(dP? 14. JH 192 dpo + L bw. 2. 0.54. 1013. 1.68. 15. JH 192. dpO cn L bw. 3. 0.56. 1072. 0.84. 16. JH 192. dPov + + +. 1. 0 53. 479. 1.87. 17. JH 192 dpo cn L +.
THE LOCATION O F A MUTATOR FACTOR IN A STRAIN OF DROSOPHZLA MELANOGASTER BY ASSAYING MALE RECOMBINATION1 NITA N. SCOBIEz AND HENRY E. SCHAFFER Department of Genetics, North Carolina State University, Raleigh, NC 27650 Manuscript received October 15, 1980 Revised copy accepted March 25, 1982 ABSTRACT
In a set of “mutation accumulation lines,” of Drosophila melanogaster that had originated from two different wild-caught lethal-carrying second 1977; chromosomes (YAMAGUCHI and MUKAI1974; MUKAIand COCKERHAM VOELKER, SCHAFFER and MUKAI1980) a correlation exists between high rates of reverse mutation at two visible loci and the ability to induce male recombination (SCOBIEand SCHAFFER1982). The second and third chromosomes were extracted from the lines demonstrating these phenomena and tested for independent ability to induce male recombination. When the wild chromosome being tested was of male origin, extracted second chromosome lines were found to induce moderate to high levels of male recombination and reduced transmission frequency of the wild chromosome (the k value). The recombinants recovered in these crosses also demonstrated a high level of double-crossover recombination without the recovery of the reciprocal doublerecombinant types. In addition, identifiable portions of extracted second chromosomes of male origin have been placed on very similar, marked genetic backgrounds and tested for their ability to induce male recombination. Results of this procedure have identified two regions of the second chromosome that induce male recombination and reduce k values. These results are consistent with the hypothesis that there exist two mutator factors on the second chromosome, each associated with a “mutation accumulation line” with an unstable locus. N
analysis of a set of 1,000 mutation accumulation lines of
D.melanogaster
A originating from two wild lethal-carrying second chromosomes was reported
by YAMAGUCHI and MUKAI(1974). Based upon their cytological observations they postulated the presence of a mutator factor. As a result of the manner in which the lines had been constructed they eliminated the possibility that the factor was cytoplasmic and stated that it was located on either Chromosome ZZ, or, with less likelihood, on Chromosome 111. Paper NO. 6548 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina. This investigation was supported in part by Public Health Service Research Grant No. GM 11546 from the National Institute of General Medical Sciences. The first author was recipient of a Public Health Service Foreign Postdoctoral Fellowship during final preparation of the manuscript. Present address: Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, North Carolina 27709. Genetics 101 : 40541G July/August, 1982
406
N. N. SCOBIE AND H. E. SCHAFFER
I n an accompanying paper, SCOBIEand SCHAFFER(1982) describe the identification of a mutator factor in the same set of “mutation accumulation lines.” The presence of the mutator factor was substantiated following the identification of several lines in which genetic instability was shown to exist at either of two second chromosome loci from the MULLER“12ple” stock (the dumpy locus or the vestigial locus). The instability was demonstrated by the occurrence of high rates of reversion at these loci and by the ability of males from these lines to induce male recombination in a subsequent generation. The present study was undertaken to identify the chromosome upon which the mutator factor was carried and to determine the region(s) of the chromosome in which the factor(s) was located. MATERIALS A N D METHODS
Stocks: JH 184 - SMI(Cy)/l(JH)dp””; J H 192 - SMI(Cy)/l(JH)dpOl;J H 235 - SMI (CY)/ l ( J H )ug.
