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Changes in Chromosome Number

Changes in Chromosome Number . Chromosome Number Mutations. Euploid = organism with multiples of the number of chromosomes in a basic set . Aneuploid Numbers. n = haploid number of chromosomes 2n = diploid number of chromosomes. Causes of Aneuploidy.

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Changes in Chromosome Number

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  1. Changes in Chromosome Number

  2. Chromosome Number Mutations Euploid = organism with multiples of the number of chromosomes in a basic set

  3. Aneuploid Numbers n = haploid number of chromosomes 2n = diploid number of chromosomes

  4. Causes of Aneuploidy • Loss of a chromosome that has a centromeric deletion • Loss of the small chromosome produced by Robertsonian translocation • Nondisjunction = failure of homologs to separate during meiosis or chromatids to separate during meiosis or mitosis

  5. Nondisjunction

  6. Aneuploidy in Plants: Seed Capsule Changes Due to Trisomy in Jimson Weed

  7. Human Autosomal Aneuploidy • Most common type is Down Syndrome: Trisomy 21 • Arises in two ways • Primary Down Syndrome • Due to nondisjunction in egg formation • Egg with 2 copies of #21(24 chromosomes) • + Sperm with 1 copy of #21(23 chromosomes)= Embryo with 3 copies of #21(47 chromosomes) • Familial Down Syndrome • Inherited from a carrier of a Robertsonian Translocation involving chromosome 21

  8. Down Syndrome Karyotype and Physical Features Eye fold Palm Crease

  9. Incidence of Primary Down Syndrome Increases with Maternal Age

  10. Translocation of 21q to 15q Robertsonian Translocation Carrier of Down Syndrome

  11. Chromosome Segregation in a Translocation Carrier Expected Result: 1/3 carrier + 1/3 normal + 1/3 Down Syndrome

  12. Human Sex Chromosome Aneuploidy XO XXY XXX XYY

  13. Human Sex Chromosome Aneuploidy Turner Syndrome One Copy of X chromosome No second sex chromosome Eg. Egg with 0 copies of X(22 chromosomes)+Sperm with 1 copy of X(23 chromosomes)= Embryo with 1 copy of X(45 chromosomes)

  14. Turner Syndrome Karyotype and Physical Features

  15. Non-functional Ovaries From Adult Female with Turner Syndrome Child with Turner Syndrome Normal uterus, tubes and ovaries

  16. Human Sex Chromosome Aneuploidy Klinefelter’s Syndrome Two Copies of the X chromosome One Copy of the Y chromosome Eg. Egg with 2 copies of X(24 chromosomes)+ Sperm with 1 copy of Y(23 chromosomes)= Embryo with XXY(47 chromosomes)

  17. Klinefelter Syndrome Karyotype and Physical Features

  18. X-Chromosome Inactivation in Females • Inactivation of one of the X chromosomes in each cell of an adult female balances the sex chromosome/autosome ratio. • Either the maternal or paternal chromosome is inactivated. • The arrow shows a Barr body, or inactivated X. • The number of Barr bodies equals the number of X chromosomes minus one. female male

  19. Polyploid Numbers Polyploid = euploid organism with more than two sets of chromosomes

  20. Types of Polyploids

  21. Polyploidy Arises by Nondisjunction

  22. Chromosome Segregation in Polyploids Leads to Unbalanced Gametes

  23. Production of modern wheat

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