Effects of Radiation on Chromosomes

Chrom o some damage can be:

 m o rphologically visible, e.g., changes in num ber or structure

 or not vi si ble but with func tional consequences: m u tations.

Methods of chrom o some analysis:

 Standard staining aft e r adding an agent that blocks m itosis in metaphase.

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 Banding techniques: various techniques to stain the chrom o somes produce visible bands.

 Incorporation of [ 3 H]Thd followed by autoradiography.

Techniques to look at chromosome aberrations

Premature ch romosome cond ensation :

 Irradiate cells

 Fuse irradiated cells with m itotic cells

 Factors in the m itotic cells force the chromoso mes of the irradiated interphase cells to co ndense.

 This visualizes all d a mage including some that may have been repaired.

 Visualizes severe damage that may ha ve been detected before m itosis and prevented the cell fro m entering m itosis.

Fluorescence in situ hybridiz ation (FISH):

Uses fluorescently tagged chromoso me p r obes (compli m entary DNA) t o specific chrom o somes or regions of chrom o som e s.

Types of chromosome dama ge observ ed

 Term inal deletions

 Intrachromoso me exchange

 Interchrom osome exchange

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[Image removed due to copyright considerations]

Chromosome aberrations and cell d e ath

 Chromosome aberrat i ons can be detect ed after doses as low as 0.1 Gy.

 Chrom o some aberrations reflect both the initial damage and the repair. (m isrepair), because the chromosom e s are not visible until the cells enter m itosis.

 Doses in the 0.5 – 2 Gy range, prod uce on the average one chr o moso me aberration per cell.

 This dose range is, on the average, the mean lethal d o se for cel ls.

 The frequency of chrom o som e aberrations is a linear quadratic function of radiation dose.

 There are considerable data showing a relationship betw een cell killing and the inducti on of chrom o some aberrations.

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Historically, these led to the th eory of dual radiation action.

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Cell cycl e import ance:

The state of the chrom o so mes a ffects the radiation sensitivity.

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[Image removed due to copyright considerations]