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
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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?