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LINKAGE OF THE GENES FOR BDT AND DIELDRIN RESISTANCE IN LARVAE OF THE MOSQUITO AEDES AEGYPTI JUDITHM. HITCHEN'AND R. J. WOOD Department of Zoology, University of Manchester, Mancherster, MI3 9PL, England The BDT resistance gene RDDT1,and the dieldrin resistance gene R d l have been mapped on linkage group XI with respect to visible markers, in the mosquito Aedes aegypri L. The best interpretation of the data gives the order wa - R ds - R D D T 1 - s - y but wa - R ds - y - s RDDT1 is also possible. h is very loosely linked with RDDT'.The length of the linkage group has been considerably extended from previous studies.
"-
Introduction Previous studies have established linkage between genes for dieldrin- and DDTresistance and linkage group 11 markers (Khan and Brown, 1961; Brown and Abedi, l%2; Klassen and Brown, 1964; Wood, 1967a; lnwang et al. , 1967; Lockhart et al., 1970). But various interpretations have been placed on gene order. The present investigation re-examines this and positions some markers not previously used. Materials and Methods The following strains were used in these experiments: A. Resistant Strains 1. I3ANCKOK-HR Resistant to DDT, otherwise wild type. Larval mortality at 50 pprn DDT (24h) = 5%. Resistance remained stable over a period of two years, in the absence of selection. 2. TRINIDAD-T8 Resistant to DDT, otherwise wild type. Mortality at 50 ppm BDT (24 h) = 2.5%. 3. ISLA VERBE Resistant to dieldrin, otherwise wild type. Mortality in larvae exposed to 5 ppm dieldrin (24 h) = 63.0%. 4. BANGKOK-HR wart, dark scuturn Produced by reciprocally crossing the wa ds s y strain (see below) with BANGKOK-HR, selecting F2 individuals which showed uniform expression of the markers wart and dark scuturn and selecting with DDT from the F, onwards. F6mortality at 50 pprn DDT (24 h) = 90%, LT,, (50 pprn DDT) = 5.6 h. 5. BANGKOK-HR spot Produced as described above (4). Mortality in F, larvae at 50 ppm DDT (24 h) = 55% LT,, (50 ppm DDT) = 16 h.
B . Susceptible Strains 1. QS.Wild type. Larval LC (24 h) = 0.05 pprn DDT. 2. Wart, dark scuturn, spot, yellow (wa ds s y). Homozygous for the larval marker yellow @) and the adult markers wart (wa) dark scutum (ds) and spot (s), all on linkage group II. Susceptible to BDT and dieldrin: larval mortality at 0.5 pprn DDT (5 h) = 100.0% at 0.5 pprn dieldrin (5 h) = 100.0%. 3. Halteres. Homozygous for the adult marker halteres (h) on linkage group 11. Almost fully susceptible to DDT in larvae: larval mortality at 0.5 ppm (5 h) = 87%. 'Present address: Matthew Boulton College, Birmingham B5 7DB,England. Manuscript received July 22, 1974.
Can. J. Genet. Cytol. 17: 543-551,1975.
Can. J. Genet. Cytol. Downloaded from www.nrcresearchpress.com by LEHIGH UNIVERSITY on 12/13/14 For personal use only.
544
J . M. MITCHEN AND R. J . WOOD
Linkage relationships were established using two and three point test cross data from reciprocal backcrosses: Fl (susceptible x resistant) x susceptible. There were two types of parental cross: those in which the susceptible chromosome was marked with one or more recessive visible mutants (resistance in coupling with wild-type); and those in which the resistant chromosome carried the markers (resistance in repulsion with wild-type). When necessary, corrections for partial manifestation (incomplete penetrance) were made (Bailey, 1961). Methods of rearing and testing fourth !tage larvae with insecticides were as described by Wood (1967a, b). The concentration/exposure time selected to differenwas the minimum required to kill tiate susceptibles (+/+) and heterozygotes (RDDTB/+) all susceptibles (0.5 ppm for 5 h). Survivors of insecticide tests were rinsed, removed to clear water and fed. Any "post treatment mortality" which occurred within 24 h of exposure was recorded and added to the ~nortalityat the end of the test, to give the total mortality. The sexes were separated at the pupal stage and the adults were examined for markers within 24 h of emergence. All crosses were mass-naatings using at least 20 of each sex. F, individuals were checked for the presence of markers which, if present, were removed before backcrossing.