JH 184, JH 192 and JH 235 are mutation accumulation lines, selected from a group of 500 lines of identical origin for second chromosome visible mutations and high rates of reversion. Extracted second and third chromosomes from these stocks are used to demonstrate male recombination. Extracted second chromosomes are used for mapping. al b c s p : a standard second chromosome line with four recessive markers, a1 (aristaless, 2L-0.01), b (black body color, 2L-48.0), c (curved wing, 2R-75.5), sp (speck, 2R-107.0); used to identify the products of male recombination. dpour cn L bw: dpov’ (dumpy wing and thoracic vortices-synthesized by Ives, 2L-13.0), cn (cinnabar eye color, 2R-57.5), L (lobed eye shape, acts as a recessive, 2R-72.0), bw (brown eye color, ZR-104.5)-synthesized a t N.C. State University; used to multiply mark the extracted second chromosome for mapping. S M I , Cy/Sco; TM6, Ubx/Sb: Sco (Scutoid; no bristles on the scutellum, dominant expression, recessive lethal, 2L-51.0), Sb (Stubble; stubble bristles, dominant expression, recessive lethal, 3&58.2), Ubx (Ultrabithorax; halteres of heterozygote about twice normal volume, homozygous lethal, 38-58.8) ; used to extract second and third chromosomes from lines J H 184, JH 192 and JH 235. and GRELL(1967). A complete description of all marker stocks in available in LINDSLEY All marker stocks originated from the mid-American Drosophila Stock Center, Bowling Green, Ohio. All crosses were made using standard cornmeal media and were maintained at a temperature of 2 5 f l ” . Extraction of Chromosomes I1 and 111: Chromosomes ZZ and 111 were extracted from three lines in which mutations had been identified, and i n which high rates of back mutation and a n ability to induce male recombination were observed subsequently ( SCOBIEand SCHAFFER 1982). The lines used were JH 184 which carried the mutant dpou at the d p locus, JH 192 which carried dpoz at the d p locus, and JH 235 with ug at the ug locus. From these lines the second and third chromosomes were extracted and placed on extremely similar genetic backgrounds. Figure 1 outlines the process that resulted in the formation of stocks carrying either the second or the third chromosome from the mutation accumulation lines in a genetic background with dominantly marked second and third chromosome balancer chromosomes. Male recombination in extracted chromosomes: The method used for testing the ability of the extracted chromosomes to induce male recombination is shown in Figure 2 and is identical to that used when the lines were first tested for this ability (SCOBIEand SCHAFFER 1982). Males and females containing only the second or third extracted chromosome in a different and consistent genetic background and cytoplasm (excepting only the Y and the small fourth chromosome) were mated in mass culture to a marked second chromosome tester stock in generation 4. Individual male progeny of the appropriate genotype, as indicated in generation
40 7
LOCATION O F MUTATOR FACTOR BY M R
gen2:
X;
:.
''0
SM1,Cy
.x
Sb
.
TM6,Ubx
x -,x . /\
y
I(mut)
.
SM1,Cy
'
m TM6,Ubx n:f(g)
I \
( U s e d as stock for MR experiments)
.' x
SM1,Cy
m TM6,Ubx
)( 2 ; y
sco
.
I-
SM1,Cy
1
m TM6
(Used as stock for MR experiments) FIGURE 1 .-Extraction
procedure for Chromosome I I and Chromosome I I I .
5 , were crossed to tester females. For example, in Cross A of the extracted second chromosome X / Y ; Z(mut)/aZ b c s p ; Sb/lZI males were used, while for the extracted third chromosome X / Y ; Sco/aZ b c s p ; male progeny were selected from generation 4 and crossed to tester females in generation 5. From this cross, all progeny were scored for recombination on the second chromosome. In each case, five or more mass culture crosses were made i n generation 4, with ten or more individual randomly-selected males being mated to two virgin tester females in generation 5. From generation 5, one hundred progeny 03 average were scored from each vial. Mapping of the mutator factor on the second chromosome: A method somewhat analogous to that described by SLATKOand HIRAIZUMI (1975) was followed to place specific portions of the mutant line second chromosome on similar genetic backgrounds. As shown in Figure 3, the multiply marked dpoo cn L bw stock was crossed to the extracted second chromosome stock. From this cross, non-Curly, Stubble females were crossed to Curly, Scutoid, Ubx, Stubble males. F, individual male progeny were double mated, first to the multiply-marked recessive stock females (to ascertain each male's second chromosome genotype), and secondly, to the marked second and third chromosome stock to establish stocks. These stocks, possessing identified portions of the original second chromosomes in marked identical backgrounds, were then tested for their ability to induce male recombination on the second chromosome. RESULTS
The percentage of male recombination observed in the stocks possessing chromosomes extracted from the mutation lines is seen in Table 1. (Percentage male
408
N. N. SCOBIE A N D H. E. SCHAFFER
A ) CHROMOSOME
IC
Cross A x . al b c s p .1 - E t x a1 b c s p
gen. 4 :
- I
x . al
-,
gen. 5 :
x
b c
sp.
