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Chapter 7

Chapter 7. Mendel’s Laws Predict the inherited traits Exceptions to Mendel’s Laws X inactivation turns off entire chromosomes but genomic imprinting turns off specific genes Now we will look at … Disease causing genes (both autosomal and sex linked disorders).

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Chapter 7

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  1. Chapter 7 • Mendel’s Laws • Predict the inherited traits • Exceptions to Mendel’s Laws X inactivation turns off entire chromosomes but genomic imprinting turns off specific genes Now we will look at … Disease causing genes (both autosomal and sex linked disorders)

  2. Are sex chromosomes present in your skin cells? • Yes • No

  3. 22 pairs of non-sex chromosomes and 1 pair of sex chromosomes

  4. Human Genetic Disorders (> 1000; controlled by a single gene) X- linked Disorders Autosomal Disorders dominant recessive recessive Dominant

  5. Autosomal Recessive disorders -more common -homozygous recessive to show symptoms -heterozygous…..carriers -Example: Cystic fibrosis, sickle-cell, Tay-Sachs disease, Fanconi anemia

  6. Cystic Fibrosis Autosomal recessive (CF gene on chromosome 7)

  7. If the father is a carrier for cystic fibrosis and the mother is normal, what are the chances that their child will have the disease ? • 100% • 50% • 25% • 0%

  8. Autosomal Dominant disorder -Much less common -Some are nonlethal while others are lethal -Examples: Achondroplasia Huntington’s disease Fatal familial insomnia Osteogenesis imperfecta

  9. Huntington’s Disease Cause: Autosomal dominant gene H h h Hh hh Hh hh h A person with Huntington’s disease has a ______ chance of passing the disorder on to their offspring.

  10. Can you carry the allele for an autosomal dominant disorder and not show the symptoms? • Yes, b’cos 2 copies are needed to show symptoms B. No, b’cos only 1 copy is needed to show symptoms

  11. Human Genetic Disorders (> 1000; controlled by a single gene) X- linked Disorders Autosomal Disorders dominant recessive Dominant recessive

  12. X linked recessive traits– more men have this disorder than women. Hemophilia Color blindness Muscular Dystrophy X linked traits can be dominant! more women have this disorder than men! Very rare: Vit D resistant ricketts Rett syndrome

  13. Hemophilia is a recessive sex linked trait. What is the genotype of … • A normal woman whose father had hemophilia • A normal man whose father had hemophilia

  14. X linked dominant Rett syndrome -affected male is lethal

  15. Fetal testing Detect inherited disorders in pregnancy using: • Amniocentesis • Chorionic villus sampling • Ultrasound imaging

  16. A woman who is a carrier for the recessive, sex-linked trait red color blindness, marries a normal male. What is the chance that their daughters will be color blind? • All • 50 % • 25% • 0 • 75%

  17. Using pedigrees to decipher and predict the inheritance patterns of genes. Pedigree a type of family tree

  18. Sex-Linked Traits

  19. XN = normal allele Xn = colorblindness allele

  20. Is George colorblind? • Yes • No

  21. Autosomal dominant

  22. Autosomal Recessive

  23. Sex-Linked Recessive

  24. Individual Activity (5 pts) The following pedigree follows a sex linked recessive trait. Circle all of the persons you are certain are carriers. Carriers are people who carry the allele but show/express no symptoms. Hint: Only 4 people

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