany, Kristin, and Harry. It was discovered that
Harry had muscular dystrophy. Brittany married Larry and had son Stephan and daughter
Stephanie. Stephan also had muscular dystrophy. Larry’s brother Barry also had muscular
dystrophy but neither of their parents had the disorder.
4. Lisa and Ashton got married and had three girls, Carrie, Mary, and Teri. It was discovered
that Lisa had muscular dystrophy. Teri married Perry and had two boys, Pike and Tike. It was
discovered that Teri and Pike had muscular dystrophy.
5. Debbie married David and had three children: Darren, Dawn, and Derek. David, Darren and
Derek discovered they have muscular dystrophy. Derek married Didi and had two daughters,
Denise and Destiny. Denise also has muscular dystrophy and married Dirk. They had a girl, Dee,
and a boy, Deven. Dee has muscular dystrophy.