Mapping Mutations in C. elegans - Caenorhabditis Elegans: Molecular Genetics and Development - page 11

for mutations that are homozygous viable/fertile, apply the criteria in Section III.A.1
prior to proceeding further.

A. Mapping with an Unbalanced Mutation
If no map position has yet been established, set up a cross with 10-15 young adult/
L4 males of strain CB5600 (genotype: ccIs4251[myo-3::GFP] I; him-8(e1489) IV)
and 6-10 hermaphrodite progeny obtained from aworm of genotype new-1(*)/new-1
(+). ccIs4251 is an insertion near the center of chromosome I (map position + 4.0)
that dominantly expresses GFP within body muscle nuclei. CB5600 is available from
the Caenorhabditis Genetic Stock Center. Incubate at 20 for 3 days, then use a
dissecting microscope equipped with GFP optics to inspect the progeny. If GFP(+)
New males are present (and GFP(+) New hermaphrodites are absent), then new-1 is
very likely on the X chromosome. If none of the GFP(+) progeny are New, then clone
12 GFP(+) F1 hermaphrodites and incubate at 20 . After 4 days, inspect the progeny
to identify plates that carry the new mutation. If new is unlinked to ccIs4251, then
75% of the New progeny will be GFP(+).
In parallel to cloning the GFP(+) F1 hermaphrodites, set up a cross with 10-20 F1
males and 5-8 CB4856 hermaphrodites. If new-1 is not found to be linked to
ccIs4251, then clone 24 GFP(+) hermaphrodite progeny. Incubate these at 20 , then
score each plate for the presence of New progeny. Approximately four of these plates
should segregate New offspring. Pick New and non-New progeny for SNP mapping
as in Section VI.

B. Mapping with a Balanced Mutation
The exact procedure to be followed will depend on the properties of the balancer
chromosome. For example, if new-1(*) is being kept across from a balancer chro-
mosome that carries a GFP marker, then one can cross CB4856 males with the
balanced strain and pick non-New non-GFP F1 hermaphrodites. Self these, then pick
New and non-New F2s for SNP analysis as in Section VI.

V. Modifier Mutations

A. Types of Modifiers
A typical modifier screen begins with animals that are homozygous for a
primary mutation, prim-1(*).Theprim-1(*) allele could be dominant, as in the
case of an integrated GFP expression reporter, or recessive, as in the case of a
typical loss-of-function mutation. To perform the screen, prim-1(*) animals are
mutagenized and progeny are then screened in the F1 or subsequent generations
for animals that are Mod, that is, exhibit some modification of the Prim