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Increased Variation in ADH Enzyme Activity in Drosophila

Mutation-Accumulation Experiment Is Not Due to Transposable

Elements at the

Adh Structural Gene

Charles F. Aquadro,*>’ Hidenori TachidaT2 Charles

H. Langley,*’3

KO

Harada* and

Terumi Mukai*

*Laboratory of Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709,’ Department of Statistics, North Carolina State University, Raleigh, North Carolina 27695-8203, and $Department of Biology,

Kyushu University, Fukuoka 812, Japan Manuscript received January 8, 1990 Accepted for publication August 9, 1990

ABSTRACT

We present here a molecular analysis of the region surrounding the structural gene encoding alcohol dehydrogenase (Adh) in 47 lines of Drosophila melanogaster that have each accumulated mutations for 300 generations. While these lines show a significant increase in variation of alcohol dehydrogenase enzyme activity compared to control lines, we found no restriction map variation in a 13-kb region including the complete Adh structural gene and roughly 5 kb of both 5 ‘ and 3‘ sequences. Thus, the rapid accumulation of ADH activity variation after 28,200 allele generations does not appear to have been due to the mobilization of transposable elements into or out of the Adh structural gene region.

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UANTITATIVE variation in phenotype sidered to be the “stuff of evolution” (LEWON- is con-

TIN 1974). However, little progress has been made

toward determining the precise genetic and molecular sources of this variation. Does the source of variation

lie at the structural gene in coding sequences, in

tightly linked regulatory sequences, and/or at separate modifier loci? A large number of classical spontaneous mutations at genetically well characterized loci in Dro- sophila melanogaster have been traced either t o t h e insertion or imprecise excision of transposable ele-

ments within or adjacent to the transcriptional unit of

the structural gene for the character, or to chromo- some rearrangements associated with transposable ele- ments in dispersed locations (e.g., RUBIN 1983; FIN-

NEGAN a n d FAWCETT 1986; O’HARE 1987; GOLDBERG et d . 1983; DAVIS, SHEN a n d JUDD 1987; LIM 1988). This result has been viewed as evidence that transpos- able elements are the major source of variation in gene expression for adaptive evolution (e.g., SYVANEN

1985; MACKAY 1988), speciation (ROSE a n d DOLITTLE

1983; GINZBURG, BINGHAM a n d Y o 0 1984) and macroevolution (ERWIN a n d VALENTINE 1984).

GREEN (1 988), however, has cautioned that these re-

DR. MUKAI’S coauthors respectfully dedicate this paper to his memory.

Building. Cornell University, Ithaca, New York 14853-2703,

Stii7uokd-ken 4 I I , Japan.

( X f o r n i a 9 5 6 1 6 .

Present address: Section of Genetics and Development, Biotechnology

Present address: National Institute of Genetics, I , 1 1 1 Yata, Mishima,

Present address: Department ofGenetics, UniversityofCalifornia, Davis,

(;rnrtin 126: 915-919 (December, 1990)

sults may provide a biased view of spontaneous mu- tations in nature.

H e r e we examine the role of sequence alterations at the 13-kb A d h gene region in accounting for a significant increase in variance of ADH activity ob-

served after 28,200 allele generations in a D. melano- gaster mutation-accumulation experiment. While a level of A D H activity variation equivalent to that seen

for a n allozyme class in nature is observed, no evi- dence of transposable elements or other variants were found in the 13-kb A d h region.

MATERIALS AND METHODS

Mutation accumulation lines: Two sets of 500 lines of D. melanogaster had been established by T. MUKAI that were heterozygous for a second chromosome balancer (SMl marked by Cy) and a chromosome carrying a recessive lethal from a single heterozygous female (see MUKAI and COCK-

ERHAM 1977). One set is referred to as JH lines and the

other AW referring to their chromosomes of origin. To

avoid contamination, these lines were constructed as a re- cessive lethal-bearing chromosome balanced by the S M I chromosome marked by Cy and carrying a recessive lethal. After an average of 300 generations, a significant increase in genetic variation was found to have accumulated among these lines for electrophoretic mobility of enzyme coding

loci, chromosomal aberrations, visible mutants, and ADH and amylase enzyme activity (MUKAI and COCKERHAM 1977; YAMAGUCHI and MUKAI 1974; VOELKER, SCHAFFER and MUKAI 1980; SCOBIE and SCHAFFER 1982; MUKAI, HARADA and YOSHIMARU 1984; TACHIDA et al. 1989). A subset of 47 of these lines previously characterized for ADH activity was

available for molecular analysis.