x
SM1,Cy
III
\ x
\
,
IIT
Score
Cross
. IImut)
)(
I-
albcsp
Y
m
fbr
-I--;
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IImut)
- 1
al b c s p
x
Sb TM6,Ubx
. Sb I
-
MR
6
gen. 4 :
x . Jh) . Sb -, x
gen. 5 :
SM1,Cy
I
TM6,Ubx
x . albcsp - I
x
albcsp
m ;-
X\
y . a 1 b c s pI .- m x a1 b c sp IU
-1
xr; JII
c
Score for
MR
t
I(mut)
. Sb I -
a'bcsp
=
6 ) CHROMOSOME Zt Cross A
- Extracted
Cross 8
- Extracted chromosome used in
FIGURE 2.-Procedure recombination.
chromosome used
in the male in gen. 4. the male in gen.
5.
for testing the ability of the extracted chromosomes to induce male
recombination has been expressed as the pooled frequency of male recombinants expressed as a percentage of total progeny.) The highest levels of male recombination were observed when heterozygous males possessing mutation line second chromosomes of male origin were tested. Second chromosomes of female origin showed lower IeveIs of male recombination which, however, were elevated above those values observed in the extracted third chromosomes of either origin. The percentage of males showing the ability to induce male recombination was about 50% for Chromosome ZI when the chromosome being tested was of male origin (the A cross) and dropped to less than 10% in Chromosome lZZ.
409
LOCATION O F MUTATOR FACTOR BY MR
1.
.
x x
2.
- 1
x
3. a)
l(mut) . Sb IdpoVTcn L bw
.
dpoVScn L bw
- I
x
)(
m
dpoV’cn L b w
. Ill
,-
IK
x . Sco . Sb x SM1,Cy TM6,Ubx
b)
- #
x .
- 1
Sco
.
SM1,Cy
*
I,,)(
Sb TM6,Ubx
SM1,Cy R .’ TM6,Ubx Sb
I
stock
4.
S.
x . a l b c s p I -. m x 01 b c SP
- 1
x . - 4
x
al b c s p . m a l b c s p RI I-
x
-
xI .
\,Cy
x
Y . - 1
x
R
Sb TM6,Ubx
R . Sb I albcsp m
Score for recombinants FIGURE 3.-Procedure followed to map the mutator factor on the second chromosome. R = putative recombinant on Chromosome ZI.
Table 2 summarizes the recombination events observed in the progeny of each line tested, by chromosomal origin. The recombinant classes omitted from the table were not observed. It is of interest to note that no reciprocal events were observed among the progeny recovered, and that numerous double crossover recombinants of one type only were identified. Transmission frequencies of the “mutation line” second chromosomes (the k values) were calculated for both chromosomes according to origin, on both a per line basis and a per fly basis. Lower k values were noted to be more frequently associated with individual males among whose progeny male recombinants
410
N. N. SCOBIE A N D H. E. S C H A F F E R
TABLE 1
Percentage male recombination in extracted chromosomes Line
J H 184 J H 192 J H 235
Chromosome I I Cross A Cross B
Chiomosome I11 Cross A Cross
2.09% (54% 1 1.37% (57%) 0.74% (35%)
0.09% ( 7%) 0.07% ( 3%) 0.04% ( 5%)
0.3C% (23%) 0.53% (28%) 0.091% ( 6%)
Cross A-chromosome of male origin; Cross B-chromosome centage of males in which male recombination occurred. 2.200-4,700 progeny/cross.
