Chromosome numbers

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Chromosome numbers

• Somatic chromosome number (2n) This is the
  number of chromosomes observed in a body cell
  (somatic cell). It is used to indicate mitotic
  results. NB It is not a diploid chromosome
  number as suggested by certain prescribed books!
• Gametic chromosome number (n) This is the number
  of chromosomes observed in a male gamete of an
  individual. It is used to indicate results from
  a meiotic study. It is not always half the
  number of chromosomes in a somatic cell! (Rosa
  canina).
• Basic chromosome number (x) It is the lowest
  gametic chromosome number in a taxon.

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Aneuploidy

• Gain or loss of a chromosome or chromosomes from
  a genome
• 1 2 3 4 5 / 1 2 3 4 5
• 1 2 3 4 5 / 1 2 4 5
• loss aneuploidy
• Monosomic 3
• 2n2x-19

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Problem

• Rye has a chromosome complement of 2n2x14. You
  cross a monosomic 2 rye with a trisomic 4 plant.
  What will the chromosome numbers and chromosome
  constitution of the offspring be?

4

• Monosomic 2 1 2 3 4 5 6 7 / 1 3 4 5 6 7
• Trisomic 4 1 2 3 4 5 6 7 / 1 2 3 4 4 5 6 7

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Dysploidy

• Decrease in the chromosome number without loss of
  genetic material
• Robertsonian translocation
• 2n2xD9

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Polyploidy

• Addition of a whole genome or genomes to the
  chromosome complement
• Di- tri-, tetra-, penta-, hexa-, hepta-, octa-,
  nona-, decaploid
• Auto-, allo-, auto-allo-, segmental alloploidy

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Problem

• The following four species are studied
  cytogenetically
• X ? 10II Y ? 15II Z ? 5IV10II W ?
  10IV10II.
• After crossings the following results are
  obtained
• X x Y ? 5II15I X x Z ? 5III15I
• X x W ? 5III10II5I Y x Z ? 15II5I
• Y x W ? 10III5II5I Z x W ? 10III10II
• Determine the genomic constitutions of X, Y, Z
  and W.

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Problem

• You did a cytogenetic study of four species and
  their hybrids. What are the genomic
  constitutions of each species if you obtain the
  following results
• K 10II L 5IV5II
• M 5IV5II N 15II
• KL 10II5I KM 5III10I
• KN 10II5I LM 5III5II5I
• LN 5III5II5I MN 5III5II5I

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Problem

• Name the type of polyploidy present in each case,
  the organisms genomic constitution and discuss
  the terms used
• 22 model with x0.5 (Also give a synonym for
  this model)
• 221 model with x 0.7
• A plant with 2n3x15 that forms 5II5I
• A plant with 2n3x15 that forms 5III
• A plant with 2n3x15 that forms 3III6I