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916 C. F. Aquadro et al.

somes) of all lines were replaced with that of a single homo- zygous stock, C-160, by repeated backcrosses (MUKAI, HARADA and YOSHIMARU 1984) to eliminate variation ac- cumulating at unlinked modifier loci (Adh is located at map position 50.1 and polytene bands 35B1-35B3 on chromo- some 2L). Specific activity of ADH was examined in a two- way analysis of variance with two replicates of each line (two replicates per day on two separate days). The individual activity measurements for the lines examined here are taken from the experiments of MUKAI, HARADA and YOSHIMARU (1 984) and are available upon request.

Molecular analysis of the Adh region: Genomic DNA was prepared from each line as described by BENDER, SPI- ERER and HOGNESS (1983), and digested with EcoRI and Sal1 together or with EcoRI and Hind111 together using the high and medium salt buffers, respectively, of MANIATIS, FRITSCH and SAMBROOK (1 982) and 5 mM spermidine for 2

hr at 37 O . These digests were chosen so as to divide the Adh region into a large number of readily detectable but small fragments (see Figure 1). This should allow detection of insertion/deletion variation greater than approximately 100 bp on average judging from prior experience (AQUADRO et al. 1986). Fragments were separated electrophoretically on

1.2% agarose gels using TBE buffer (MANIATIS, FRITSCH and SAMBROOK 1982), denatured and neutralized (SMITH and SUMMERS 1980) and blotted to charged nylon mem- brane (Zetabind from AMF Cuno) in 1 M ammonium ace- tate/0.05 M NaOH. The filters were prehybridized, hybrid-

ized and washed as described by the manufacturer (AMF Cuno). Nick translated probe DNA was the plasmid sASl (GOLDBERG 1980) that contains an 11.8-kb genomic frag- ment from D. melanogaster containing the Adh structural gene approximately in the center.

RESULTS

Analysis of variance for ADH activity is presented in Table 1 for the 47 lines (27 AW and 20 JH lines; listed in Table 1 footnote). As expected from the analysis of the larger number of lines presented by

MUKAI, HARADA and YOSHIMARU (1984), both sets (AW and JH) show highly significant variation among lines, while an identical analysis of 20 replicates of a single JH line showed no significant line variance (control lines of MUKAI, HARADA and YOSHIMARU

1984). T h e genetic variance component of lines is estimated to be 0.000285 f 0.000086 and 0.000524 k 0.000186 (units/mg)* for the AW and JH lines, respectively. Variation in ADH activities were contin- uously distributed with no particularly unusual variants contributing a lot to the genetic variance.

Thus the rate of accumulation of genetic variance for ADH enzyme activity is 0.000285/300 = 9.5 X

10" to 0.000524/300 = 1.75 X per generation per line. To provide perspective to the magnitude of genetic variance that has accumulated after 300 gen- erations, we can compare the accumulated variance to that observed for ADH in natural populations using the data of LAURIE-AHLBERG et al. (1980; raw data kindly provided by C . C . LAURIE). Since there is a strong bimodality of ADH activity associated with the two common allozymes (Fast us. Slow) in natural pop- ulations, we compare the mutation-line variance to

TABLE 1

Analysis of variance of specific activities of ADH in D.

melanogaster mutation-accumulation lines

Sum of

Source squares d.f. Mean square F

AW lines (1) All lines

Days 0.001974 1 0.001974 9.61**

Lines 0.034997 26 0.001346 6.55*** Interaction 0.005340 26 0.000205 0.71

Error 0.015640 54 0.000290 Total 0.057951 107

Genetic variance component of lines = 0.000285 f 0.000086 (units/mg)"

JH lines (1) All lines

Days 0.006556 1 0.005562 7.47* Lines 0.053968 19 0.002840 3.81***

Interaction 0.014147 19 0.000745 1.14 Error 0.026078 40 0.000652

Total 0.099755 79

Genetic variance component of lines = 0.000524 f 0.000186 (units/mg)'

