PKU: GENETICS AND INHERITANCE, Schemes and Mind Maps of Genetics

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K a t i e G o l de n -G r a n t G e n et i c C o u n s el o r S c i e n c e N i g h t 4 / 4 / 2 014

PKU: GENETICS

AND INHERITANCE

 How genetics work

 Genetics of PKU

 Inheritance of PKU

 Genetic testing

OUTLINE

 Traits and variation between people  Hair color  Height  Skin color  Taste preferences  Ear lobe shape

EFFECTS OF GENETICS

 Impact of genetics on health

 Genetic disorders  Examples: PKU, cystic fibrosis, Down syndrome  Genetic + environmental disorders  Examples: Diabetes type II, coronary heart disease, cancer

Human  Cell  Chromosomes  DNA

HOW DO GENETICS WORK?

 Hereditary material in humans

 String of letters (base pairs) that make a code

 Code gives instructions for body to grow and develop

DNA

 Segment of DNA that produces a protein with a specific function  1 gene = 1 protein  Each protein has at least one distinct role in the body

 Humans have 20,000-25,000 genes

 2 copies of each- one from mom, one from dad

 Can be anywhere from ~300 to ~2million letters long

GENE

Gene Protein

FUNCTION

 PKU is caused by mutations in the gene PAH

 This gene codes for an enzyme (type of protein) called phenylalanine hydroxylase (PAH)  PAH breaks down phenylalanine to make tyrosine

 Severity of PKU is determined by the amount of enzyme activity - we call this “residual activity”

GENETICS OF PKU

PAH enzyme

Phenylalanine

Tyrosine

X

Phe

Phe

Phe

Phe

Phe Phe

Phe Phe

 Autosomal recessive pattern

 A person must have a mutation on BOTH of his/her two copies of the PAH gene in order to have PKU

 This only occurs if both parents are carriers for PKU

INHERITANCE OF PKU

PKU

Carrier Carrier

 All children will inherit a mutation and will be (at least) a carrier

 The chance for a child to have PKU depends on the partner

 2% (1 in 50) of the population is a carrier for PKU

 If unknown whether the partner is a carrier, the chance to have a child with PKU is 1 in 100 (1%)  Carrier testing is available for partners

 If the partner is a carrier, the chance to have a child with PKU is 1 in 2 (50%)

 If partner has PKU, all children will have PKU too

FOR A PERSON WITH PKU…

 Genetic testing can be performed to identify the two PAH gene mutations  Not done standardly, but can be for interested families  Would not tell us which one came from which parent

GENETIC TESTING

 All children born in hospitals in the USA are screened for PKU at birth

 If mutations are known…

 Carrier screening for family members can be performed  Prenatal screening for siblings can be performed