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?