*, **, *** Mean significant at 5.0, 1.0 and 0.5% levels. AW lines (and ADH activities): 4 (0.218), 13 (0.199), 17 (0.255), 52 (0.245), 133 (0.230), 140 (0.247), 1 5 1 (0.245), 219 (0.258), 228

(0.215), 304 (0.218), 306 (0.225), 354 (0.283), 378 (0.248), 391 (0.237), 399 (0.226), 412 (0.234), 435 (0.224), 456 (0.235), 462 (0.241). 481 (0.237), 484 (0.266), 320 X 309 (0.237), 385 X 453 (0.241), 234k (0.274), 2480 (0.246), 3470 (0.254), 4440 (0.233).

J H lines (and ADH activities): 60 (0.296), 175 (0.301), 179 (0.341), 190 (0.313), 193 (0.270), 212 (0.320) 218 (0.367), 292 (0.315), 300 (0.290), 316 (0.334), 325 (0.320), 329 (0.305), 338 (0.353), 377 (0.380), 397 (0.288), 412 (0.310). 420 (0.310), 449 (0.319), 443 X 497 (0.313), 452 X 500 (0.328).

T h e genetic variance component of lines was calculated as (MSL.~,,?

- MSI,,,,,.,,,,,,,)/4, and its standard deviation as the square root of the variance of the genetic variance component, which is (1/16)

(2(MS~,,~)'/31)

+

(1/16) (2(MS,,,,,,,,,,,.)'/31).

that of a single allozyme. Genetic variance of ADH activity in units comparable to the data of MUKAI,

HARADA and YOSHIMARU (1984) are 0.000659 and 0.000265 for 16 Fast and 31 Slow ADH allozyme lines, respectively, sampled from the eastern United States (LAURIE-AHLBERG et al. 1980). Thus, 300 gen- erations appears to be a sufficient period of time to accumulate a level of variation in activity among lines comparable to that observed in natural populations within an allozyme (Fast or Slow; Table 1).

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F I G U R E I .-Restriction n l ; l p o f the IS-kh d d h gene region es-

atnit1ed in 4 7 t ~ l l ~ l i l t i o t ~ - ~ ~ c c ~ t t l ~ ~ t l ~ ~ t i o t ~ linrs of I). rn~lanogastrr. Kc- striction sitrs arc intiic;ltctl b y t l l c lcttcr I.: for RroKI. H for l l i n t l l l l

atltl S for Soll. l'hr. n1;tsimal estrnt of thr Adh transcript (distal 1mmotrr) is shown. All lines were hetrrozygous for presence/ ;tl)sence o f tllr f:'roKI site a t posiition -4.3. N o diffcrcnccs were ol)servrtl ;ttnong or betwern the AM' and J H series lines for tlw sitrs s ~ ~ r v c y c d .

detected no evidence of any sequence alterations of any kind among the lines (including restriction site gains or losses).

DISCUSSION

N o insertions, deletions or other sequence altera- tions were observed in or around the A d h structural gene among 47 lines of

D.

melanogaster that had been allowed to accumulate mutations for approximately 300 generations. The 95% confidence interval for the rate of insertion by any element into t h e 13-kb A d h

region would thus be between 0 and 1 . 3 1 X 10"' insertions per chromosome per generation. (The up- per bound is computed as -1n(0.025)/28200, where 28200 is the total number of allele generations.) This rate is generally consistent with previous estimates of single-element rates which range from approximately 1 O-" to 10"' per element per generation (CHARLES-

WORTH and LAPID 1988; EGGLESTON. JOHNSON-

SCHLITZ and ENGELS 1988; CHARLESWORTH and

LANGLEY 1989; HARADA, YUKUHIRO and MUKAI

1990). For example, EGGLESTON, .JOHNSON-SCHLITZ

and ENGELS (1 988) scored insertion frequencies of I9

different families of transposable elements on

D.

mel- anogaster X chronlosonles by in situ hybridization. Five insertions were observed in 140 line-generations in non-P-M hybrid dysgenic crosses, and 200 insertions in 220 line-generations in dysgenic crosses. Consid- ering that the X-chromosome comprises one ninth of the total euchromatic portion of the genome

