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MUTANTS AND LINKAGE I N MORMONIELLA
GEORGE B. SAUL
~ N DAND
MARION KAYHART
Dartmoath College, Hanover, New Hampshire and Cedar Crest College, Allentown, Pennsylvania
Received July 27, 1956
HE research of various workers has resulted in the accumulation of a large
number of mutant stocks of Mormoniella vitripennis (WALKER).Some of these
mutants have been described by WHITING(1951); more recently, many others have
arisen spontaneously or as the result of radiation studies conducted by KAYHART
(1956) and SAUL(1955).
Many of the mutants are a t the complex locus which WHITING(1951) has named
the R locus, but mutations a t other loci have also been found. Because of the increasing use of Mormoniella as research material, it is desirable to describe these
mutants, and to summarize their linkage relationships. It would further be desirable
to have available a linkage map corresponding to the five chromosomes of Mormoniella; this study is a contribution toward that goal.
T
MATERIALS AND METHODS
Mormoniella is a chalcidoid Hymenopteron parasitic on the pupae of various
muscoid Diptera. Males are haploid and arise from unfertilized eggs; diploid females
arise from fertilized eggs. Unmated females thus produce only male progeny; the
ratio of phenotypes among these approximates the segregation of genes among the
gametes of the parent females. The blowfly Sarcophaga bullata Parker is used as the
host in the experiments to be reported here. Details of the life cycle of Mormoniella
are described by SAUL(1955).
The wild type wasps have reddish-brown eyes and iridescent bronze-colored
bodies. Females have darker antennae and body color than have the males. The
wings of the females are of normal size; the males are brachypterous.
Most of the mutations obtained to this time affect either eye color or body color.
The mutant eye colors vary from black through deep red, orange-red, orange and
light peach, to oyster-white. In general, double mutants are in color as light as or
lighter than either single mutant type. Body colors include purple, various bluegreen shades, and deep blue. A lavender body color mutant was obtained, but it was
lost before it could be tested for linkage. Mutants are kept as pure stocks unless they
are female-sterile, in which case heterozygous females are crossed with mutant males.
All of the mutants are recessive to wild type.
In this study, standard conventions are followed in designating the mutants and
previously published names of mutants are retained. Eye color mutants for which a
name has not been published are named, when possible, by reference to colored plates
in A Dictionary of Color (MAERZand PAUL1950). The number of the plate which
corresponds most closely to the eye color is used in the description of the mutant,
and where possible the name attached to the plate is used for the mutant. Other
mutants, such as body color mutants, which can not be named by this method, are
named arbitrarily.
MUTANTS A M ) LINKAGE I N MORMONIELLA
93 1
The apparatus used for comparing eye colors with the Maerz-Paul color charts
was designed by DR. SARAH
FLEMISTER.
The wasp is observed by reflected light under
the low-power objective and 1OX ocular of a compound microscope. It is placed on
its side, with the surface of the eye in full view. The color charts are covered with a
piece of black cardboard which has an opening in the center; this opening permits
comparison of the eye color with one tab at a time. A spotlight illuminates the eye
and a second spotlight illuminates the color chart, which can be observed by shifting
one's view only slightly from the microscope. All observations were made on freshly
eclosed males.
Linkage tests were made by two factor crosses. I n general, five males of one mutant
type were crossed with five females homozygous for a second mutant gene. Five
F1 females from the cross were set unmated and the Fz progeny, all male, were
counted. Linkage, when present, was shown by reductions in the numbers of wasps
in the recombinant classes (wild type and, in the absence of epistasis, double mutants).
If both mutants to be crossed were female sterile, PI females heterozygous for one
of the mutant types were used. Each F1 female was set individually and only those
Fz cultures which contained both mutant types were used for linkage counts. These
cultures would be expected to include about half of the total number set.
If a cross indicated that two traits were linked, then, when possible, five males of
the double-mutant type were crossed with five homozygous wild type females and
the cross was carried to the FZgeneration as described above. In these cases linkage
was thus estimated from crosses in the coupling and in the repulsion phases.
When possible, the calculation of linkage followed the geometric mean averaging
system given by FISHER
in The Design of Experiments (1949). The gametic ratio
r / s is given by:
In this formula, a1 and a2 are the total recombinants from the coupling and repulsion
experiments respectively; bl and bz are the total parentals from these crosses. This
method compensates for differences in viability of the classes, but does not compensate for linked lethals.
