Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

chromatid aberrations. Unlike chromosomal aberrations, only one of the daughtercells will be affected if only one of the chromatids of a pair is damaged.Repair of chromosomal aberrations depends on several factors, including thestage of the cell cycle and the type and location of the lesion. There is a strong forceof cohesion between broken ends of chromatic material. Interchromosomal andintrachromosomal recombination may occur in a variety of ways, yielding manytypes of aberrations such as rings and dicentrics. Figure 25-4 illustrates some of themore common chromosomal aberrations and the consequences of replication and~~.,. .-(-~-.~Breakage Recombination Replication Anaphasic SeparationA. One break In onechromosomeNone---- -~0 Q)B. Two breaks in onechromosomeRingsor.-00-- - .- W--.~ -C. One break in twochromosomesTranslocation~~-( }~ ~~.~~D. One break In twochromosomesDicentricsc:)~t~\c:)•~FIGURE 25-4. Several examples of chromosomal aberrations and the effect of recombinations, replication,and anaphasic separation. A: Single break in one chromosome, which results in centric andacentric fragments. The acentric fragments are unable to migrate and are transmitted to only one ofthe daughter cells. These fragments are eventually lost in subsequent divisions. B: Ring formation mayresult from two breaks in the same chromosome in which the two broken ends of the centric fragmentrecombine. The ring-shaped chromosome undergoes normal replication, and the two (ring-shaped) sisterchromatids separate normally at anaphase-unless the centric fragment twists before recombination,in which case the sister chromatids will be interlocked and unable to separate. C: Translocationmay occur when two chromosomes break and the acentric fragment of one chromosome combineswith the centric fragment of the other and vice versa, or D: the two centric fragments recombine witheach other at their broken ends, resulting in the production of a dicentric.