B
0.03% ( 2%) 0.09% ( 9%) 0.10% ( 7%)
of female origin; (
%)-per-
were found. No such common tendency could be identified in the data from complete lines of any one origin. Males from the recombinant stock (formed from the cross 3b in Figure 3), whose non-Curly second chromosomes possessed identifiable portions of the original mutation line second chromosomes, were tested for their ability to induce male recombination. Recombinant products were recovered in all but three of the independent stocks tested. The results are given in Table 3. The three lines tested in this manner were JH 184 (dp""), JH 192 ( d p " ) and JH 235 ( u g ) . As the markers used in the second chromosome marker stock were dp"" cn L bw,no method existed by which to distinguish the marker chromosome from the original chromosome in the region of the left arm of line JH 184 as both carried dp". Therefore, the data for the dumpy line JH 184 have been tabulated separately to eliminate any ambiguity (rows 18-21). The progeny produced by the crosses of the JH 192 ( d p " ) and JH 235 (vg) recombinant stocks to marker stocks were screened to identify the products of male recombination and provide the following information. TABLE 2
A summary of male recombination in the extracted lines Parentals nlbcsp
Chromosome orgin
Extractedline
++++
Chromosome I I (paternal)
J H 184 J H 192 J H 235 J H 184 J H 192 J H 235 JH 184 J H 192 J H 235 J H 184 J H 192 J H 235
2668 2397 261 1 2163 2201) 1917 2496 1585 2547 1635 1252 1620
Chromosome I1 (maternal) Chromosome I I I (paternal) Chromosome I I I (maternal)
1763 1720 1881 1509 1714 14'35 1764 1183 2113 1253 97s 1322
f b f f
5 8 0 0 3 0 0 0 0 0 1 0
f
f
Recombinants c f a l b f f
54 48 25 11 11 3 3 2 2 1 1 3
16 0 4 0 2 0 1 0 0 0 0 0
albcf
0 1 1 0
5 0 0 0 0 0 0 0
41 1
LOCATIOX O F M U T A T O R FACTOR BY M R
TABLE 3 Percentage of male recombination induced by recombinant second chromosomes
Mutant line
1. J H 235
(w) 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
J H 235 J H 235 JH 235 JH 235 JH 235 JH 235 J H 235 JH 235 J H 235 JH 192 (dP? 12. J H 192 13 JH 192 14. JH 192 15. J H 192 16. J H 192 17. JH 192 18. J H 184 (dP9 19. JH 184 20. J H 184 21. JH 184
Number of independent recombinant stocks tested
k value
2
0 52
737
1.22
1 2 2 1 2 2 2
1
0.63 0.52 0 61 0 55 0 55 0.58 0.57 0.57 0.60 0.55
862 920 985 21 1 660 940 1199 2299 608 399
0 00 0.65 0 00 0.47 0.00 0 53 0.50 0.52 0.00 0.75
+ +++ +
2 1 2 3 1 1 4
0.63 0.60 0.54 0.56 0 53 0.58 0.57
1346 804 1013 1072 479 489 1773
0.00 0.00 1.68 0.84 1.87 0.80 1.12
++ +
1 2 1
0.58 0.61 0.62
361 1360 618
1.10 0.00 0.00
Recombinant chromosome type
++++
dpou cn L bw
+++bw d p o u cn L dpou cn +cnLbw
+ ++
dP0"
+++
+cn++ +cnL+ dpov cn bw dpo
+
+++
dpov cn L bw dpov cn L dpo L bw dpO cn L bw
+
+
dPov dpo cn L dpou 4-4-
dpov bw dpov cn L bw dpov cn L
3 1
Total vrogeny counted
% male recombinants
In no instances were recombinants recovered when only the complete multiply marked chromosome was used (rows 2 and 12). In all cases, recombinants were recovered when the entire extracted second chromosome was present (rows 1 and 11). No recombinants were identified when the only segment of the original extracted second chromosome present was the region located to the right of L and including bw (rows 4 and 13). If the results in Table 3 are observed on a per line basis, the following may be noted. In line JH 235 (vg) recombinants are observed only in lines in which the common portion of the mutation line chromosome present is a region in 2R lying to the right of L and to the left of bw and including neither of them. In the JH 192 (dp") line, recombinants exist only in the lines where the common portion of the mutation line chromosome always present is a region in 2L between, yet not including, the markers dpov and cn. Transmission frequencies of the recombinant stock chromosome from the heterozygous males ( k values) are also given in Table 3. In every case, lines in which male recombination was identified possess k values which are lower than the values obtained in lines that carried chromosomes which caused no male recombination. (k values for lines in which male recombination was identified
412
N. N. SCOBIE A N D H. E. S C H A F F E R
fall between 0.52 and 0.58. k values for lines with no male recombination, with the exception of row 6, are between 0.60 and 0.63.) Two other features already seen to be characteristic of male recombination in this study were observed again in this experiment. Numerous recomb’lnants recovered were formed as a result of double crossovers, and the observation reciprocal recombination types was extremely rare. DISCUSSION