(CHARLESWORTH and LANGLEY 1989), w e can extrap-

olate that 0.321 (= 45/140) and 8.18 (= 1800/220) insertions would be expected in the total euchromatic portion of the genome i n nondysgenic and dysgenic

crosses, respectively. By comparison, our Adh data leads to an expectation of a maximum of 1.2 insertions when we extrapolate from our maximum rate of 1 .3 1

X 10"' insertions into the 13-kb region surveyed and consider that the euchromatic portion of the genome of Drosophila is approximately 1 15,000 kb ( J O H N and

MIKLOS 1988).

Given the lack of evidence of transposable element insertions in the A d h region of the mutation accumu- lation lines we examined, how can t h e significant increase in variance among lines for ADH enzymatic activity be explained? Several hypotheses can be pro- posed. First, the variation could be the result of base pair substitutions in or close to t h e A d h gene that were undetected by our restriction site map survey. Given a mutation rate of 5.58 X 10-" per base pair per generation (MUKAI and COCKERHAM 1977). the prob- ability of a mutation occurring in the 13 Kb Adh

region on any one chromosonle is (300 generations)

(5..58 X 1 0-" substitutions/bp/generation) (1 3,000 bp)

= 0.0218. Taking into account that each line repre- sents two chromosomes, the expected number of lines carrying at least one new mutation in t h e 1 3-kb A d h

region is 47(1

-

e-2(0.02'H)) = 2.0. Thus, we expect only two base substitutions over the whole region among the 47 lines, and our results would require each to be of large effect with one per set of lines

(AW and J H ) . Considering only the 765 bp that code

for A D H , the expected number of lines with substi-

tutions drops to 0.12, and clearly does not explain our data. I n addition, no mobility or null alleles at

A d h have been detected in larger analyses of this set of mutation accumulation lines including over 426,904 allele generations (VOELKER, SCHAFFER and

MUKAI 1980). Thus, the hypothesis that base pair

substitutions at or near the A d h gene account for the accumulated variance in ADH activity seems unlikely as has been argued by MUKAI, HARADA and YOSHI-

Second, transposable elements may have inserted into the Adh region and subsequently excised leaving behind small but undetectable (to our methods) alt- erations that affected expression. Only complete se- quencing of all alleles would allow a rigorous test of this hypothesis. There is certainly no evidence of such events for A d h coding sequence, a s discussed above.

A third explanation is that sequence alterations (perhaps due to base pair substitutions or transposable element insertions/deletions) in other genes could have modified the level of ADH expression or enzyme activity ("controlling factors" of MUKAI, HARADA and

YOSHIMARU 1984). I t is known that modifier loci can

influence ADH enzyme activities (reviewed by LAU-

RIE-AHLRERG 1985). However, efforts to map and

characterize these modifier loci have been unsuccess- ful due in large part to their small individual effects.

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918 C. F. Aquadro et al.

New chromosome inversions have been noted in several of these lines (YAMAGUCHI and MUKAI 1974;

T. MUKAI, unpublished results). YAMACUCHI and Mu-

KAI (19'74) found that some of the chromosome re-

arrangements shared common cytological break- points. Furthermore, the transposable element hobo

was found at the cytological breakpoints of all eleven inversions studied among 70 mutation accumulation lines by HARADA, Y U K U H I R ~ and MUKAI ( 1 990). Thus, these inversions could have been mediated by recom- bination between homologous transposable elements in nonhomologous sites in the chromosome (e.g., LIM

1988; HARADA, Y U K U H I R O ~ ~ ~ MUKAI 1990). Analysis

of our 47 lines revealed that 3 of the 27 AW lines

( 1 1 %) and 9 of 20 JH lines (45%) had new paracentric

inversions on their lethal-bearing wild second chro- mosome. None of the inversions had breakpoints im- mediately at or adjacent to Adh. Analysis of variance for lines with and without inversions (Table 2) shows a significant line effect for JH lines with inversions and not for lines without. AW lines show the reverse trend with no significant line effect for inversion lines and a highly significant line effect for lines without inversions. Overall, there is not a significantly higher genetic variance component of lines with inversions versus that for lines without inversions. T h e results from the JH lines do support the hypothesis that changes in gene expression due to modifier loci, me- diated in some cases by chromosome rearrangements, may account for some of the accumulated variance in ADH activity.

