MUTATIONS

A variant exists when there are two or more
alternative phenotypes.
Usually, one is designated as normal or wild-type
because it is the phenotype characteristic of
wild-type flies; the other or others are considered
mutant alternatives because they represent
departures from normal.  Distinction between normal
and mutant may become blurred or disappear where
both alternatives are characteristic of wild-type
strains, as in isoalleles.  The pair or group of
alternatives defines a locus, which is given a name
that suggests the main diagnostic features of the
mutant form of the locus without regard to secondary
characters.  The name is concise and is preferably a
simple adjective such as black or a noun such as
Bar.  When the main character is recognized in the
heterozygote, the mutant is considered dominant and
its name begins with an upper-case letter; when it
is recognized in the homozygote, the mutant is
considered recessive and its name begins with a
lower-case letter.

For convenience, a symbol is assigned to each mutant
type.  This symbol is an abbreviation of the name
that uniquely designates the mutant in question; it
combines brevity with information.  It usually
begins with the same letter as the name, is always
italicized, and never contains Greek letters,
subscripts, or spaces; e.g., r for
rudimentary, R for Roughened, ro for
rough, rs for rose, and ry for rosy.  In
designations of genotypes with several mutant genes,
symbols of genes on the same chromosome are
separated by spaces (e.g., y w f B); symbols
of genes on homologous chromosomes are separated by
a slash bar (e.g., y w f/B); symbols of
genes on nonhomologous chromosomes are separated by
semicolons and spaces (e.g., bw; e; ey).
Names are not italicized in text.

MULTIPLE ALLELES

The alternatives or
alleles at a particular genetic locus are designated
by the same name and symbol and are differentiated
by distinguishing superscripts.  At publication of
the original volume, heterozygotes for allelic
mutants were thought always to show a mutant
phenotype and segregation of the mutants at meiosis.
Since that time, however, discoveries of
complementation and intra-allelic recombination have
revealed the widespread existence of complex
pseudoallelic series, with consequent complications
in the definition of allelism.  By the criteria that
they occupy virtually identical positions on the
genetic map and have similar phenotypic effects,
mutants formerly thought to be at different loci
may now be considered changes in the same
pseudoallelic complex; e.g., fa and spl,
lz and amx, and m and dy.
The locus will probably be defined ultimately as the
unit of transcription or, more likely, of
translation; but in the current state of knowledge,
we have been content to adhere to the historic
terminology.  One school of thought names every
recombinationally separable element; another gives
all members of the same complex a single name with
arbitrary superscripts.  The latter is our
preference.

The superscript notation desginating alleles has a
number of different forms.  A common device is an
abbreviation that further characterizes the
particular allele or that was used as the locus
symbol before allelism was established.  This
practice is avoided because it has the disadvantage
of preempting useful symbols and names from use as
locus designations.  Another unacceptable device is
the use, as superscripts, of elements of the
genotype in which the allele arose, since such a
designation implies something more than a trivial
connection between allele and element.
More-acceptable superscripts for allelic
designations are arbitrary numbers, experiment
numbers, capitalized initials of the finder or
laboratory, or the date of discovery.  The numeral\ 1
is the implied superscript of nonsuperscripted
symbols.  Whereas genes in their same allelic series
are designated by the same symbol but with different
superscripts, mutants with similar phenotypes at
different loci are not given the same symbol and
differentiated only by a superscript; this was done
extensively in the past; for example, for genes
causing formation of melanotic pseudotumors.

For a recessive allele of preponderantly dominant
series or a dominant allele of a predominantly
recessive series, the superscripts used are r
and D, respectively; e.g., Hn\[r],
Hn\[r2], and bw\[D].  Finally, for the normal
allele in a series, a superscript plus sign may be
used; e.g., b\[+] or B\[+].  The plus symbol
alone implies the normal (wild-type) allele in any
context, such as y/+ or y m f/+.
Absence of a particular locus may be noted by use of
a superscript minus sign with the symbol; e.g.,
bb\[-].

Loci controlling electrophoretic mobility of enzymes
and other proteins require special conventions.
Since electrophoretic variants can be scored equally
well in heterozygotes and homozygotes, the genes
controlling them are considered dominant; e.g.,
Adh.  Alleles specifying the variants are
differentiated by arbitrary superscripts; e.g.,
Adh\[F], Adh\[D], and those specifying the
absence of a particular enzyme or other protein
by an appropriate superscript, such as n
(negative), a zero, or a minus sign, rather than by
a lower-case symbol; e.g., Adh\[n1].  The sole
exceptions to the rule that the genetic determinants
of electrophoretic protein variants be symbolized as
dominant genes are loci originally recognized by
recessive phenotypes and so named; e.g., v and
ry.  For proteins with undetermined activity,
we use the symbol Pt- followed by an arbitrary
designation specifying the particular protein; e.g.,
Pt-1.  Abbreviations for the protein and the
gene are frequently identical, and both are used in
most discussions.  The gene symbol may be
differentiated from the protein symbol by having
only its initial letter capitalized and by being
italicized, whereas the protein symbol is in roman
capitals; e.g., ADH.