In the case of epistasis, linkage was estimated from the cross in repulsion phase
by dividing the number of wild type wasps (m) by the total number of wasps in the
wild type class and the class ( n ) showing the hypostatic trait. The formula is thus
m / ( m n ) . The formula n/(m n) gives an estimate of linkage from the cross
in the coupling phase. Since the double mutants could not be selected with certainty, several crosses were made for the coupling experiment. Each mating involved
a single male from the class showing the epistatic trait and a wild type female; only
Fz cultures which included wasps showing the hypostatic trait (and which thus were
sired by double-mutant males) were used for linkage counts. The geometric mean
averaging system employed for more precise measurement of linkage can, in this
case, use only one class of parentals and one of recombinants from each cross, since
the other classes are identical due to the epistasis. In the general formula given above,
+
+
932
GEORGE B. SAUL ~ N D
AND MARION KAYHART
al, a2 ,bl , and bz represent only the distinguishable parental and recombinant classes;
the method thus becomes the same as that proposed by MULLER(1916).
In Fz cultures from some crosses, only wild type and one class including both the
single-mutant and the double-mutant types could be distinguished. In these cases,
linkage was measured by doubling the number in the wild type class and dividing it
by the total count in the culture.
MUTANTS
The following list is a brief summary of information about 22 mutant types of
Mormoniella. Apparent isoalleles are not included, nor are mutations that were lost
before they could be tested and characterized adequately. Important information
about the factors scarlet-DR, tomato, garnet, and purple has been reported by
WHITING(1951) ; these factors are therefore listed here with only the Maerz-Paul
references (where applicable) and literature citations. Of the numerous alleles a t the
complex eye color locus R, only those used in linkage tests are listed. The following
information is given for all mutants except those mentioned above: symbol, name,
investigator who found the mutant, date found, inducing agent (if any), description
and important characteristics, and Maerz-Paul reference (if applicable). The MaerzPaul reference includes the plate and tab numbers.
bk: black. GROESBECK1952. Induced by X-rays. Eyes black, body slightly greener
than wild type. Interacts with dark red eye colors to give lavender or light peach
and with scarlets and lighter colors to give white. 48:L-12.
bl: blue. KAYHART
1953. Spontaneous in wild type stock. Body dark blue. Female
sterile. Viability considerably lower than wild type.
ga: garnet. 3:L-11. (WHITING1951).
g@8t-b:garnet-scarlet-b. KAYHART
1953. Induced by fast neutrons. Eyes orange-red,
phenotype identical to R s t - D R 2 :L-11.
gZ: glass. MILROOD
1952. Spontaneous. Eyes narrow, facets poorly differentiated and
reduced in number. Female almost sterile. Viability somewhat lower than wild
type.
gr: green. KAYHART
1953. Induced by slow neutrons. Body grass-green. Female
sterile, viability somewhat lower than wild type.
gb : green-blue. WHITING1952. Spontaneous from wild type. Body greenish-blue to
deep blue. Female sterile.
or: orange. SAUL1952. Induced by X-rays. Eye color dull orange. 2:D-12.
pZ: pellucid. WHITING1952. Spontaneous from +/ti-277. Eye color oyster-white,
phenotype identical to R o U - D R . Epistatic to all other eye colors. 4:A-7.
pu: purple. (WHITING
1951).
rh: reddish. KAYHART
1953. Induced by slow neutrons. Eye color dark rust-red.
6: 1-11.
R 8 t - 4 - D R : Scarlet-DR.2 :L-11. (WHITING
1951).
scarlet 426. GROESBECK1952. Induced by X-rays. Phenotypically identical
to scarlet-DR.2 :L-11.
st-c: scarlet-c. WHITING1953. Spontaneous from wild type. Phenotypically identical
to scarlet-DR.2:L-11.
933
MUTANTS AND LINKAGE I N MORMONIELLA
TABLE 1
Itdependent assortment of traits in Mormoniella, including data from representative two-factor crosses.