Results DDT Resisda~zcein BANGKOK-HR Experiment I The wa ds s susceptible strain was crossed reciprocally with BANGKOK-HR, resistance in coupling with wild type (wa ds s x + + + RDDT1). F, larvae were subjected to 0.5 ppm DDT for 5 h, an exposure which killed 100% susceptibles. This procedure was designed to remove any susceptible segregants (taking into account the possibility that the resistant strain might not be fully homozygous). Mortality in the reciprocal F,'s was minimal:
+
Mortality (%) 100.00 0.50 0.25
+
wadss F1 (HR x wa ds s +) F, (wa ds s x HR)
+
No. tested 245 400 400
+
Surviving F1 individuals were backcrossed to wa ds s and the larval progeny exposed to 0.5 ppm DDT for 5 h. Survivors were scored for the markers as adults. The results, shown in Table I (Expt. 1) where mortality was 50.8 9 0.696, are in good agreement with a 1: 1 ratio (X: = 0.004, p > 0.99). Calculated values of recombination between the four loci are given. The values tabulated assume the gene order shown (for a discussion of gene order, see below). Two values were obtained for some gene pairs, using different combinations of three loci. The greater value has been tabulated in each case. Experiment 2 A reciprocal cross, resistance in repulsion with wild type, was made between BANGKOK-HR, wart, dark scutum and Q S . (wa ds R ""*' x +). The F, larval were exposed to 0.5 ppm DDT for 5 h.
++
QS F, (wa ds R ~ x QS) ~ ~ F, (QS x wads RDDT')
I
Mortality (9%) 99.0 7.9 12.3
No. tested 200 229 400
545
DDT AND DIELDRIN RESISTANCE IN MOSQUITO
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+
'.
The extent of F, mortality probably indicates a low frequency of alleles transmitted to F, individuals by the marked "resistant" parent. ~urvlvorswere backcrossed to wa ds + and the progeny exposed to 0.5 ppm DDT for 5h. Markers were scored in adults derived from the survivors. The results, shown in Table I, indicate a mortality of 48.5 c 0.8%, just significantly different from the expected 50% (Xb = 4.23, p < 64.05), although this was due to the effect of one reciproca! only. Calculated values of recombination are given (Table I, Expt. 2). Experilnent 3 A reciprocal cross, resistance in repulsion with wold type, was made between BANGKOK-HR, spot and Q S . (s R DDT1 x +). F, larvae were exposed to 0.5 pprn for 5
+
h. Mortality (%) 99.0 33.2 20.8
QS PI (9 W DDT1 x QS) F (QS >< s R ""'I)
,
No. tested 200 250 250
Clearly, the F, showed a lower tolerance than expected on the basis of homozygosity for IPDwr1 in the resistant parent. Hence the particular need in this experiment to select the F, before backcrossing. Surviving F, larvae were backcrossed to s + and the progeny were exposed to 0.5 ppm DDT for 5 h. Survivors were scored for the marker. The results are shown in Table I. Mortality was 56.3 1 1.295, significantly greater than 50% (Xf = 25-50, p < 0.001), probably due to a seduced tolerance of +/RDDTBgenotypes against the genetic background of this particular cross, rather than an excess of +/+ genotypes; the latter was rendered unlikely by selection of the F,. Despite the higher than expected mortality, the value of recombination, s - R D"T" obtained from these figures (Table I, Expt. 3), agrees closely with that obtained from other crosses (Table I, Expt. 1; Table TI). Experinme~t4 A reciprocal cross, resistance in coupling with wild type, was made between the halteres strain and BANGKOK-HR (h + x RDDn). Since the halteres strain showed some tolerance to DDT, F, larvae were exposed to 0.5 ppm DDT for an extra hour (6h).
+
Mortality (%) $7 .O 0.8 0.8
halteres F, (halteres X HW) F, (HR x halteres)
No. tested 200 250 250
+
Survivors were backcrossed to h and backcross larvae exposed to 0.5 pprn DDT for 6 h before scoring for the marker. Mortality in the backcrosses was 48.9 & 0.8% (X ;* = 1.71, p > 0.10) apparently indicating good discrimination between + / and + / R DDT1 genotypes (Table I). The value of recombination between h and R DDTL of 43.7 2 1.4% was high, but linkage was indicated. (X: = 38.22, p < 0.00 1). The mutant hakteres was not always easy to score, although the untested backcross (sibs of those tested) gave a ratio of 131 h : 134 h (Xq:, 0.02, p > 0.80).