YAMAGUCHI and MUKAI(1974) argued that a mutator factor existed on the second, or possibly the third, chromosome in the lines currently being studied. Their assumption, coupled with the evidence from reversions and male recombination found in the original lines in this study (SCOBIEand SCHAFFER 1982) provided the justification for extracting and testing the second and third chromosomes for their ability to induce male recombination on the second chromosome. I n the current study, the factor responsible for inducing male recombination is shown to be associated with the presence of the second chromosome. In the three lines tested ( J H 184, JH 192 and JH 2 3 5 ) , nontrivial frequencies of male recombination were induced on the second chromosome when the extracted second chromosome of male origin was present. Thus, the JH and AW lines can be designated as P lines, although lines that have been maintained in a laboratory f o r many years would customarily be expected to react as M strains (KIDWELL, KIDWELLand SVED1977). When a trait is inherited in a set of lines in a nonreciprocal manner, the lines are designated as P lines if the trait is inherited through the male, and as M lines if the characteristic is inherited through the mother. In this case, cage population samples from which the JH and AW lines originated were tested independently by M. G. KIDWELL(C. C. LAURIE-AHLBERG, personal communication) and, similarly, were found to act as P strains. When the origin of the two chromosomes that were extracted and tested for their ability to induce male recombination is considered, it is noted that the second chromosome only has been maintained from the original cage population. At the time of this study, the original JH and AW lines, possessing a recessive-lethal carrying second chromosome balanced over Curly, had been maintained by single-pair brother-sister matings for approximately 240 generations. The wild third chromosome would have been replaced quite rapidly by that from the Curly C-160 stocks, an event alluded to by YAMAGUCHI and MuKAI (1974). Thus, a factor possessing the ability to induce male recombination is being sought in a second chromosome derived from nature and in a third chromosome probably derived from a very long-standing laboratory stock, both of which have been associated with laboratory C-160 cytoplasm. Second chromosome multiple-marker and balancer stocks have been noted to behave as M strains. Specifically, KIDWELL(1979) has tested a Cy*/Bl L2stock and verified it as an M strain. Therefore, both the originaI SM1, Cy balancer and the SM1; TM6 stock, the genetic background in which the extracted chromosomes in this study were placed, are, with a fairly high degree of certainty, M strains. The composition of the stock carrying the extracted JH second chro-
LOCATION O F MUTATOR FACTOR BY MR
413
mosomes is then most likely that of a P factor in an M cytotype. In all cases, the second chromosome tester stock with which the extracted lines were crossed was al b c sp, It is very probably also an M strain; KIDWELL and KIDWELL (1975) classified an al cl b c spe stock as M. It therefore logically follows that male recombination would be observed as a result of a cross between any strain carrying a P factor (irrespective of its cytotype) and a strain with M cytotype. Such an interpretation provides a reason for the observed male recombination in the B cross of the extracted second chromosomes in the JH 184 and JH 192 lines. Low levels of male recombination observed when the extracted third chromosomes were tested substantiate that they act similarly to those of M type strains and carry no major mutator element. The hypothesis that the mutator factors are transposable inserted sequences of DNA or that several minor elements may also exist, would explain the occasional recovery of a recombinant event from stocks carrying the extracted third chromosome only (HIRAIZUMI et al. 1973; SLATKOand HIRAIZUMI 1975). In these cases, a minor element transposed from the second to the third chromosome would explain the trivial levels of male recombination observed. A simpler explanation of their presence is to assume that the occasional occurrence of male recombination is a normal event in all strains of D. melanogaster. The male recombination observed in the extracted second chromosome lilies demonstrates several additional characteristics also reported by other investigators including HIRAIZUMI (1971 and 1977), KIDWELLand