Genes are listed alphabetically; crosses of each gene, in order, with succeeding genes are grouped together. A dash in the list of FZ classes from a cross indicates that the class i s included with another
class identical or epistatic to it. The symbol a/b means that the FI female is heterozygous for factors
crossed in repulsion phase; ab/+ indicates factors crossed in coupling
Fz males
FIfemale from cross
a X b or ab X
+
+
72
41
98
40
76
49
71
69
54
68
114
72
71
95
65
80
38
60
56
118
103
84
99
40
109
96
96
69
100
157
44
51
35
78
77
54
60
133
75
62
100
45
a
87
39
99
61
79
53
75
61
60
118
103
63
84
93
56
50
32
66
56
90
78
80
103
38
95
94
95
80
87
138
44
53
31
66
73
78
62
111
66
59
92
47
b
58
29
83
39
79
119
77
58
62
72
107
74
73
65
59
37
81
45
104
85
78
76
97
212
110
97
74
ab (with phenotype)
56
13 pale red
66
57
95 oyster
62 deep gentian
56 oyster
57 oyster
81 oyster
124 pale red
55 dark red
85
61
65
30
70
46
63
99
79 oyster
90 scarlet
87 oyster
73 oyster
72 scarlet
39
55
31
97
73
54
59
32
55
24
60
51
61
4:
58
57
75
52
78
57
97
44
934
GEORGE B. SAUL 2ND AND MARION KAYHART
TABLE l.-Contimed
FI female from cross
a X b or ab X
+
A males
+
75
60
472
63
105
42
109
53
59
117
78
92
86
56
65
178
86
53
94
217
154
76
93
so
87
135
109
69
76
167
56
109
106
67
85
138
a
68
61
408
67
107
38
90
120
119
99
120
137
187
155
173
166
83
54
124
196
157
224
283
81
96
124
307
76
73
149
70
79
114
70
98
133
b
78
73
154
88
45
84
59
85
89
85
70
64
86
56
109
353
86
72
ab (with phenotype)
54
69
60 oyster
54 oyster
70 light peach
29 white
-
-
81 orange
54 orange
122 orange
-
-
96 light peach
70 orange
56
72
79 oyster
77 orange
73
71
61 light peach
73 orange
67
43 oyster
st-d: scarlet-d. KAYHART
1953. Induced by slow neutrons. Phenotypically identical
to scarlet-DR.2:L-11.
tl: tile. KAYHART
1953. Induced by X-rays. Eye rust-red. 3:D-12.
t b g - b : tile-oyster-b.,WHITING1954. Spontaneous from wild type. Eye color oysterwhite; phenotypically identical to pl and epistatic to all other eye colors. Complementary to tl. 4: A-7.
to: tomato. 4:F-12. (WHITING1951).
tota tomato-tanagra. SAUL1952. Induced by X-rays. Dark red eye color approaches
wild type with increasing age. Female sterile. Viability low. 7 :J-9.
935
MUTANTS AND LINKAGE I N MORMONIELLA
tomato-manzanita. WHITING1953. Spontaneous from wild type. Eye color
dark red, slightly browner than tota in color. 7:L-10.
tomo: tomato-moroccan. KAYHART
1953. Induced by slow neutrons. Eye color dark
red, but lighter than tota. 5:K-11.
tomato-moroccan-2. KAYHART
1953. Induced by slow neutrons. Eye color
overlaps tomDin adults but is slightly lighter in pupae.
Wild type: 8:H-8.
tomz:
RESULTS O F LINKAGE TESTS
As shown in the preceding list, 15 loci are now recognized in Mormoniella. Mutants
a t 14 of these have been tested for linkage; gr has not been tested due to difficulties
in establishing it in stock. For similar reasons bl has not been crossed with genes a t all
known loci. Table 1 gives results of tests which show no linkage; Table 2 gives results
of tests which indicate that the genes crossed are linked. In the left-hand columns of
the tables are genotypes of FI females from the crosses of each gene with each succeeding gene: a/b means that the female is heterozygous for a and b and that the
cross was in repulsion, whereas ab/+ means that the cross was made in coupling.
The four columns of Fzmales are arranged to show the wild type (+), mutant type a,
mutant type b, and the double mutant ab. Phenotypes of double eye color mutants are
given when distinct from either single mutant type.
I n most cases, only one mutant a t a locus was used to test the locus for linkage.
This mutant was selected on the basis of high viability and a phenotype easily distinguished from wild type and (if possible) from other mutants used in the crosses. A
few additional crosses, not included in the tables, indicated that linkage values were
unchanged when other alleles a t linked loci were crossed; the one exception to this
(alleles a t the Ga locus) is reported and discussed below.
TABLE 2
Linkage of traits in Mormoniella. See legend of table I for explanation of organization of table
FI female from cross
a X b orab X
+
bl/gb
ga/tl
ga tl/+
ga*t--b/tl
gaa$-btl/+
gl/Ra'-DR
gb/rd
gb/tomz
gb tomz/+
or/st-c
or st-c/+
pllst-d
pl st-d/+
rd/tomr
rd tomr/+
F2 males
!
+
51
106
124
21
160
4
28
84
190
21
200
65
97
15
220
a
321
20
155
17
247
165
240
50
290
7
317
110
-
b
244
357
22
172
22
230
158
200
42
2 78
4
261
20
547
9
ab (with phenotype)
88 oyster
95 oyster
17 light peach
182 light peach
8
41
84
149
14 light peach
159 light peach
-
5 light peach
122 light peach
936
GEORGE B. SAUL
2ND
AND MARION KAYHART
The data in the tables indicate that there are five groups of linked factors and a
single locus (Bk) not included in any of the linkage groups. When linkage is calculated
as described above, the groups are as follows:
1. R
Pu
10.6
1-24.-1
2.
