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Human Genetics Human Chromosomes • 23 Pairs • • - 22 Autosomes - 1 Sex chromosome 1 set contributed by mother 1 set contributed by father Chromosomal disorders • How many chromosomes does a normal human gamete have? • What happens if a gamete fails to separate chromosomes properly? - Nondisjunction – results in…. - Aneuploidy – any difference from the normal 46 chromosomes When does nondisjunction happen? How do you diagnose nondisjunction? Karyotyping • Picture of the • chromosomes Sample collected by Amniocentesis in at risk mothers - mothers over 35 - families with histories of genetic disorders Normal Karyotypes 46, XX 46, XY Nondisjunction disorders • Down Syndrome • - Extra copy of the 21st Chromosome - 47, X_, +21 - 1/700 live births in the US Characteristics - characteristic facial features, short stature; heart defects - susceptibility to respiratory disease, shorter lifespan - prone to developing early Alzheimer's and leukemia - often sexually underdeveloped and sterile, usually some degree of mental retardation. - Down Syndrome is correlated with age of mother but can also be the result of nondisjunction of the father's chromosome 21. Nondisjuncton in sex chromosomes • Turner’s Syndrome (Monosomy X) • - 45, X - 1/5000 live births Characteristics - short stature - characteristic “webbed” neck - infertile - normal mental development • Klinefelter’s Syndrome - 47, XXY • Characteristics - Male sex characteristics - Underdeveloped testes - Sterile - Some female secondary sex characteristics (breast and hip growth) Can you tell what is going on in this karyotype? Can you tell what is going on in this karyotype? Patau Syndrome • Trisomy 13 - Severe mental and physical problems - Cleft lip, palate, small head, heart problems, small limbs What is wrong here and what would be the notation? Edwards Syndrome • Trisomy 18 - Severe mental and physical disabilities - Rarely live past one year What is wrong here? Other Chromosomal Disorders • Translocations : Philadelphia Translocation t(9;22)(q34;q11.2) • Deletions : Fragile X, Cri du Chat • Duplications : Rare Cri du Chat Syndrome • High pitch cry (cat • • • • like) Downward eye slant Mental retardation Partially webbed fingers or toes Small head and eyes Following Traits : Pedigrees • Chart showing relationships and tracing a particular trait through a family Autosomal Dominant • Appears in every generation • An afflicted child must have an afflicted parent Example: Huntington’s Disease • Autosomal dominant CAG • • • • repeat Degeneration of nerves Person begins life normally Nerves degenerate over time Jerky motion, slurred speech, mental retardation Other Dominant Diseases • Achondroplasia – Dwarfism • Hypercholesterolemia – high cholesterol • Osteogenesis imperfecta – brittle bones • Polydactyly – 6 fingers and toes • Many others Recessive Disorders • Appears intermittently through generations (up to 25% of individuals) • No sex preference • Afflicted child does not necessarily have an afflicted parent Example : Albinism • Lack of pigment in • • skin, hair and eyes No common negative health problems besides increased risk of skin cancer Defective gene for the production of melanin Example: Cystic Fibrosis • Thick, sticky mucous • Effects all secretory organs • CFTR protein has a single AA change Other Recessive Disorders • Phenylketonuria – accumulation of phenylalanine in tissues • Tay-Sachs disease – lipid accumulation in brain cells • Galactosemia – inability to metabolize galactose • Many others Codominant disorder: Sickle cell anemia • NN = normal • hemoglobin Nn = sickle cell trait nn = sickle cell anemia Evolution: Library: A Mutation Story Sex-Linked Inheritance • Trait only (usually) • expressed in males Skips generations in families Hemophilia in the Royal Family Other sex-linked recessive disorders • Duchene muscular dystrophy • Red-green colorblindness • Fragile-X syndrome Imprinting and Disorders Prader Willi Syndrome Angelman Syndrome Blue people of Troublesome Creek