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