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Human Pedigree and Genetic Disease

Human Pedigree and Genetic Disease. Gregor Mendel. Thomas Bayes. Common Pedigree Symbols. Male. Marriage. Female. Sex Unknown. Consanguineous Marriage. Affected Female. No Known Pregnancy. Female Carrier of Sex-linked Recessive. Unmarried. Female Carrier (Heterozygous).

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Human Pedigree and Genetic Disease

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  1. Human Pedigree and Genetic Disease Gregor Mendel Thomas Bayes

  2. Common Pedigree Symbols Male Marriage Female Sex Unknown Consanguineous Marriage Affected Female No Known Pregnancy Female Carrier of Sex-linked Recessive Unmarried Female Carrier (Heterozygous) Divorce and Remarried Dead

  3. Common Pedigree Symbols Pregnancy in Progress Dizygotic (nonidentical, fraternal) twins Three Males 3 Five Individuals (both sexes) Monozygotic (identical) twins 5 Spontaneous Abortion Adopted Child Proband, propositus, or index case

  4. Happy new wife! Famous Kid Bad Divorce Triplets!

  5. Mistakes in Meiosis • Chromosomes fail to separate properly during meiosis, i.e., nondisjunction • ANEUPLOIDY -- an abnormal number of chromosomes • Examples: • Down’s Syndrome (Trisomy-21) • Klinefelter’s Syndrome • Turner’s Syndrome

  6. Polygenic Inheritance • Most human characteristics are polygenic, meaning they are influenced by several genes, e.g. skin color influenced by 3-6 genes; also, eye color, height, hair color • Complex characters are those that are influenced strongly by both the environment and genes, e.g., diabetes, heart disease, stroke, skin color, height

  7. More patterns of inheritance….. • Multiple alleles - genes with three or more alleles, e.g., ABO blood groups • Incompletedominance – condition that results in a display of a trait that is intermediate between the two parents • X-linkedtraits – determined by x-linked genes, e.g., color blindness • Sex-influencedtraits – usually autosomal, e.g. baldness is influenced by testosterone • Single-allele traits – more than 200 human traits are governed by single dominant alleles, e.g., Huntington’s disease

  8. Detecting Genetic Disease • Genetic Screening – examination of a person’s genetic makeup involving karyotypes, blood tests for certain proteins, or direct tests of DNA • 200 genetic disorders can be detected in the fetus • Amniocentesis – removal of amniotic fluid from the sac that surrounds the fetus between the 14th and 16th week of pregnancy • Chorionic villi sampling – sample of cells derived between the 8th and 10th week from the zygote - cells grow between the mother’s uterus and the placenta; cells chromosomes, and proteins analyzed

  9. Detecting Genetic Disease • Chorionic villi sampling – CVS can help identify chromosomal problems such as Down syndrome or other genetic diseases such as cystic fibrosis, Tay-Sachs disease and sickle cell anemia. CVS is considered to be 98% accurate in the diagnosis of chromosomal defects, such as Down syndrome.

  10. Normal Female Karyotype

  11. Normal Male Karyotype

  12. Down’s Syndrome • Smallest chromosomes with 1500 genes affected. • Occurs in 1 out of every 800 babies. • 40% congenital heart defects. • Can result from maternal age or chromosome defect.

  13. Klinefelter’s Syndrome • Occurs in one out of every 1000 males. • Results from extra X chromosome = XXY. • Males tall, sterile, small testicles, and mentally handicapped.

  14. Turner’s Syndrome • Occurs in females. • Results from XO condition. • Female is short, sterile, and mentally impaired.

  15. Single Gene Inheritance Pedigree Analysis • Autosomal dominant traits • Huntington’s Disease on chromosome #4 • Marfan Syndrome on chromosome #15 • Breast Cancer on chromosomes #17 • Autosomal recessive traits • Tay-Sachs Disease on chromosome #15 • Cystic Fibrosis on chromosome #7 • Sickle Cell Anemia on chromosome #11 • X-Linked Disease (Sex-Linked) • Hemophilia --Duchenne’s muscular dystrophy • Color Blindness

  16. Autosomal Dominant Traits • Present on any autosomal chromosome, i.e., 1-22. • One allele present = disease present, i.e., a person has it or he or she does not

  17. Huntington’s Disease • Begins to show up by age 45-55, within 10-20 years, death is eminent. • Progressive degeneration of nervous system; irregular body movements and slurred speech. • If one parent has HD, offspring have 50% chance of inheriting disease. • Autosomal dominant on chromosome 4; 1 in 10,000 births

  18. Huntington’s Disease Hh hh What are the genotypes of the parents?

  19. Marfan Syndrome • Symptoms: long limbs, loose joints, deformed vertebral column, crowded teeth, rupture of large arteries • 1 in 20,000 Americans born with it • Caused by lack of fibrillin-1, a major component of connective tissue found in ligaments and blood-vessel sheaths

  20. Autosomal Recessive • Disease manifests itself if offspring inherits one recessive gene from each parent. • If parents are carriers, 25% of offspring will have disease.

  21. Tay-Sachs Disease • 1 in 600 Jews of European descent born with it • Lipids deposited in nervous system, causing brain to be damaged -- blindness, loss of movement, mental deterioration. • No break down of cellular wastes in lysosome due to absence of hexosaminidase A – mutation causes nerve death • Symptoms appear around 6 months of age and victims die due to paralysis and/or convulsions before the age of five.

  22. Tay-Sachs Disease Tt Tt tt TT or Tt Tt or TT Tt or TT What are the genotypes of all individuals in this family? TT or Tt Tt Tt tt

  23. Cystic Fibrosis • Found in Caucasians. • Most common lethal genetic disorder among white Americans. • Autosomal recessive on chromosome 7 • Thick mucus produced in lungs, intestines, and pancreas. • 1/20 of Caucasian population are carriers. • One in 2,000 children born to white Americans inherits the disorder. • CF kills ~500 children and young adults each year.

  24. Sickle Cell Anemia • Found in both African Americans and Hispanics of Carribbean ancestry (1 in 500 African Americans) • Hemoglobin (oxygen-carrying protein) differs by ONE amino acid. • Sickling of cells occurs, clogging vessels -- stroke. • In U.S., 60,000 people have it; 30 million carriers. • Autosomal recessive on chromosome 11

  25. X-Linked Disorders • Found on the 23rd pair of chromosomes, i.e., the sex chromosomes. • Usually shows up in males due to Y chromosome lacking genes, i.e., one recessive gene in males produces disorder. • Mother carriers pass gene to sons.

  26. Hemophilia -- “Bleeder’s Disease” • Deficient blood coagulation due to absence of coagulation factor 8 that helps cause blood to clot. • 50% of daughters will also be carriers. • 1 in 7,000 born with it • X-linked recessive on chromosome X XHXh XHY

  27. Duchenne’s Muscular Dystrophy • Progressive destruction of muscles. • Patients wheelchair bound by teens. • Female carriers can be detected by presence of creatine kinase. • Can be detected by the 20th week of gestation.

  28. Duchenne’s Muscular Dystrophy XDXd XDY

  29. Color Blindness

  30. Red-Green Color Blindness

  31. Multiple Alleles • Blood type, using I gene. • Human blood types include: Phenotype Genotype • AIAIA or IAi • BIBIB or IBi • ABIAIB (Universal Recipient) • Oii (Universal Donor) If a child has type O blood and its mother has type A, could a type B man be the father? Why couldn’t a blood test be used to prove he is the father?

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