+
+
-
DDT Resistance in TRINIDAD-T8 Experiment 4 The marked susceptible stock was the same as that used in a cross with BANGKOK-MR (Table I, Expt. I ) , enabling a comparison to be made between the two resistant strains (BANGKOK-HR and TRINIDAD-T8). The cross was made with
wads + s ++R+
-
-
wa-R ds-R wa-ds
wa-R s-R ds-R wa-s S-ds wa-ds
Genes tested
This represents approximately half the progeny since only the survivors of DDT exposure, i.e. the R phenotypes, may be scored for markers. 'Not all R phenotypes were scored for markers (random sample taken).
1
Experiment
Genotype of heterozygous parent
TABLEX Test of linkage relationships of R D*Vlla9vJ DDT-resistance) in BANGKOK-HR strain (R DDTGs abbreviated to R) % mortality Total +- SE scored2 (no. exposed)
recombination +- SE
%,
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--
wads + s ++R+
d k
-
.-
Genotvoes of heterozygous parent
-
wadss+ 54
wadssy 709
++s
+
wa+sy 186
+ds 123
22
+ ds s
+
Phenotypes of progeny1
wa + s 65
48
-
wa 830
++
wadss 39
-
+
wa+s+ 64
869
+++
wa ds 319 23 15
Totd scored2
-
53.5 + 0.6 (6869)
(no. exposed)
+ SE
5% mortality
Test of linkage relationships of R DDT1 (larval DDT-resistance) in TRINIDAD T8 strain (RDDT5s abbreviated to R )
y-s
wa-ds s-ds y-wa
wa-s
wa-R S-R ds-R wa-s s-dr wa-ds
Genes tested
9%
44.5 + 0.9 (43.0 2 1.0) 39.5 2 0.9 (37.3 + 1.0) 29.4 +- 0.8 45.8 rt 0.9 (46.1 ? 1.3) 21.2 + 0.7 (14.1 2 0.8)
60.4 2 1 .O 7.5 + 0.6 21.7 +- 0.9 60.8 + 1 .0 26.6 + 0.9 44.9 + 1.1
recombination & SE
'This represents approximately half the progeny in the first experiment, i.e. the R phenotypes, since only the survivors of DDT exposure may be scored for markers. 2Notall R phenotypes were scored for markers (random sample taken). Recombination values in brackets are corrected for partial manifestation ofwa and))+according to Bailey (1961).
Experiment
--
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548
J . M. HITCHEN AND R. J. WOOD
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resistance in coupling with wild type (wa ds s to 0.5 ppm DDT for 5h.
+ x + + + RDD") F, larvae were exposed Mortality (%) 100.0 1.3 3.6
wa ds s F, (T8 x wa ds s +) F1 (wa ds s x T8)
+
No. tested 245 300 306
+
Surviving F1 larvae were backcrossed to wa ds s and the backcross larvae exposed to Q.5 ppm DDT for 5h. Mortality at 53 - 5 2 0.6% was significantly higher than the expected 50% (Xf = 33.12, p < 0.001). (See also BANGKOK-HR, Expt. 3). Recombination values are shown in Table II. The large recombination values involving the wa gene are notable. Moreover there is an excess of wa phenotypes, whereas an excess of wa+ is expected. Partial manifestation (incomplete penetrance) or mis-scoring of wa would account for both these observations. +
Experiment 2 A second cross in this series (wa ds s p, x + +) was identical to that described above, except that no mosquitoes were exposed to insecticide at any stage, and the larval markeryellow (y) was scored. The backcross to wa ds s y gave additional linkage data for the visible markers on linkage group I1 and eliminated possible errors due to insecticide testing. Segregation ratios involvingy and w a deviated from 1:1
+ +
Alleles y :y+ 1va : M'a+
Ratio 1877 : 1307 1886 : 1298
Deviation from 1: f X,2 = 102.04, p < 0.001 X @= 108.59, p < 0.001
Differential mortality of y is unlikely since s (closely linked toy) is not depleted: ratio s:s is 1: 1 (X" 1.54, p > 0.20). Partial manifestation of y (yf+y) previously observed by Craig and Gillham (1 959) seems more likely. The penetrance of y in the present case is calculated to be 82%. Differential mortality of waf is a possibility, although there is much greater distortion in males (1 107 wa : 629 wa +,X,2 = 131-62, p < 0.001) than in females (779 wa: 669 ll9a+,X $2 = 9.36, p < 0.0 1). However, partial manifestation of wa (wa ++wa) seems more likely since some difficulty was experienced in scoring this marker. The '"penetrance" of rva was thus 8 I . 5%. Linkage distances, corrected for partially-manifesting characters (Bailey, 196 1), are shown in Table 11. +
+
+
+
+
+
+
Dieldrin Resistance in ISLA VERDE In order to relate the locus for larval dieldrin resistance (R with visible markers, reciprocal crosses in coupling were made between the wa ds s and ISLA VERDE strains x R d3. The F1 was not exposed to a discriminating concentration (wa ds s before backcrossing to wa ds s since preliminary tests showed very little mortality in the reciprocal Fls at the concentration which killed all susceptibles.
