Mapping Mutations in C. elegans - Caenorhabditis Elegans: Molecular Genetics and Development - page 8

males. If this result is observed, then new-1(*) is recessive, autosomal, and
(assuming a single locus is involved) a zygotically provided copy of new-1(+)
is sufficient to confer a wild-type phenotype. However, this result does not
exclude the possibility that a maternally expressed copy of new-1(+) can also
confer a wild-type phenotype, and this will be tested by examining the F2s, as
described below. Note that this result is also consistent with the unlikely possi-
bility of a paternal effect mutation (phenotype usually determined by genotype of
sperm; see Browning and Strome (1996) , Hill et al. (1989) , Seidel et al. (2008) ,
but also Darby et al. (2007) ).
Next, pick a single non-New F1 hermaphrodite onto each of 10 plates, incubate at
20 for 4 days (assuming that New is optimally scorable in adults), and then
inspect the progeny.
i) Zygotic-Effect Mutations.
The most likely result is that 1/4 of the F2 progeny are New. In this case, it is
highly likely that a single gene recessive, zygotic-effect mutation is respon-
sible for the mutant phenotype (i.e., phenotype is determined by the genotype
of zygote). The New progeny will have genotype new-1(*)/new-1(*), and thus
be homozygous for N2 sequences in the vicinity of the new-1 locus. Pick New
and non-New F2s for SNP mapping, as described in Section VI.
ii) Partial Maternal Effect Mutations.
If New F2s are present, but the fraction is less than 1/4, but clearly greater
than 1/16, then it is likely that the new-1(+) allele present in the F1 her-
maphrodite confers partial maternal rescue of the homozygous new-1(*)
progeny. If the fraction of New F2s is 1/16, then it could be that more
than one locus is responsible for the New phenotype and/or that partial
maternal rescue occurs. These possibilities will be resolved by the mapping
data. Regardless of the basis for incomplete penetrance in the F2s, animals
that are New are likely to be homozygous for new-1(*) (or both new-1(*) and
new-2(*) if two loci are involved). Pick New and non-New F2s for SNP
mapping, as described in Section VI.
iii) Recessive X-linked Mutations
The next most likely result is that all of the hermaphrodite progeny are non-
New, but all of the F1 males are New. In this case, new-1 is almost certainly
X-linked. In this case, use the F1 hermaphrodites to proceed with SNP
mapping as for autosomal recessive mutations. Note, this result is also
consistent with the unlikely possibility that new-1(*) is specifically domi-
nant in males. This is rare, but has been observed ( Barton and Kimble, 1990 ;
E.J.L., unpublished), and should be considered if candidate genes on the X
do not satisfy confirmatory tests.
iv) Dominant and Maternal Effect Mutations
If both males and hermaphrodites are present among the F1 progeny, but all
are New, then it is likely that either new-1(*) has a dominant zygotic effect or
new-1(*) has a strict maternal effect (i.e., phenotype of progeny is solely