Ch.15 genetics ii

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Ch.15 genetics ii

  1. 1. Genetics - part two Chapter 15
  2. 2. Review• Genes are located on chromosomes• Diploid organisms have two copies of every chromosome• Therefore, two alleles for every gene (except X,Y)
  3. 3. Chromosomal basis of Mendel’s Laws• Meiosis• Segregation• Independent assortment
  4. 4. Fruit Flies
  5. 5. Fruit Flies in Genetics• Small genome – 4 chromosomes• Short generation time• Wild type – most common phenotype – Red eyes• Studies revealed – Sex-linked genes
  6. 6. Sex-linked Inheritance
  7. 7. Gene Recombination & Crossing Over
  8. 8. Constructing a Gene MapThe farther two genes are from each other, thehigher the probability that crossing over will occurbetween them. This can be used to figure outwhere genes are on the chromosome.
  9. 9. Some chromosomal systems of sex determination
  10. 10. Sex-linked Inheritance
  11. 11. Inactivation of the X & Barr Bodies• One X is inactivated during development – becomes Barr body• Same X is not inactivated in all cells• Mosaic in heterozygotes
  12. 12. Nondisjuction (during Meiosis)
  13. 13. Down Syndrome
  14. 14. Genetic disorders caused by abnormal chromosome number (due to nondisjunction)Name Chromosome DescriptionDown syndrome 21 TrisomyEdward’s syndrome 18 TrisomyPatau syndrome 13 TrisomyTurner’s syndrome Single X XOKlinefelter’s syndrome Extra X (in males) XXYXYY syndrome Extra Y (in males) XYYTriple X syndrome Extra X (in females) XXX
  15. 15. Alterations of Chromosomes
  16. 16. Genomic Imprinting• Some genes behave differently if they come from ova/ sperm• One gene can be “silenced” and the other is expressed• Imprinting is not inherited• Genes are re-imprinted for in the next generation
  17. 17. Example: Imprinting• Prader-Willi/ Angelman syndromes• Deletion on chromosome 15• If inherited from father – Prader-Willi syndrome • Mental retardation, obseity, short stature, small hands and feet• If inherited from mother – Angelman syndrome • Spontaneous uncontrollable laughter, jerky movements, motor and mental problems

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