The significant result of our study is that transpos- able elements inserting and remaining in or immedi- ately flanking the structural gene are not the source of the significant increase in genetic variation for ADH enzyme activity in our mutation-accumulation lines of D. melanogaster. These conclusions corrobo- rate those of a companion study of the Amylase gene region in many of the same mutation accumulation lines (TACHIDA et al. 1989). While one 6-kb insertion was found between the duplicate amylase genes in one line, the AMY activity was not significantly altered. Surprisingly, four of 48 lines examined in that study did show replacement by double crossing over or gene conversion of the Amy genes on the Cy balancer chro- mosome by the wild chromosome. Exclusion of these lines from analysis eliminated significant between line variance in activity suggesting that the gene replace- ments were responsible for the increased variance. Subsequent analysis demonstrated that the Amy gene on the Cy chromosome had lower activity, and that its replacement in the four lines by the gene from the lethal-bearing chromosome accounted for the altered amylase activities in these lines (TACHIDA et al. 1989).

T h e Amy results suggest the possibility that similar gene conversion or double crossing over events be-

TABLE 2

Analysis of variance of specific activities of ADH in D.

melanogaster mutation-accumulation lines with and without second chromosome inversions

Sum of

Source squares d.f. Mean square F AW lines

(1) Lines with second chromosome inversions Days 0.000124 1 0.000124 1.62

Lines 0.000249 2 0.000124 1.63

Interaction 0.000153 2 0.000077 0.147 Error 0.003113 6 0.000519

Total 0.003639 1 1

Genetic variance component of lines = 0.0000 12 &

0.000009 (units/mg)'

(2) Lines without second chromosome inversions

Days 0.001865 1 0.001865 8.29** Lines 0.032868 23 0.001429 6.35** Interaction 0.005172 23 0.000225 0.86

Error 0.012527 48 0.000261

Total 0.052432 75

Genetic variance component of lines = 0.000301 2

0.000092 (units/mg)'

JH lines

(1) Lines with second chromosome inversions Days 0.003320 1 0.003320 3.53 Lines 0.038125 8 0.004766 5.07* lnteraction 0.007516 8 0.000939 1.22

Error 0.013867 18 0.000770

Total 0.062828 35

Genetic variance component of lines = 0.000957 2

0.000308 (units/mg)'

(2) Lines without inversions

Days 0.002347 1 0.002347 3.60

Lines 0.015732 10 0.001573 2.41 Interaction 0.006526 10 0.000653 1.18 Error 0.012211 22 0.000555

Total 0.036816 43

Genetic variance component of lines = 0.000230 &

0.000108 (units/mg)2

*, **, ***

Mean significant at 5.0, 1.0 and 0.5% levels. Lines with inversions (and breakpoints where data available) were as follows: AW lines: 1 7, 52 and 3470 (all 2L inversions, breakpoints not available). JH lines: 190 (28C;32D), 193 (32C;36F), 212 (2L inversion, breakpoints not available), 218 (26A;32E), 292

(32C;36E), 300 (25E;29C), 329 (32C;36E), 377 (32D;39E), 449 (52A;56D).

tween the balancer and lethal-bearing chromosomes may have contributed to the variation in ADH enzyme activity observed in the present study. T h e Cy balancer and lethal JH chromosomes carry the ADH-fast allo- zyme, while the lethal AW chromosomes carry ADH- slow (VOELKER, SCHAFFER and MUKAI 1980). Homo- zygotes for ADH-fast have, on average, ADH activities in adults that are twice the level observed in ADH- slow homozygotes (reviewed in LAURIE-AHLBERC

1985). Consistent with this difference, activities for

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Adh

4.5 site appeared to differ between the balancer and lethal bearing chromosomes (see Figure 1). All lines were heterozygous for this site indicating only that no gene exchange occurred in this region upstream of

Adh. Additional detailed restriction site or direct se- quence data will be required to critically test the contribution of gene conversion and double crossing over to the increase in genetic variance in ADH activ- ity in these mutation accumulation lines.

