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