KIDWELL(1976), and ENGELS(1979a). The percentage of males showing the ability to induce male recombination is about 50% when the extracted second chromosome of male origin is present. (This percentage drops to less than 10% when the extracted third chromosome is present.) The transmission frequency of the l(mut) chromosome in the A cross when Chromosome ZZ is present is negatively correlated with the presence of male recombination. Table 2 demonstrates two further points. The lack of reciprocal recombinational products is striking. Recently, ENGELS(1979a) has also noted the recovery of only one of the two possible recombinant types from male recombination experiments. Of equal interest is the presence of a large number of recombinational events that involve a double (1977) make similar reference to double crossover. WOODRUFF and THOMPSON crossovers in their OK lines. Although the wild caught l ( m u t ) genotype has a higher viability than the marker al b c s p stock, it is in no way sufficiently pronounced to explain the frequent recovery of only c and b progeny. The absence of reciprocal recombinational events and the presence of a comparatively large number of two different double recombinants each possessing a substantial proportion of the l ( m u t ) chromosome indicate that the mechanism causing male recombination is different from that which is responsible for the “normal” type of crossing-over observed in females (SLATKO 1978; K. A. MATTHEWS, unpublished results). The results obtained from line JH 192 ( d p ” ) and JH 235 (vg) in the mapping experiment indicate that the presence of the entire extracted second chromosome continued to induce male recombination, while the marker chromo-
++ +
+ ++
414
N . N. SCOBIE AND H . E. SCHAFFER
some used to identify specific regions of the extracted chromosome was unable to induce such effects. Male recombination did not occur among progeny from crosses where only the region to the right of the original chromosome, including the bw marker, was present. Upon further analysis, it appears that male recombination can be induced in the presence of a distinct and different portion of the chromosome in the JH 235 and the JH 192 lines. In J H 235, the chromosomes that produced recombinants are seen to possess only one region of the original mutant chromosome in common. In Table 3, mutant lines 1, 3, 5, 7, 8 and 9 show that the region falls to the left of bw and to the right of L. Line 5 indicates that a region to the right of and including L can induce recombination while line 3 indicates that a region to the left of and excluding bw is needed. Line 9 shows that recombination occurs in the absence of the L locus. That the factor responsible f o r recombination in the JH 235 line lies between L and bw is substantiated further by the data in lines 4, 6 and 10 where no recombination is induced by the presence of a region including only d p + in line 6 and only L+ in line 10 and only bw+ in line 4. The common region of J H 235 needed to induce recombination is interpreted, therefore, to be absent from both line 10 and line 4. Line JH 192, when similarly analyzed, indicates that a different common region of the mutation line chromosome is necessary if recombination is to be induced. Lines 14, 15 and 17 show that a region of the chromosome apparently including the d p locus is required. Line 16, in which a comparatively high percentage of recombination is observed, indicates that a region to the right of and excluding d p is required. Based on these data a region between d p and cn, yet excluding both of them, must be present if recombination is to occur. The data from line 13 is consistent with this statement. Information provided in lines 18-21 for the J H 184 (dpot') line, in which the origin of 2L to the left of cn cannot be determined, may be interpreted to agree with the findings f o r J H 192 ( d p " ) . If attention is directed to the associated k values of all the lines, a very strong association is evident between the existence of male recombination and low k values. Such a negative correlation is not unique and has been reported by HIRAIZUMI et aE. (1973) and by ENGELS(1979a). The relatively high k values in this study are not associated with male recombination. The above results are consistent with the hypothesis that there exists on the second chromosome an element that is capable of controlling at least two different and distinct mutator factors. In line J H 235, which carries a mutation at the ug locus, the mutator factor has been isolated to a site on 2R between the markers L and bw. I n line JH 192, originally identified by the presence of dpo at the d p locus, the mutator factor is located Eetween d p and cn. The controlling element on the second chromosome could be hypothesized to function as a distinct unit responsible for the activity of different specific mutator elements that are responsible for the expression of hybrid dysgenic phenotypes in different lines. Alternatively, the mutator element could be envisaged as a transpos-
