Cytogenetics

Cytogenetics

Chromosome number changes
1. Polyploidy
  1. More than 2 sets of chromosomes
  2. Autopolyploids: the chromosome sets are all identical; all chromosomes are derived from the same species
  3. Many polyploids are sterile, due to problems with pairing and separation of homologous chromosomes in meiosis
  4. Allopolyploids: result of crosses between 2 or more (usually related) species
  5. Tissue specific polyploidy
    1. Endomitosis: sister chromatids separate but no cytokinesis occurs; results in tetraploid cells- liver and kidney cells
2. Aneuploidy
  1. Diploid genome which lacks a chromosome or has an extra chromosome
  2. Can be caused by meiotic nondisjunction
Autosomal Trisomies
Chromosome Structural Changes
1. Chromosome Identification: size, centromere position, banding patterns produced by different strains
2. Deletions: Two breaks in a chromosome. A small piece of chromosome is lost. The larger pieces rejoin
  1. Effects depend on size of deletion
  2. Intragenic deletions: deletions within a gene typically inactivate the gene - NULL mutation
  3. Multigenic deletions: involve deletions of 2 to thousands of genes - produce Deletion Syndromes
3. 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
  1. Extra regions can undergo gene mutation - opportunity for divergence in function
4. Inversions
5. Translocations
  1. Reciprocal Translocations
  2. Robertsonian Translocations
  3. Unidirectional Translocations
  4. Some translocations are associated with cancer

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