Cytogenetics

Cytogenetics

1. Chromosome number changes

   • Polyploidy
     • More than 2 sets of chromosomes
     • Autopolyploids: the chromosome sets are all identical; all chromosomes are derived from the same species
     • Many polyploids are sterile, due to problems with pairing and separation of homologous chromosomes in meiosis
     • Allopolyploids: result of crosses between 2 or more (usually related) species
     • Tissue specific polyploidy
       • Endomitosis: sister chromatids separate but no cytokinesis occurs; results in tetraploid cells- liver and kidney cells
   • Aneuploidy
     • Diploid genome which lacks a chromosome or has an extra chromosome
     • Can be caused by meiotic nondisjunction

2. Autosomal Trisomies

3. Chromosome Structural Changes

   • Chromosome Identification: size, centromere position, banding patterns produced by different strains
   • Deletions: Two breaks in a chromosome. A small piece of chromosome is lost. The larger pieces rejoin
     • Effects depend on size of deletion
     • Intragenic deletions: deletions within a gene typically inactivate the gene - NULL mutation
     • Multigenic deletions: involve deletions of 2 to thousands of genes - produce Deletion Syndromes
   • Duplications: Extra copy of gene or chromosomal region; duplicate regions can be located adjacent to each other, or one can be located in the normal location and the other in a novel location
     • Extra regions can undergo gene mutation - opportunity for divergence in function
   • Inversions
   • Translocations
     • Reciprocal Translocations
     • Robertsonian Translocations
     • Unidirectional Translocations
     • Some translocations are associated with cancer