186 • Alternatives to Animal Use in Research, Testing, and Education 
the gene pool is affected, even if the mutation is 
not expressed in the progeny. The mutations that 
occur in somatic cells that are of greatest concern 
are those that lead to cancer (18). 
Recent advances in the techniques of cell biology 
have led to an increase in the types and sophisti- 
cation of mutagenicity tests available. Mutations 
can be detected by analyzing DNA or its fragments 
or by observing changes in the size, shape, or num- 
ber of the chromosomes (which contain DNA), as 
well as by observing changes in a whole organism 
(34). Mutation can also be detected by measuring 
the amount of DNA repair. 
Micro-organism Tests 
The most commonly used test for mutagenicity 
is the Ames test for “reverse mutation” in Salmo- 
nella typhimurium (3). Mutagenicity is detected 
by exposing an already mutated strain to poten- 
tial mutagens . If the mutation is reversed, the bac- 
teria regain their ability to produce the amino acid 
histidine and will proliferate in a histidine -deficient 
culture medium. 
The Ames test, as well as most other mutagenic- 
ity tests involving micro-organisms, does not avoid 
animal use entirely . To determine whether the meta- 
bolic products of a substance might be mutagenic 
even if the substance itself is not, liver prepara- 
tions from rats or other rodents are used to pro- 
duce at least some of the likely metabolic products . 
Micro-organism systems may fail to detect or may 
overpredict mutagenic changes that could occur 
in whole animals or humans . For example, the sys- 
tem provided for metabolism may not be capable 
of reproducing conditions in vivo, or in the case 
of screening for carcinogenicity, mutation may not 
be the initiating event. On the other hand, such 
systems may indicate mutagenicity when the DNA 
repair system of mammals would reverse the mu- 
tation. 
Other bacterial tests have been developed using 
S. typhimurium , Escherichia coli, and Bacillus sub- 
tilis. These systems do not seem to offer any par- 
ticular advantage over the Ames test, although 
thorough evaluation is hampered by lack of a com- 
parable database of results (28). Tests have also 
been developed for molds (30), fungi (16), and 
yeasts (18,82). 
In Vitro Tests 
In vitro mutagenicity tests may be done with cul- 
tured mamm alian cells that are exposed to toxic 
substances, although many mammalian in vitro 
tests also have an in vivo variant. Such tests typi- 
cally measure acquired resistance or lost resistance 
to the effects of the toxic substance. Most com- 
monly used are a mouse lymphoma cell line or ham- 
ster ovary cells, but almost any well -characterized 
cell can be used. Ovary cells are often used be- 
cause, as germ cells, they have half the number 
of chromosomes to be evaluated (18). 
A test known as the specific locus test can be 
done with Chinese hamster ovary cells They are 
exposed to a test substance and their response to 
the normally lethal 8-azaguanine or 6-thioguanine 
in cell culture determined. The cell's ability to sur- 
vive, requiring the ability to metabolize the 8- 
azaguanine or 6-thioguanine, is an indication of 
the occurrence of mutation as a result of exposure 
to the test substance. This test can also be done 
with mouse lymphoma cells exposed to 5-bromo- 
deoxyuridine or trifluorothymidine (23). 
The sister chromatid exchange test relies on the 
fact that certain substances will cause DNA break- 
age and reunion. This damage can be observed 
by staining the original chromosomes so that any 
segments exchanged during replication can be ob- 
served. Commonly used cells include human lym- 
phocyte cells and rodent and human fibroblasts 
(37). Both the specific locus test and the sister chro- 
matid exchange can also be performed as in vivo 
procedures (see ch. 7). 
Although the cells are usually derived from ani- 
mals, there is a considerable net savings in animal 
lives when in vitro mutagenicity tests are per- 
formed. For example, the rat mast cell assay can 
be used to screen severe irritants, and one rat can 
supply enough tissue to replace the use of 48 ani- 
mals in in-vivo procedures (103). 
Tests Usijig Insects 
The most widely used insect for genetic studies 
is the fruit fly , Drosophila melanogaster (114, 115). 
The fruit fly has well-characterized genetics and 
is similar to mammals in many key reactions. A 
variety of end points can be detected. The most 
common, and probably most sensitive, test is the 
