include all forms of ionizing radiation. The ICRP leaves the establishment of detailed
technical recommendations to national organizations.
b. International Commission on Radiological Units and Measurements (ICRUM).
The ICRUM (formed in 1925) works closely with the ICRP. The ICRUM develops
internationally acceptable units of radiation and radioactivity and recommends
procedures for their application. Physical data required for the application of radiation
units are developed and reported by the ICRUM.
c. International Atomic Energy Agency (IAEA). The IAEA (organized in 1956) is
a specialized agency of the United Nations. The objective of the IAEA is to promote
peaceful uses of atomic energy. Recipients of IAEA assistance are required to observe
health and safety measures prescribed by the Agency.
d. National Council on Radiation Protection and Measurements (NCRPM).
Founded in 1929, the NCRPM is a group of scientists and other technical experts
concerned with radiation protection. As a national organization, the NCRPM adopts the
basic radiation protection philosophy of the ICRP to the needs of the United States.
The NCRPM publishes its recommendations in a series of reports. The reports have
found wide application in the formulation of Federal radiation protection regulations.
2-12. GENETIC EFFECTS OF RADIATION
a. A gene is a specific sequence of DNA, which specifies the information
required for the cell to construct a specific protein. Traits such as hair color, eye color,
stature, and handedness are familiar displays of specific genes--some known, some
unknown. The alteration of a single base of the DNA sequence can be enough change
to affect an observable trait. Familiar examples of diseases involving single gene traits
are Tay-Sachs disease, cystic fibrosis, thalassemia, and, as a special example, sickle-
cell anemia, involving only a single base change.
b. For single gene defects to be expressed in the first generation, the trait must
be dominantly expressed. To date, some 500 to 900 characteristics are thought to be
dominantly expressed in the human. Extra digits, dwarfism, and some forms of anemia
are examples. Most genes, however, are present in two copies, the proper functioning
of either being sufficient for normal needs. In this case, the trait is said to be recessive
and several generations are required in order to see the change. Tay-Sachs disease is
a well-known example of this category of traits. A third category of gene effects, six-
linked recessive mutations, are a special case of the category of recessive traits in that
the defect is found on the X chromosome. Females, having two copies of the X
chromosome, do not express the single recessive gene; however, males may inherit
and express these conditions. Familiar examples are hemophilia and color blindness.
c. An exposure to ionizing radiation creates mutations or gene changes in all of
the categories listed above. New mutations or traits are not seen, but rather increases
are observed in the known mutable traits. All together, approximately one percent of all