American scientist and cytogeneticist
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- If chromosomes are broken by various means, the broken ends appear to be adhesive and tend to fuse with one another 2-by-2. This has been abundantly illustrated in the studies of chromosomal aberrations induced by X-ray treatment. It also occurs after mechanical rupture of ring-shaped chromosomes during somatic mitoses in maize and is assumed to occur during the normal process of crossing-over.
- (March 1941)"The stability of broken ends of chromosomes in Zea mays". Genetics 26 (2): 234–282.
- When, through radiation or other causes, chromosomes are broken within a single nucleus, 2-by-2 fusions may occur between the broken ends. These fusions may lead to rearrangements of parts of the chromatin complement, giving rise to various chromosomal aberrations which are detected as reciprocal translocations, inversions, deficiencies, etc. Since, in the well-investigated cases, the breakages occurred within a single nucleus, the conditions that lead to fusions of broken ends could not easily be ascertained.
- (November 1942)"The Fusion of Broken Ends of Chromosomes Following Nuclear Fusion". Proc Natl Acad Sci U S A 28 (11): 458–463. DOI:10.1073/pnas.28.11.458.
- An experiment conducted in the mid-nineteen forties prepared me to expect unusual responses of a genome to challenges for which the genome is unprepared to meet in an orderly, programmed manner. In most known instances of this kind, the types of response were not predictable in advance of initial observations of them. It was necessary to subject the genome repeatedly to the same challenge in order to observe and appreciate the nature of the changes it induces. Familiar examples of this are the production of mutation by X-rays and by some mutagenic agents. In contrast to such “shocks” for which the genome is unprepared, are those a genome must face repeatedly, and for which it is prepared to respond in a programmed manner. Examples are the “heat shock” responses in eukaryotic organisms, and the “SOS” responses in bacteria. Each of these initiates a highly programmed sequence of events within the cell that serves to cushion the effects of the shock. Some sensing mechanism must be present in these instances to alert the cell to imminent danger, and to set in motion the orderly sequence of events that will mitigate this danger. The responses of genomes to unanticipated challenges are not so precisely programmed. Nevertheless, these are sensed, and the genome responds in a descernible but initially unforeseen manner.
- The Significance of Responses of the Genome to Challenge, Nobel Prize lecture. nobelprize.org (8 December 1983).
Quotes about McClintockEdit
- In 1950, Barbara McClintock published a Classic PNAS article, “The origin and behavior of mutable loci in maize,” which summarized the evidence leading to her discovery of transposition. The article described a number of genome alterations revealed through her studies of the Dissociation locus, the first mobile genetic element she identified. McClintock described the suite of nuclear events, including transposon activation and various chromosome aberrations and rearrangements, that unfolded in the wake of genetic crosses that brought together two broken chromosomes 9. McClintock left future generations with the challenge of understanding how genomes respond to genetic and environmental stresses by mounting adaptive responses that frequently include genome restructuring.
- In the year of her election to the National Academy, she began the series of experiments that led her to transposition—work that many now see as the most important of her career. At the time, only she thought so. To most, her conclusions seemed too radical.