+
+
+++
+
wadss F, (wa ds d X ISLA VERDE) Fp(ISLA VERDE X wa ds s +)
+
Mortality (9%) 100.00 0.80 0.33
No. Tested 250 300 300
_
_
-
-
_
271
++
86
wa ds s
wa
C
_
_
-
_
_
-
+s
_
_
186 _
246 _
+ ds +
142
+ ds s
+ +s
99
wa
+ 236 1
___-
____C__------~
+++
wa ds 59
1272 ______---_
_
---_
49.5 + 0.7 (478 1 )
__--
-
-
-
s-d~
wa-ds
wa-s
wa-R S-R ds-R
'This represen& approx~matelyhalf the progeny since only the suwivon of dirldrln exposure, i.e. R phenotypes, may be scored for markers. 2Nnt all R phenotypes were scored for markers (random sample taken).
_
__
M~U
ds s + +++R
Genotype of heterozygous parent
TABLEIHn Test of linkage relationships of R" (larval dieldrin resistance) in ISLA VERDE strain (R is abbreviated to R ) __ --____ _ _ ____ _ _ ___ _--_ _ _ _ - _ _ - _ - __ _____
LINKAGE OF THE GENES FOR BDT AND DIELDRIN RESISTANCE IN LARVAE OF THE MOSQUITO AEDES AEGYPTI JUDITHM. HITCHEN'AND R. J. WOOD Department of Zoology, University of Manchester, Mancherster, MI3 9PL, England The BDT resistance gene RDDT1,and the dieldrin resistance gene R d l have been mapped on linkage group XI with respect to visible markers, in the mosquito Aedes aegypri L. The best interpretation of the data gives the order wa - R ds - R D D T 1 - s - y but wa - R ds - y - s RDDT1 is also possible. h is very loosely linked with RDDT'.The length of the linkage group has been considerably extended from previous studies.
"-
Introduction Previous studies have established linkage between genes for dieldrin- and DDTresistance and linkage group 11 markers (Khan and Brown, 1961; Brown and Abedi, l%2; Klassen and Brown, 1964; Wood, 1967a; lnwang et al. , 1967; Lockhart et al., 1970). But various interpretations have been placed on gene order. The present investigation re-examines this and positions some markers not previously used. Materials and Methods The following strains were used in these experiments: A. Resistant Strains 1. I3ANCKOK-HR Resistant to DDT, otherwise wild type. Larval mortality at 50 pprn DDT (24h) = 5%. Resistance remained stable over a period of two years, in the absence of selection. 2. TRINIDAD-T8 Resistant to DDT, otherwise wild type. Mortality at 50 ppm BDT (24 h) = 2.5%. 3. ISLA VERBE Resistant to dieldrin, otherwise wild type. Mortality in larvae exposed to 5 ppm dieldrin (24 h) = 63.0%. 4. BANGKOK-HR wart, dark scuturn Produced by reciprocally crossing the wa ds s y strain (see below) with BANGKOK-HR, selecting F2 individuals which showed uniform expression of the markers wart and dark scuturn and selecting with DDT from the F, onwards. F6mortality at 50 pprn DDT (24 h) = 90%, LT,, (50 pprn DDT) = 5.6 h. 5. BANGKOK-HR spot Produced as described above (4). Mortality in F, larvae at 50 ppm DDT (24 h) = 55% LT,, (50 ppm DDT) = 16 h.
