Chromosomal Mutations

• Three Types of Chromosomal Mutations

  Rearrangements, Aneuploidy, Polyploidy
• Rearrangements


  duplications, deletions, translocations, inversions of segments within the chromosome
• Duplication: cause unbalanced gene dosage which lead to abnormalities, also lead to looping out in heterozygotes, ex. Bar gene in Drosophila
• Deletion: cause Pseudo-dominance which causes a recessive allele to be expressed due to the deletion of a dominant allele, also Haplosufficiency, this is when a gene is too low to affect the wild-type phenotype.
• Inversion: expression is destroyed and can lead to non viable gametes, heterozygous crossing over is decresed
• Translocation: reciprocal and nonreciprocal, can destroy expression and lead to nonviable gametes
• Robertsonian Translocation


  the fusion of two acrocentric chromosomes, ex. human chromosome 2
• Aneuploidy Causes

  nondisjunction during meiosis or mitosis, loss of centromere
• Nullisomy


  loss of two chromosomes (2n - 2)
• Monosomy


  loss of one chromosome (2n - 1)
• Trisomy


  gain of extra chromosome (2n + 1)
• Tetrasomy


  gain of two chromosomes (2n + 2)
• Sex-Linked Aneuploidy

  X or Y is affected, Turner and Klinefelter syndrome
• Autosomal Aneuploidy

  Trisomy 21 - down syndrome

  Trisomy 18 - Edward syndrome

  Trisomy 13 - Patau syndrome
• Polyploidy


  multiple sets of chromosomes, exceeds normal diploid number
• Autoploidy


  the aberrant segregation of chromosomes during mitosis or meiosis
• Alloploidy


  hybridization of two different species, normally sterile, ex. potato, banana