We thank T. BOYCE, M. GREEN and C. YOON for comments. H.T. was supported by U.S. Public Health Service grant GMll546, T.M. and K.H. were supported by Research Grants for the Ministry of Education, Science and Culture of Japan and C.F.A. was sup- ported by U.S. Public Health Service grant GM3643 1. This is paper No. 56 from the Laboratory of Population Genetics, Department of Biology, Kyushu University.

LITERATURE CITED

AQUADRO, C. F., S. F. DEESE, M. M. BLAND, C. H. LANGLEY and

C. C. LAURIE-AHLBERG, 1986 Molecular population genetics of the alcohol dehydrogenase gene region of Drosophila mela- nogaster. Genetics 1 1 4 1165-1 190.

BENDER, W., P. SPIERER and D. S. HOCNESS, 1983 Chromosomal walking and jumping to isolate DNA from the Ace and rosy loci and the bithorax complex in Drosophila melanogaster. J. Mol. Biol. 168: 17-33.

CHARLESWORTH, B., and C. H. LANGELY, 1989 The population genetics of Drosophila transposable elements. Annu. Rev. Ge- net. 23: 251-287.

DAVIS, P. S., M. W. SHEN and B. H. JUDO, 1987 Asymmetrical pairing of transposons in and proximal to the white locus of

Drosophila account for four classes of regularly occurring ex- change products. Proc. Natl. Acad. Sci. USA 84: 174-178. EGGLESTON, W. B., D. JOHNSON-SCHLITZ and W. R. ENGELS,

1988 P-M hybrid dysgenesis does not mobilize other trans- posable element families in Drosophila melanogaster. Nature

331: 368-370.

ERWIN, D. H., and J. W. VALENTINE, 1984 “Hopeful monsters,” transposons, and Metazoan radiation. Proc. Natl. Acad. Sci. USA 81: 5482-5483.

FINNEGAN, D. J., and D. H. FAWCETT, 1986 Transposable ele- ments in Drosophila melanogaster. Oxf. Surv. Eukaryotic Genes

GINZBURG, L. R., P. M. BINGHAM and S. YOO, 1984 On the theory of speciation induced by transposable elements. Genetics 107:

GOLDBERG, D. A., 1980 Isolation and partial characterization of the Drosophila alcohol dehydrogenase gene. Proc. Natl. Acad. Sci. USA 77: 5794-5798.

GOLDBERG, D. A., J. W. POSAKONY and T. MANIATIS, 1983 Correct developmental expression of a cloned alcohol dehydro- genase gene transduced into the Drosophila germ line. Cell 34:

59-73.

GOLDBERG, M. L., J. SHEEN, W . J. GEHRING and M. M. GREEN, 1983 Unequal crossing-over associated with asymmetric sy- napsis between nomadic elements in the Drosophila melanogaster

genome. Proc. Natl. Acad. Sci. USA 8 0 501 7-5021,

GREEN, M. M., 1988 Mobile DNA elementsandspontaneousgene mutation, pp. 41-50, in Banbury Report 30: Transposable Ele- ments as Mutagenic Agents. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.

HARADA, K., K. YUKUHIRO and T. MUKAI, 1990 Transposition rates of movable genetic elements in Drosophila melanogaster.

Proc. Natl. Acad. Sci. USA 87: 3248-3252.

3: 1-62.

331-334.

JOHN, G., and G. MIKLOS, 1988 The Eukaryote Genome in Deuelop- ment and Evolution. Allen 8c Unwin, London.

LAURIE-AHLBERG, C. C., 1985 Genetic variation affecting the expression of enzyme-coding genes in Drosophila: an evolutio- nary perspective. Isozymes Curr. Top. Biol. Med. Res. 12: 33- 88.

LAURIE-AHLBERG, C. C., and L. STAM, 1987 The use of P-ele- ment-mediated transformation to identify the molecular basis of naturally occurring variants affecting Adh expression in

Drosophila melanogaster. Genetics 115: 129-1 40.