B . Susceptible Strains 1. QS.Wild type. Larval LC (24 h) = 0.05 pprn DDT. 2. Wart, dark scuturn, spot, yellow (wa ds s y). Homozygous for the larval marker yellow @) and the adult markers wart (wa) dark scutum (ds) and spot (s), all on linkage group II. Susceptible to BDT and dieldrin: larval mortality at 0.5 pprn DDT (5 h) = 100.0% at 0.5 pprn dieldrin (5 h) = 100.0%. 3. Halteres. Homozygous for the adult marker halteres (h) on linkage group 11. Almost fully susceptible to DDT in larvae: larval mortality at 0.5 ppm (5 h) = 87%. 'Present address: Matthew Boulton College, Birmingham B5 7DB,England. Manuscript received July 22, 1974.
Can. J. Genet. Cytol. 17: 543-551,1975.
Can. J. Genet. Cytol. Downloaded from www.nrcresearchpress.com by LEHIGH UNIVERSITY on 12/13/14 For personal use only.
544
J . M. MITCHEN AND R. J . WOOD
Linkage relationships were established using two and three point test cross data from reciprocal backcrosses: Fl (susceptible x resistant) x susceptible. There were two types of parental cross: those in which the susceptible chromosome was marked with one or more recessive visible mutants (resistance in coupling with wild-type); and those in which the resistant chromosome carried the markers (resistance in repulsion with wild-type). When necessary, corrections for partial manifestation (incomplete penetrance) were made (Bailey, 1961). Methods of rearing and testing fourth !tage larvae with insecticides were as described by Wood (1967a, b). The concentration/exposure time selected to differenwas the minimum required to kill tiate susceptibles (+/+) and heterozygotes (RDDTB/+) all susceptibles (0.5 ppm for 5 h). Survivors of insecticide tests were rinsed, removed to clear water and fed. Any "post treatment mortality" which occurred within 24 h of exposure was recorded and added to the ~nortalityat the end of the test, to give the total mortality. The sexes were separated at the pupal stage and the adults were examined for markers within 24 h of emergence. All crosses were mass-naatings using at least 20 of each sex. F, individuals were checked for the presence of markers which, if present, were removed before backcrossing.
Results DDT Resisda~zcein BANGKOK-HR Experiment I The wa ds s susceptible strain was crossed reciprocally with BANGKOK-HR, resistance in coupling with wild type (wa ds s x + + + RDDT1). F, larvae were subjected to 0.5 ppm DDT for 5 h, an exposure which killed 100% susceptibles. This procedure was designed to remove any susceptible segregants (taking into account the possibility that the resistant strain might not be fully homozygous). Mortality in the reciprocal F,'s was minimal:
+
Mortality (%) 100.00 0.50 0.25
+
wadss F1 (HR x wa ds s +) F, (wa ds s x HR)
+
No. tested 245 400 400
+
Surviving F1 individuals were backcrossed to wa ds s and the larval progeny exposed to 0.5 ppm DDT for 5 h. Survivors were scored for the markers as adults. The results, shown in Table I (Expt. 1) where mortality was 50.8 9 0.696, are in good agreement with a 1: 1 ratio (X: = 0.004, p > 0.99). Calculated values of recombination between the four loci are given. The values tabulated assume the gene order shown (for a discussion of gene order, see below). Two values were obtained for some gene pairs, using different combinations of three loci. The greater value has been tabulated in each case. Experiment 2 A reciprocal cross, resistance in repulsion with wild type, was made between BANGKOK-HR, wart, dark scutum and Q S . (wa ds R ""*' x +). The F, larval were exposed to 0.5 ppm DDT for 5 h.
++
QS F, (wa ds R ~ x QS) ~ ~ F, (QS x wads RDDT')
I
Mortality (9%) 99.0 7.9 12.3
No. tested 200 229 400
545
DDT AND DIELDRIN RESISTANCE IN MOSQUITO
Can. J. Genet. Cytol. Downloaded from www.nrcresearchpress.com by LEHIGH UNIVERSITY on 12/13/14 For personal use only.
+
'.
