Oregon State University

Genome Architecture

Genome Remodeling: re-arrangements, changes, and expansions

I. Re-arrangements

A. Overview and key points

  • Chromosome aberrations are the basis of cytogenetic analysis.
  • Chromosome rearrangements are a gross form of mutation. If critical genetic information is lost, the aberration won't survive.
  • Certain genome architectures, such as polyploidy, allow for the maintenance of chromosome aberrations that would otherwise be lethal in a diploid.
  • For rearrangements that are not lethal, chromosome breakage and rearrangement can lead to new linkage relationships.

 

B. Types of chromosome aberrations:

The principal classes of chromosome rearrangements are duplications/deficiencies, inversions  and translocations.

  • L-1. A graphical summary of the principal types of chromosome rearrangements. Know the what, how, and consequences.

1. Duplications/Deficiencies:

In plants, deficiencies usually abort while duplications will not. Deficiency heterozygotes are usually semi-sterile.

2. Inversions: The event; meiosis

  • L-2. Visual reinforcement of what, how, and consequences.

 

Inversions occur when there are two breaks in the chromosome, followed by reverse insertion. If there is no crossing over within the loop of an inversion heterozygote, gametes will be viable. If there is crossing over within the loop, sterility may result due to chromosomal aberrations produced as a result of the crossover. Different types of crossovers will create different aberrant chromosomes.

3. Translocations: The event; meiosis

  • L-2. Visual reinforcement of what, how, and consequences.

Translocations occur when there are breaks in non-homologous chromosomes followed by translocation of the non-homologous fragments

 

II. Expansions

A. Overview and key points

  • Transposable elements (a.k.a. "jumping genes", "mobile elements") are discrete elements of DNA with the capacity to excise and insert themselves into other sites in their host’s DNA.
  • Where the element inserts itself (i.e. in an exon, in an intron, near a gene, or outside of a gene) will dictate what, if any, effect there will be on a phenotype. 
  • Elements have primary responsibility for the C-value paradox (enigma).
  • Transposable elements are a principal component of the "junk" DNA that accounts for differences in genome size. But is the "junk" really junk?
  • Transposable elements are "selfish DNA" since they are "parasitic" - they make copies of themselves. If they produce a phenotype, it is by "commandeering" the host genome. But perhaps they are not really parasitic - maybe symbiotic?
Next Section
  • C-value. L-2. Remember Kew gardens

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