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?

• http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Lectures/Genetics-%20Genes/mendelia.htm