Changes in Chromosome Number

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

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Nondisjunction
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Aneuploidy in Plants Seed Capsule Changes Due to
Trisomy in Jimson Weed
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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

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Down Syndrome Karyotype and Physical Features
Eye fold
Palm Crease
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Incidence of Primary Down Syndrome Increases with
Maternal Age
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Robertsonian Translocation Carrier of Down
Syndrome
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Chromosome Segregation in a Translocation Carrier
Expected Result 1/3 carrier 1/3 normal 1/3
Down Syndrome
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Human Sex Chromosome Aneuploidy
XO
Sterile Female
Sterile Male
XXY
XXX
Fertile Female
Fertile Male Taller
XYY
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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)
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Turner Syndrome Karyotype and Physical Features
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Non-functional Ovaries From Adult Female with
Turner Syndrome
Child with Turner Syndrome
Normal uterus, tubes and ovaries
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Human Sex Chromosome Aneuploidy
Klinefelters 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)
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Klinefelter Syndrome Karyotype and Physical
Features
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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
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Applying Your Knowledge

• Nullisomic
• Monosomic
• Disomic
• Trisomic

Which term describes the chromosome number
change for individuals with A. Down
Syndrome? B. Turner Syndrome?
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Applying Your Knowledge
Zero fist One Two Three
How many Barr bodies would be found in cells
of individuals with A. Klinefelter
Syndrome? B. Turner Syndrome? C. Triple-X
Syndrome?
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Polyploid Numbers
Polyploid euploid organism with more than
two sets of chromosomes
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Types of Polyploids
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Polyploidy Arises by Nondisjunction
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Chromosome Segregation in Polyploids Leads to
Unbalanced Gametes
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Production of modern wheat

• Is T. aestivum
• Autopolyploid?
• Allopolyploid?

• Euploid?
• Aneuploid?