The regions of synteny between the chromosomes of two species can be visualized in dot plots. In the example shown in the following graph, a chromosome of a hypothetical species A has been aligned with the related chromosome in species B. Each dot in the plot represents the observation of high sequence identity between the two aligned chromosomes in a window located at the two corresponding chromosome positions. A series of close dots can make a continuous line. Choosing a sufficiently large window size allows a "clean" dot plot with solid lines that show only the long stretches of identity, allowing ancient large-scale rearrangements to be identified. Several chromosomal events can be detected in such dot plots. Indicate which feature (a to g) in the dot plot is best explained by each of the following events. Your answer would be a seven-letter string composed of letters a to g only, e.g. cdbagef. Each letter should be used only once.

( ) A duplication that exists in both species
( ) A duplication in species A only
( ) A triplication in species B only
( ) An inversion without relocation
( ) An inversion combined with relocation
( ) A deletion in species A
( ) A translocation in species A from a different chromosome

Question

The regions of synteny between the chromosomes of two species can be visualized in dot plots. In the example shown in the following graph, a chromosome of a hypothetical species A has been aligned with the related chromosome in species B. Each dot in the plot represents the observation of high sequence identity between the two aligned chromosomes in a window located at the two corresponding chromosome positions. A series of close dots can make a continuous line. Choosing a sufficiently large window size allows a "clean" dot plot with solid lines that show only the long stretches of identity, allowing ancient large-scale rearrangements to be identified. Several chromosomal events can be detected in such dot plots. Indicate which feature (a to g) in the dot plot is best explained by each of the following events. Your answer would be a seven-letter string composed of letters a to g only, e.g. cdbagef. Each letter should be used only once.
  
( ) A duplication that exists in both species 
( ) A duplication in species A only 
( ) A triplication in species B only 
( ) An inversion without relocation 
( ) An inversion combined with relocation 
( ) A deletion in species A 
( ) A translocation in species A from a different chromosome

Quizplus · Accepted Answer

A diagonal line in this plot indicates a continuous region of synteny between the two chromosomes. Because of a genomic region that is absent (e.g. deleted) from one end of the chromosome of species A, the long diagonal line is shifted up (represented by a in the plot). A symmetrical set of parallel lines (as at b) on the two sides of a diagonal reflects the existence of a repeat in both chromosomes, whereas the parallel line on one side of the diagonal at c indicates duplication only in species A. A chromosomal inversion shows up as a diagonal with a negative slope, which may or may not be accompanied by translocation of the inverted region (as at d and e, respectively). Two tandem duplications in species B may appear as a triplication (as at f) represented by three parallel lines. Finally, g represents a region at the end of the chromosome in species A that is absent from the chromosome of species B.

The Regions of Synteny Between the Chromosomes of Two Species