LOCATION O F MUTATOR FACTOR BY M R
415
able element that is itself capable of shifting from one location to another on the same (or possibly a different) chromosome within a set of lines of common origin to induce varied hybrid dysgenic expressions such as mutation, male recombination and altered transmission frequencies. An argument somewhat analogous to this is not without precedent and has been demonstrated much more precisely by ENGELS(1979b) in relation to the activity he observes on the X chromosome in the region of the singed locus. In the present study, the proposed mutator factors could have been located to a smaller region had additional markers been used. It remains of interest, therefore, to anticipate the isolation of smaller parts of the original chromosome, within which the two mutator factors were located to identify those portions which retain the ability to induce high levels of male recombination. Similarly, it would be interesting to obtain information from molecular studies of these same regions of Chromosome ZZ to identify and locate the responsible factors. We wish to thank Drs. C. C. LAURIE-AHLBERG and R. R. SEDEROFF for their helpful suggestions throughout the development of this study and Dr. B. E. SLATKO for his critical reading of the manuscript. To Dr. J. M. MASON,we extend our special thanks for his substantial contribution to the analysis of the mapping section. LITERATURE CITED
ENGELS,W. R., 1979a Germ line aberrations associated with a case of hybrid dysgenesis in Drosophila melanogaster males. Genet. Res. Camb. 33: 137-146. -, 19791, Extrachromosomal control of mutability in Drosophila melanogaster. Proc. Natl. Acad. Sci. U.S.A. 76: 40114015.
HIRAIZUMI, Y., 1971 Spontaneous recombination in Drosophila melanogaster males. Proc. Natl. Acad. Sci. U.S.A. 68: 268-270. -, 1977 The relationships among transmission frequency, male recombination and progeny production in Drosophila melanogaster. Genetics 87: 83-93.
HIRAIZUMI, Y., B. SLATKO,C. LANGLEY and A. NILL, 1973 Recombination in Drosophila melanogaster males. Genetics 73 : 439-444. KIDWELL,M. G., 1979 Hybrid dysgenesis in Drosophila melanogaster: two causally independent interaction systems. Genet. Res. Camb. 33: 205-218. KIDWELL,M. G. and J. F. KIDWELL,1975 Cytoplasm-chromosome interactions i n Drosophila melanogaster. Nature 253 : 755-756. , 1976 Selection for male recombination in Drosophila melanogaster. Genetics 84: 333-351. RIDWELL,M. G., J. F. KIDWELLand J. A. SVED,1977 Hybrid dysgenesis in Drosophila melanogaster: a syndrome of aberrant traits including mutation, sterility and male recombination. Genetics 86: 813-833.
D. L. and E. H. GRELL, 1967 Genetic variations in Drosophila melanogaster. CarLINDSLEY, negie Inst. Wash. Publ. No. 627. MUKAI, T. and C. C. COCKERHAM, 1977 Spontaneous mutation rates at enzyme loci in Drosophila melanogaster. Proc. Natl. Acad. Sci. U.S.A. 74: 2514-251 7. 1982 A mutator factor in a strain of Drosophila melanoSCOBIE,N. N. and H. E. SCHAFFER, gaster: identified by use of mutation, reversion rates and male recombination. Genetics 1.00: 417-429. B. E., 1978 Parameters of male and female recombination influenced by the T-007 SLATKO, second chromosome in Drosophila melanogaster. Genetics 90 : 257-276.
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N . N. SCOBIE A N D H. E. SCHAFFER
SLATKO,B. and Y. HIRAIZUMI, 1975 Elements causing male crossing-over in Drosophila melunogaster. Genetics 81 : 3 13-324. VOELKER,R. A., H. E. SCHAPFER and T. MUKAI,1980 Spontaneous allozyme mutations in Drosophila melanoguster: Rate of occurrence and nature of the mutants. Genetics 94: 961-968. WOODRUFF, R. C. and J. N. THOMPSON, 1977 An analysis of spontaneous recombination in Drosophila melunogaster males: Isolation and characterization of male recombination lines. Heredity 38 (3) : 291-307. YAMAGUCHI, 0. and T. MUKAI,1974 Variation of spontaneous occurrence rates of chromosomal aberrations in the second chromosome of Drosophila melanogaster. Genetics 78 : 1209-1221. Corresponding editor: W. W. ANDERSON
