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Chromosomal Mutations

Chromosomal Mutations. Changes in Chromosome Number or Structure Alterations of Inheritance Patterns by Gender. Alterations in Chromosome Number . Polyploidy: one or more extra sets of chromosomes

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Chromosomal Mutations

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  1. Chromosomal Mutations Changes in Chromosome Number or StructureAlterations of Inheritance Patterns by Gender

  2. Alterations in Chromosome Number • Polyploidy: one or more extra sets of chromosomes • Aneuploidy: gain or loss of one chromosome or a small number of chromosomes

  3. Non-disjunction in Meiosis II Normal Meiosis Non-disjunction in Meiosis I Aneuploidy • Arises by Non-disjunction • Non-disjunction = failure of homologues or chromatids to separate during meiosis

  4. Human Chromosomal Aneuploids Autosomal Aneuploids Trisomy: three copies of one chromosome

  5. Human Autosomal Abnormality How can Down Syndrome occur? Eg. Egg with 2 copies of #21 (24 chromosomes) + Sperm with 1 copy of #21 (23 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes)

  6. Karyotype for Down Syndrome Physical Features Eye fold Palm Crease

  7. 400 300 200 100 0 10 20 30 40 50 Incidence of Down Syndrome Increases with Maternal Age Number per 1000 Births Age of Mother (years)

  8. Which one involves the loss of one chromosome? Which one describes the failure of chromatids to separate in Anaphase II? Which one involves the gain of an extra set of chromosomes? Which is the most specific description for the cause of Down Syndrome? Polyploidy Non-disjunction Aneuploidy Crossing-over Trisomy Applying Your Knowledge

  9. Human Chromosomal Aneuploids Sex Chromosome Aneuploids Sterile female Fertile female Sterile male Fertile male

  10. Human Sex Chromosome Abnormality How can Turner Syndrome occur? 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)

  11. Karyotype for Turner’s Syndrome Non-functional Ovaries From Adult Female with Turner’s Syndrome Normal uterus, tubes and ovaries

  12. Human Chromosomal Aneuploids How can XYY Syndrome occur? One Copy of the X chromosome Two Copies of the Y chromosome Eg.Egg with 1 copy of X (23 chromosomes) + Sperm with 2 copies of Y (24 chromosomes)= Embryo with XYY (47 chromosomes)

  13. 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

  14. Applying Your Knowledge Determine how many Barr bodies would be found in each cell of someone with: 0 2 1 0

  15. Chromosome Structure Changes

  16. Chromosome Deletion in Humans Cri-du-chat syndrome is correlated with a deletion at the end of chromosome 5.

  17. Chromosome Duplication in Humans • Small duplications in chromosome 15 cause no symptoms • Large duplication (with inversion) causes seizures and mental retardation

  18. Chromosome Translocation in Humans • Reciprocal Translocation involves exchange between two non-homologous chromosomes • Reciprocal translocation between chromosomes 2 and 20 causes Alagille Syndrome

  19. Chromosome Translocation in Humans • Robertsonian Translocation involves a fusion of the long arms of two different chromosomes • Translocation Down Syndrome involves a Robertsonian Translocation between chromosomes 14 and 21

  20. Chromosome Inversions Lead to Unbalanced Meiotic Products A paracentric inversion does not include the centromere A pericentric inversion includes the centromere

  21. Applying Your Knowledge • Deletion • Duplication • Inversion • Translocation • Which type of structure change • represents an exchange between two non-homologous chromosomes? • represents a reversal of a chromosome segment? • represents a loss of a chromosomal segment?

  22. John Adams BB or Bb bb BB or Bb bb John Quincy Adams Interaction between Gender and Heredity Example: Pattern BaldnessCaused by a dominant allele in males,but a recessive allele in females

  23. Interaction between Gender and Heredity Cock-feathered male Hen-feathered female Hen-feathered male Cock feathering, autosomal recessive Expressed only in males

  24. Interaction Between Gender and Heredity Angelman SyndromeDeletion on chromosome 15 inherited from mother Prader-Willi SyndromeDeletion on chromosome 15 inherited from father

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