The extent of F, mortality probably indicates a low frequency of alleles transmitted to F, individuals by the marked "resistant" parent. ~urvlvorswere backcrossed to wa ds + and the progeny exposed to 0.5 ppm DDT for 5h. Markers were scored in adults derived from the survivors. The results, shown in Table I, indicate a mortality of 48.5 c 0.8%, just significantly different from the expected 50% (Xb = 4.23, p < 64.05), although this was due to the effect of one reciproca! only. Calculated values of recombination are given (Table I, Expt. 2). Experilnent 3 A reciprocal cross, resistance in repulsion with wold type, was made between BANGKOK-HR, spot and Q S . (s R DDT1 x +). F, larvae were exposed to 0.5 pprn for 5
+
h. Mortality (%) 99.0 33.2 20.8
QS PI (9 W DDT1 x QS) F (QS >< s R ""'I)
,
No. tested 200 250 250
Clearly, the F, showed a lower tolerance than expected on the basis of homozygosity for IPDwr1 in the resistant parent. Hence the particular need in this experiment to select the F, before backcrossing. Surviving F, larvae were backcrossed to s + and the progeny were exposed to 0.5 ppm DDT for 5 h. Survivors were scored for the marker. The results are shown in Table I. Mortality was 56.3 1 1.295, significantly greater than 50% (Xf = 25-50, p < 0.001), probably due to a seduced tolerance of +/RDDTBgenotypes against the genetic background of this particular cross, rather than an excess of +/+ genotypes; the latter was rendered unlikely by selection of the F,. Despite the higher than expected mortality, the value of recombination, s - R D"T" obtained from these figures (Table I, Expt. 3), agrees closely with that obtained from other crosses (Table I, Expt. 1; Table TI). Experinme~t4 A reciprocal cross, resistance in coupling with wild type, was made between the halteres strain and BANGKOK-HR (h + x RDDn). Since the halteres strain showed some tolerance to DDT, F, larvae were exposed to 0.5 ppm DDT for an extra hour (6h).
+
Mortality (%) $7 .O 0.8 0.8
halteres F, (halteres X HW) F, (HR x halteres)
No. tested 200 250 250
+
Survivors were backcrossed to h and backcross larvae exposed to 0.5 pprn DDT for 6 h before scoring for the marker. Mortality in the backcrosses was 48.9 & 0.8% (X ;* = 1.71, p > 0.10) apparently indicating good discrimination between + / and + / R DDT1 genotypes (Table I). The value of recombination between h and R DDTL of 43.7 2 1.4% was high, but linkage was indicated. (X: = 38.22, p < 0.00 1). The mutant hakteres was not always easy to score, although the untested backcross (sibs of those tested) gave a ratio of 131 h : 134 h (Xq:, 0.02, p > 0.80).
+
+
-
DDT Resistance in TRINIDAD-T8 Experiment 4 The marked susceptible stock was the same as that used in a cross with BANGKOK-MR (Table I, Expt. I ) , enabling a comparison to be made between the two resistant strains (BANGKOK-HR and TRINIDAD-T8). The cross was made with
wads + s ++R+
-
-
wa-R ds-R wa-ds
wa-R s-R ds-R wa-s S-ds wa-ds
Genes tested
This represents approximately half the progeny since only the survivors of DDT exposure, i.e. the R phenotypes, may be scored for markers. 'Not all R phenotypes were scored for markers (random sample taken).
1
Experiment
Genotype of heterozygous parent
TABLEX Test of linkage relationships of R D*Vlla9vJ DDT-resistance) in BANGKOK-HR strain (R DDTGs abbreviated to R) % mortality Total +- SE scored2 (no. exposed)
recombination +- SE
%,
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--
wads + s ++R+
d k
-
.-
Genotvoes of heterozygous parent
-
wadss+ 54
wadssy 709
++s
+
wa+sy 186
+ds 123
22
+ ds s
+
Phenotypes of progeny1
wa + s 65
48
-
wa 830
++
wadss 39
-
+
wa+s+ 64
869
+++
wa ds 319 23 15
Totd scored2
-
53.5 + 0.6 (6869)
(no. exposed)
+ SE
5% mortality
Test of linkage relationships of R DDT1 (larval DDT-resistance) in TRINIDAD T8 strain (RDDT5s abbreviated to R )
y-s
wa-ds s-ds y-wa
wa-s
wa-R S-R ds-R wa-s s-dr wa-ds
Genes tested
9%
44.5 + 0.9 (43.0 2 1.0) 39.5 2 0.9 (37.3 + 1.0) 29.4 +- 0.8 45.8 rt 0.9 (46.1 ? 1.3) 21.2 + 0.7 (14.1 2 0.8)
60.4 2 1 .O 7.5 + 0.6 21.7 +- 0.9 60.8 + 1 .0 26.6 + 0.9 44.9 + 1.1
recombination & SE
'This represents approximately half the progeny in the first experiment, i.e. the R phenotypes, since only the survivors of DDT exposure may be scored for markers. 2Notall R phenotypes were scored for markers (random sample taken). Recombination values in brackets are corrected for partial manifestation ofwa and))+according to Bailey (1961).