LAURIE-AHLBERG, C. C., G. MARONI, G. C. BEWLEY, J. C. LUCCHFSI and B. S. WEIR, 1980 Quantitative genetic variation of en- zyme activities in natural populations of Drosophila melano- gaster. Proc. Natl. Acad. Sci. USA 7% 1073-1077.

LEWONTIN, R. C., 1974 The Genetic Basis of Evolutionary Change.

Columbia, New York.

LIM, J. K., 1988 Intrachromosomal rearrangements mediated by

hobo transposons in Drosophila melanogaster. Proc. Natl. Acad. Sci. USA 85: 9153-9157.

MACKAY, T. F. C., 1988 Transposable element-induced quanti- tative genetic variation in Drosophila, pp. 219-235, in Proceed- ings of the Second International Conference on Quantitative Ge- netics, edited by B. S. WEIR, E. J. EISEN, M. M. GOODMAN and G. NAMKOONG. Sinauer Associates, Sunderland, Mass. MANIATIS, T., E. F. FRITSCH and J. SAMBROOK, 1982 Molecular

Cloning, A Laboratory Manual. Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.

MUKAI, T., and C. C. COCKERHAM, 1977 Spontaneous mutation rates at enzyme loci in Drosophila melanogaster. Proc. Natl. Acad. Sci. USA 74: 2514-2517.

MUKAI, T., K. HARADA and H. YOSHIMARU, 1984 Spontaneous mutations modifying the activity of alcohol dehydrogenase (ADH) in Drosophila melanogaster. Genetics 1 0 6 73-84. O’HARE, K., 1987 Chromosome placticity and transposable ele-

ments in Drosophila. Trends Genet. 3: 87-88.

POSAKONY, J. W., J. A. FISCHER and T . MANIATIS, 1985 Identification of DNA sequences required for the regulation of Drosophila alcohol dehydrogenase gene expression. Cold Spring Harbor Symp. Quant. Biol. 50: 515-520.

ROSE, M. R., and W. F. DOOLITTLE, 1983 Molecular biological mechanisms of speciation. Science 2 2 0 157-162.

RUBIN, G., 1983 Dispersed repetitive DNAs in Drosophila, pp. 329-361 in Mobile Genetic Elements, edited by J. A. SHAPIRO. Academic Press, New York.

SCOBIE, N. N., and H. E. SCHAFFER, 1982 A mutator factor in a strain of Drosophila melangaster: identified by use of mutation, reversion rates and male recombination. Genetics 101: 417- 429.

SMITH, G., and M. SUMMERS, 1980 The bidirectional transfer of DNA and RNA to nitrocellulose or diazobenzyloxymethyl pa- per. Ann. Biochem. 1 0 9 123-129.

SYVANEN, M., 1984 The evolutionary implications of mobile ge- netic elements. Annu. Rev. Genet. 18: 271-293.

TACHIDA, H., K. HARADA, C. H. LANGLEY, C. F. AQUADRO, T.

YAMAZAKI, C. C. COCKERHAM and T. MUKAI, 1989 Restriction map and a-amylase activity variation among Dro- sophila mutation accumulation lines. Genet. Res. 5 4 197-203. VOELKER, R. A., H. E. SCHAFFER and T . MUKAI, 1980

Spontaneous allozyme mutations in Drosophila melanogaster:

Rate of occurrence and nature of the mutants. Genetics 9 4

961-968.

YAMAGUCHI, O., and T . MUKAI, 1974 Variation of spontaneous occurrence rates of chromosomal abberations in the second chromosome of Drosophila melanogaster. Genetics 7 8 1209-

1221.

Figure

TABLE 1
FIGURE I sitrs atnit1ed in striction atltl ;tl)sence ol)servrtl 1mmotrr) .-Restriction nl;lp of the IS-kh ddh gene region es- 47 t ~ l l ~ l i l t i o t ~ - ~ ~ c c ~ t t l ~ ~ t l ~ ~ t i o t ~  linrs of I)
TABLE 2

References

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For the purpose of this study, the teacher evaluation process included classroom evaluations using the Rubric for Evaluating North Carolina Teachers and how first-year teachers

Knowledge sharing culture plays very important role in the successful implementation of Knowledge Management in any organization. A study has been conducted to explore the current

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