In several instances where two members of the same
allelic series were formerly given different locus
names, both are here included under one name; e.g.,
Pm\ =\ bw\[V1].  In other cases, we assume
allelism of mutants with similar phenotypes and
genetic positions even though they have not been
tested for phenotypic interaction.  In such
instances, the basis for the assumption is usually
noted.  Since the practice has not been consistent,
some alleles may be described as different genes.
We make special effort to infer allelism for Minute
loci and for factors causing production of melanotic
pseudotumors.  Bridges and Brehme made few such
inferences.  Except in special cases, investigation
of allelic interaction of sex-linked recessive
lethals is not possible; consequently, they are
often given distinctive symbols where allelism may
actually exist.

MIMICS.  Mutants at different loci
sometimes have similar phenotypic effects.  Such
loci may be handled in several ways.  The simplest
is to give each a distinctive name (e.g., vermilion,
cinnabar, scarlet, karmoisin, cardinal); this method
has the effect of scattering such mimics throughout
the alphabetical listing.  Or a common symbol
separated by a hyphen from a distinguishing symbol
may be used (e.g., tu-1a, tu-1b, tu-2 for
genes controlling production of melanotic
pseudotumors).  Distinctive suffixes are also useful
(e.g., rough, roughoid, roughish, roughex; plexus,
Plexate; dachs, dachsous; maroon, maroonlike).  The
latter two schemes frequently have the virtue of
placing like phenotypes in sequence in an
alphabetical listing.  Some phenotypes result from
mutation at many loci in all chromosomes; these are
given a common symbol followed by a parenthetical
designation of the chromosome and then by a
distinguishing designation.  Examples of this type
of mutant are the female steriles, the lethals, the
Minutes, and the male steriles [e.g., fs(2)B,
l(1)J1, M(1)n, ms(2)E4, respectively].
Conventions for formulating distinguishing symbols
are similar to those for superscripts; use of
information about the cytological or genetic
location is avoided to allow updating such
information without changing the symbol.

MODIFIERS.  The primary effect of some
mutants is to cause another mutant to exhibit a
more-extreme departure from normal (enhancer) or a
more nearly normal phenotype (suppresssor).  Such
mutants are symbolized e or E and
su or Su, followed in parentheses by the
gene modified.  Designation of the particular allele
modified appears as a superscript within the
parentheses and alleles of the modifier gene as
superscripts outside the parentheses; e.g.,
su(lz\[34]) and su(Hw)\[2].  Terms such as
dilutor, exaggerator, inhibitor, intensifier, and
modifier were also formerly used, but we have
usually attempted to classify such genes as
enhancers or suppressors.

FORMAT.  Mutants with their
descriptions are now listed alphabetically
according to symbol and cross-indexed according to
name.  Current terminology is listed in bold face.
All cases of synonymy are also listed in body type
with cross-references to current usage.  Mutants no
longer existing in published stock lists or in
private stock lists that we have examined are
considered lost and are preceded in the list by a
star.  Each mutant is described according to the
following format:

symbol:  name

location:  The location is indicated by the
chromosome number, separated by a hyphen from the
genetic position on the chromosome.  Two levels of
accuracy of the genetic location are indicated,
those carried to tenths of a unit being the more
accurately determined; e.g., 3.0 represents a more
accurate location than 3.  Map units are not
computed to the second decimal place.  Accuracy of a
map position determination is of course dependent on
the accuracy of the positions assigned to the
reference markers; i.e., on the accuracy of the map.
We treat the map as a rough guide to the relative
positions of loci but, considered on a refined
level, it may be inaccurate with respect to both
position and order of genes.  (We have abandoned the
\(+- used by Bridges and Brehme to indicate a
particularly low level of reliability.)

origin:  For induced mutants, the agent is
given; mutants recovered from untreated parents or a
wild population are listed as spontaneous.
Isoallelic variants found as major components of
stocks or populations are listed as naturally
occurring alleles.  The stock or chromosome in which
each mutant arose was listed by Bridges and Brehme;
unless the new mutant is virtually inseparable from
some element of the stock of origin (e.g.,
y\[31d] in In(1)sc\[8]), we omit mention
of the original stock.

discoverer:  Name, date of discovery.

synonym:  Alternative symbol of name or both,
mostly obsolete terminology.

references:  Sources of the major
descriptive material are listed, but bibliographic material may
also appear in some of the other categories.

phenotype:  The most important departures from
normal, which are usually those suggested by the
name, are described first.  Other information about
the phenotype follows, and finally there may be data
on viability and fertility.  The last item in the
phenotypic description is the rank, abbreviated RK.
Mutants are classified into three different ranks
according to their utility in experiments in which
counts are made:  RK1 mutants are easily scored; RK2
mutants are usable but less convenient; RK3 mutants
have limited usefulness.  An RK3 mutant may be one
with good expression and viability but simply not
convenient to use in counting experiments; e.g.,
enzyme polymorphisms.  The letter\ A follows the
rank of mutants associated with chromosome
aberrations.

other information:  This category contains
miscellaneous information that does not fit into one
of the other categories.