The effect of x-rays on chromosome structure

✍ Scribed by Sax, Karl

• Publisher: Wiley (John Wiley & Sons)
• Year: 1950
• Tongue: English
• Weight: 508 KB
• Volume: 35
• Category: Article
• ISSN: 0095-9898
• DOI: 10.1002/jcp.1030350405

✦ Synopsis

THREE FIGURES

Before considering the effects of x-rays on chromosome changes the plant with which we work should be introduced. Trndescuntia is a small perennial plant which is common in the south central states and is commonly known as spiderwort. Some species, when grown in the greenhouse, can be kept in flowering condition throughout the year, and are always available f o r experimental work.

The young pollen grains are used f o r work in radiation cytology. The newly formed microspores contain a single nucleus which remains in the resting stage for 4 o r 5 days or longer during the winter months. During prophase the chromosomcs become split into sister chromatids, and the chromosomes contract by means of coiling of the chromatids. This stage lasts for 30 to 50 hours depending on the conditions of light and temperature. At the end of this period the chromosomes become oriented at metaphase and can be analyzed readily. The 6 chromosomes are relatively large and are of approximately equal size.

When the microspores in the young flower buds are irradiated at the resting stage the chromosomes are slender single threads in the form of loose "relic" spirals. A break in the thread at this stage can "heal" or undergo restitution so that no visible alteration is observed at later stages. If a single break fails to reunite, the chromosome loses part of one arm and is referred to as a rod deletion. Illegitimate unions of broken ends of the chromosomes produce the most frequent