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Human Genetics

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?

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Human Genetics

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  1. Human Genetics

  2. Human Chromosomes • 23 Pairs - 22 Autosomes - 1 Sex chromosome • 1 set contributed by mother • 1 set contributed by father

  3. 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

  4. When does nondisjunction happen?

  5. 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

  6. Normal Karyotypes 46, XX 46, XY

  7. 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.

  8. 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

  9. Klinefelter’s Syndrome - 47, XXY • Characteristics - Male sex characteristics - Underdeveloped testes - Sterile - Some female secondary sex characteristics (breast and hip growth)

  10. Can you tell what is going on in this karyotype?

  11. Can you tell what is going on in this karyotype?

  12. Patau Syndrome • Trisomy 13 - Severe mental and physical problems - Cleft lip, palate, small head, heart problems, small limbs

  13. What is wrong here and what would be the notation?

  14. Edwards Syndrome • Trisomy 18 - Severe mental and physical disabilities - Rarely live past one year

  15. What is wrong here?

  16. Other Chromosomal Disorders • Translocations : Philadelphia Translocation t(9;22)(q34;q11.2) • Deletions : Fragile X, Cri du Chat • Duplications : Rare

  17. Cri du Chat Syndrome • High pitch cry (cat like) • Downward eye slant • Mental retardation • Partially webbed fingers or toes • Small head and eyes

  18. Following Traits : Pedigrees • Chart showing relationships and tracing a particular trait through a family

  19. Autosomal Dominant • Appears in every generation • An afflicted child must have an afflicted parent

  20. 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

  21. Other Dominant Diseases • Achondroplasia – Dwarfism • Hypercholesterolemia – high cholesterol • Osteogenesis imperfecta – brittle bones • Polydactyly – 6 fingers and toes • Many others

  22. Recessive Disorders • Appears intermittently through generations (up to 25% of individuals) • No sex preference • Afflicted child does not necessarily have an afflicted parent

  23. 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

  24. Example: Cystic Fibrosis • Thick, sticky mucous • Effects all secretory organs • CFTR protein has a single AA change

  25. Other Recessive Disorders • Phenylketonuria – accumulation of phenylalanine in tissues • Tay-Sachs disease – lipid accumulation in brain cells • Galactosemia – inability to metabolize galactose • Many others

  26. Codominant disorder: Sickle cell anemia • NN = normal hemoglobin Nn = sickle cell trait nn = sickle cell anemia • Evolution: Library: A Mutation Story

  27. Sex-Linked Inheritance • Trait only (usually) expressed in males • Skips generations in families

  28. Hemophilia in the Royal Family

  29. Other sex-linked recessive disorders • Duchene muscular dystrophy • Red-green colorblindness • Fragile-X syndrome

  30. Imprinting and Disorders PraderWilli Syndrome Angelman Syndrome

  31. Blue people of Troublesome Creek

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