To
GI
Rd
3.1
1-24.4-----1
Gb
17.6
BI
34.6
or
3. st-c
4.2
St-d
4. PI
18.5
5 . TI
Ga
(19.0 or 10.3)
6 . Bk
Distances are in Morgan Units. Rd and B1, and To and B1 recombined a t random. The
R-Pu linkage was calculated from the data of WHITING(1950).
If ga is crossed with tl, 19.0% recombination is observed; if
is used in the
cross, 10.3% recombination results. These percentages of recombination are almost
unchanged if other alleles a t the TI locus are used in the crosses. It is therefore possible that the gaat-bstock contains a crossover suppressor linked with the Ga locus.
The cross of tlou-b with tl gives wild type F1 females; these females, unmated, produce only tlo’-b and tl Fz males. It is possible that tlou-b and tl are a t separate, completely linked loci. I t is also possible that they are at one complex locus and show the
complementary allelism that has been described for the R locus. This second possibility is the basis of the nomenclature adopted here.
The factor for purple body color shows about 10.6% recombination with the R
locus if the wild type allele for glass eye is present. When gl is present, the R-Pu recombinations drop to about 2.1 % (19 in a culture of 897). The R locus and glass show
about 2.4% recombination; recombinations between gl and pu occur in less than 1%
of the possible cases. It is suggested by DR. P. W. WHITING(1955) that “gl” may be
an inversion, and that the Pu locus may be included within the inversion. Cytological
observations on gl/+ females have not yet been made. The viability of gl males is
about equal to that of
males, and SI/+ females have high fecundity. The fecundity
of homozygous gl females is very low, however.
Spermatogonial cells of Mormoniella contain five chromosomes, the haploid number for the species. Although this study has shown the existence of five linkage groups
and one factor, black, segregating independently of all other loci, it is impossible to
determine a t present whether the five linkage groups are located on five separate
chromosomes.
+
MUTANTS AND LINKAGE IN MORMONIELLA
937
SUMMARY
1. New mutants in Mormoniella are described and discussed. A system for describing and naming eye color mutants is introduced; this system is based on the use
of Maerz-Paul color charts.
2. The known loci are shown to be associated in five linkage groups as shown on
page 936.
3. Data obtained by the use of gl stock are discussed. These data support a suggestion by WHITINGthat “glass” is an inversion which may include the Purple locus.
4. It is possible that the Tile locus is complex, containing factors which show
complementary allelism.
ACKNOWLEDGMENTS
Much of this study was completed while the authors were graduate students a t the
University of Pennsylvania. During this period the work was supported by the
National Institutes of Health (G. B. S., predoctoral fellowship) and the Atomic
Energy Commission (M. K., assisting DR. P. W. WHITINGunder contract AT(30-1)-1471 of the University of Pennsylvania with the U. S. Atomic Energy Commission).
LITERATURE CITED
FISHER,
R. A., 1949 The Design of Experiments. New York: Hafner Publishing Company, Inc.
5th ed., pp. 221-225.
KAYHART,M., 1956 A comparative study of dose-action curves for visible eye-color mutations
induced by X-rays, thermal neutrons, and fast neutrons in Mormoniella vitripmnis. Radiation
Res. 4: 65-76.
1950 A Dictionary ojColor. New York: McGraw Hill Book Company,
MAERZ,A., and M. R . PAUL,
Inc., 2nd ed.
MULLER,H. J., 1916 The mechanism of crossing over. Am. Naturalist 60: 352-354.
SAUL,G. B. ~ N D ,1955 The induction by X-rays of recessive lethals in the mature sperm of Mormoniella vitripennis (Walker). Radiation Res. 2: 447460.
WHITING,P. W., 1950 Linkage in Mormoniella. Genetics 36: 699. (Abstract)
1951 Multiple complementary alleles in Habrobracon and Mormoniella. J. Genetics 60: 206214.
1954 Comparable mutant eye colors in Mormoniella and Pachycrepoideus (Hymenoptera:
Pteromalidae). Evolution 8: 135-147.
1955 Linkage relations of purple, glass, and the eye-color locus R in Mormoniella. Genetics 40:
602. (Abstract)
WHITING,P. W., and L. H. BENKERT,1934 Azygotic ratios in Habrobracon. Genetics 19: 237-267.