Experiment
--
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548
J . M. HITCHEN AND R. J. WOOD
Can. J. Genet. Cytol. Downloaded from www.nrcresearchpress.com by LEHIGH UNIVERSITY on 12/13/14 For personal use only.
resistance in coupling with wild type (wa ds s to 0.5 ppm DDT for 5h.
+ x + + + RDD") F, larvae were exposed Mortality (%) 100.0 1.3 3.6
wa ds s F, (T8 x wa ds s +) F1 (wa ds s x T8)
+
No. tested 245 300 306
+
Surviving F1 larvae were backcrossed to wa ds s and the backcross larvae exposed to Q.5 ppm DDT for 5h. Mortality at 53 - 5 2 0.6% was significantly higher than the expected 50% (Xf = 33.12, p < 0.001). (See also BANGKOK-HR, Expt. 3). Recombination values are shown in Table II. The large recombination values involving the wa gene are notable. Moreover there is an excess of wa phenotypes, whereas an excess of wa+ is expected. Partial manifestation (incomplete penetrance) or mis-scoring of wa would account for both these observations. +
Experiment 2 A second cross in this series (wa ds s p, x + +) was identical to that described above, except that no mosquitoes were exposed to insecticide at any stage, and the larval markeryellow (y) was scored. The backcross to wa ds s y gave additional linkage data for the visible markers on linkage group I1 and eliminated possible errors due to insecticide testing. Segregation ratios involvingy and w a deviated from 1:1
+ +
Alleles y :y+ 1va : M'a+
Ratio 1877 : 1307 1886 : 1298
Deviation from 1: f X,2 = 102.04, p < 0.001 X @= 108.59, p < 0.001
Differential mortality of y is unlikely since s (closely linked toy) is not depleted: ratio s:s is 1: 1 (X" 1.54, p > 0.20). Partial manifestation of y (yf+y) previously observed by Craig and Gillham (1 959) seems more likely. The penetrance of y in the present case is calculated to be 82%. Differential mortality of waf is a possibility, although there is much greater distortion in males (1 107 wa : 629 wa +,X,2 = 131-62, p < 0.001) than in females (779 wa: 669 ll9a+,X $2 = 9.36, p < 0.0 1). However, partial manifestation of wa (wa ++wa) seems more likely since some difficulty was experienced in scoring this marker. The '"penetrance" of rva was thus 8 I . 5%. Linkage distances, corrected for partially-manifesting characters (Bailey, 196 1), are shown in Table 11. +
+
+
+
+
+
+
Dieldrin Resistance in ISLA VERDE In order to relate the locus for larval dieldrin resistance (R with visible markers, reciprocal crosses in coupling were made between the wa ds s and ISLA VERDE strains x R d3. The F1 was not exposed to a discriminating concentration (wa ds s before backcrossing to wa ds s since preliminary tests showed very little mortality in the reciprocal Fls at the concentration which killed all susceptibles.
+
+
+++
+
wadss F, (wa ds d X ISLA VERDE) Fp(ISLA VERDE X wa ds s +)
+
Mortality (9%) 100.00 0.80 0.33
No. Tested 250 300 300
_
_
-
-
_
271
++
86
wa ds s
wa
C
_
_
-
_
_
-
+s
_
_
186 _
246 _
+ ds +
142
+ ds s
+ +s
99
wa
+ 236 1
___-
____C__------~
+++
wa ds 59
1272 ______---_
_
---_
49.5 + 0.7 (478 1 )
__--
-
-
-
s-d~
wa-ds
wa-s
wa-R S-R ds-R
'This represen& approx~matelyhalf the progeny since only the suwivon of dirldrln exposure, i.e. R phenotypes, may be scored for markers. 2Nnt all R phenotypes were scored for markers (random sample taken).
_
__
M~U
ds s + +++R
Genotype of heterozygous parent
TABLEIHn Test of linkage relationships of R" (larval dieldrin resistance) in ISLA VERDE strain (R is abbreviated to R ) __ --____ _ _ ____ _ _ ___ _--_ _ _ _ - _ _ - _ - __ _____
