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Human PedigreesDrawing and Analysis
Genetic Counseling
• Helping individuals and prospective parents
• Your learning gives you the opportunity to determine some probabilities and patterns of inheritance yourself!
PedigreesA pedigree is a biological family tree
that shows the interrelationships between parents and children across generations. Helps illustrate a pattern of
inheritance for a single trait through that family
Standard Symbols in Pedigrees
Male Unspecified Gender
Female
Standard Symbols in Pedigrees
Clinically Unaffected
Clinically Affected
Carrier
Not Clinically Affected
Some pedigrees show phenotype only (no half-shaded boxes; some show genotype (carriers are half-shaded) You will need to determine which system is used in each problem.
Conventions in Drawing Pedigrees
Male partner on left (usually)
Parents
Regardless of Social Relationship
Conventions in Drawing Pedigrees
Full Siblings
(in order of age from left to right)
I
II
1 2
1 2 3
Conventions in Drawing Pedigrees
Dizygotic Twins Monozygotic Twins
I
II
1 2
1 2 3 4
Conventions in Drawing Pedigrees
Adopted
Consanguinity
Separated
I
II
1 2 3
1 2 3
Conventions summary
Patterns of Inheritance• Dominant:
– Trait is expressed in every generation – eg. Huntington’s, brown eyes
– Not seen in offspring unless present in a parent• Recessive:
– Trait may skip generations – eg. TaySachs• Sex-Linked:
– Y linked – only males are clinically affected– X linked – affected males more common, may
have normal parents, affected females must have affected father
autosomal dominant
Pedigree Practice
A) Autosomal dominant
B) Autosomal recessive
C) X-linked recessive
Pedigree Practice (more rare)
D) X-linked dominant
E) Y-linked
Pedigree Practice
Cardiomyopathy (hypertrophy)
Autosomal dominant
Pedigree Practice
Warped ear
Autosomal recessive
Pedigree Practice
Neurofibromatosis
Autosomal dominant
Pedigree practice
Hemophilia
X-linked recessive