Other Types of Inheritance Epistasis – one gene affects the expression of another gene – Example: albinism – gene for color and a gene for how MUCH color Pleiotropy – a single gene affects multiple traits – Example: Phenylketonuria – gene coding for a single enzyme is responsible for multiple effects (mental retardation, inability to metabolize phenylalanine, reduced pigmentation, etc) Polygenic Inheritance – more than one gene determines the trait – Lots of diseases are polygenic b/c more than one gene plays a role in the disease (cancer, heart disease, etc)

Genetic Disorders What to know? – Whether it’s dominant or recessive – Whether it’s autosomal or sex-linked – If it results from a chromosomal mutation (like nondisjunction) – What the characteristics of the disease are

Genetic Disorders PKU Cystic Fibrosis Sickle-cell anemia Tay-Sachs Huntington’s Red-green color blindness Hemophilia Duchenne Muscular Dystrophy Down Syndrome Turner Syndrome Klinefelter Syndrome Cri du chat syndrome

PKU (phenylketonuria) Autosomal recessive Don’t produce enzyme phenylalanine hydroxylase Mental retardation, reduced pigmentation, inability to break down phenylalanine

Cystic Fibrosis Autosomal recessive Mutation in enzyme that affects fluid in lungs Build-up of thick, sticky mucous in lungs  increased infection Lifespan better now than in the past (people live into their 40s or even 50s) More common in caucasian

Sickle-cell anemia Autosomal recessive codominance = heterozygous express some sickling which makes them resistant to malaria More common in African Americans

Tay-Sachs Autosomal recessive Lack an enzyme that breaks down product in nervous system  disease of nervous system Deafness, blindness, lack of muscle control and function… Usually death by 3 – 5 yrs

Huntington’s Disease Autosomal dominant Degradation of neurons  decreased mental and motor functions (dementia, seizures, etc) Usually onset occurs around 35 – 45 yrs old

Red-green color blindness Sex-linked recessive Defect in retinal cones that detect/transmit info about color to brain Much more common in males than females If father is colorblind, daughter is carrier

Hemophilia Sex-linked recessive Lack of or defective clotting factors that allow blood to coagulate and stop bleeding Much more common in males than females If father has it, daughter is a carrier

Duchenne Muscular Dystrophy Sex-linked recessive Defective gene for dystrophin, a protein in muscles Mental retardation, muscle weakness, symptoms worsen rapidly More common in males If father has it, daughter is a carrier

Down Syndrome Trisomy 21 (results from nondisjunction of chromosome 21 in meiosis) Mental and physical impairment (wide range) Diagnose with KARYOTYPE

Turner Syndrome Monosomy of X (results from nondisjunction during meiosis) Lack full female development; sterile, shorter, stocky, short neck, webbed neck Diagnose with KARYOTYPE

Klinefelter Syndrome Male with extra X chromosome (XXY) (nondisjunction during meiosis) Reduced development of male characteristics; some feminine characteristics Diagnose with KARYOTYPE

Cri du chat syndrome Missing piece of chromosome 5 (chromosomal mutation during meiosis) Name based on sound of child’s cry (sounds high-pitched, like a cat) Mental retardation, slanted wide-set eyes, microencephaly (small head) Diagnose with KARYOTYPE

Genetic Disorders Which are dominant? Recessive? Which are sex-linked? Which result from chromosomal mutations?

Are Genes Everything? Why do some people have different symptoms of the same disease? What are “identical” twins not exactly alike?

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