Polydactyly

Brachydactyly

Human Pedigree Analysis

A child that has retinoblastoma

Manute Bol had Marfan Sydrome

Michael Phelps has Marfan Sydrome

Human Pedigree Analysis

Anatomy of a Pedigree

Male (left) Female (right)

Affected individuals

Carriers (Heterozygotes for autosomal recessive)

Deceased individuals

Sex unspecified

Anatomy of a Pedigree

Generation

Mating

Adoption

Siblings

Identical twins

Fraternal twins

Consanguineous marriage

Autosomal dominant (e.g., retinoblastoma)

AAaffected

Aaaffected

Aaaffected

aaunaffected

A a

A

a

Affected parent (Aa) X Affected parent (Aa)

Autosomal recessive (e.g., PKU)

Aaunaffected

(carrier)No PKU

aaaffected

PKU

Aaunaffected

(carrier)No PKU

aaaffected

PKU

A a

a

a

Unaffected parent (Aa) X Affected parent (aa)

Autosomal Dominant (e.g., Huntington disease)

Characteristics of a Dominant Pedigree

• An affected individual has at least one affected parent

• As a result, dominant traits show a vertical pattern of inheritance – the trait shows up every generation

• Two affected individuals may have unaffected children

AA AaAa aa

A a

a

a

A

Autosomal Recessive (e.g., cystic fibrosis)

Characteristics of Recessive Pedigrees

• In pedigrees involving rare traits, a horizontal pattern of inheritance is observed– the trait may not appear in every generation

• An individual who is affected may have parents who are not affected, particularly as a result of consagineous matings

• All the children of two affected individuals are affected

aa aaaa aa

a a

a

a

Pedigree of a family with some members showing the Marfan Syndrome

Marfan syndrome is

Marfan syndrome is

Issues with genetic screening

• Why carry out genetic screening at all?• When is a test accurate and comprehensive enough to be

used as the basis for screening?• Once an accurate test becomes available at reasonable

cost, should screening become required or optional?• If a screening program is established, who should be

tested?• Should private companies and insurance companies have

access to employees and client test results?• What education needs to be provided regarding test

results?