401

THE EFFECT OF MATERNAL AGE AND RADIATION ON THE RATE OF NON-DISJUNCTION IN

DROSOPHILA MELANOGASTER'

IKEXE A. UCHIDA, PI1.D. Deparnlle7lt of Paediatrics, University of Mn~zitoba nnd Dapart7izent of Medical Genetics, Clinicnl I7zvestigntio7z rind Raseorch Unit of T b a Children's Hospitnl, Winnipeg, Cnnndn

T h e discovery that mongolism, long known to be associated with maternal age, is caused by trisorny jmaltes it pertinent to examine again the question of maternal age and non-disjunction in other animals.

In their control series of 93,997 offspring of Drosopl?iln females aged f rom one to ten days Patterson, Brewster and Winchester (1932) found no increase in the rate ofnon-disjunction with increase in maternal age, but in the experi- mental series of 91,262 irradiated flies aged for the same period a striking cor- relation was found between maternal age and non-disjunction. Oster and lMuller (1960) also found n o difference in the frequency of non-disjunction in the progeny of newly hatched females and of females held f o r 30 days before mating. Unpublished data of Spieler (1961) also show no association wirh age.

T h e following experiment was set up t o test the effects of maternal age and, radiation on the rate of non-disjunction of the X chron~osomes of Droso- phila rnelrnognster aged f rom one to 29 days before mating.

Females h o m o z ~ g o u s fo r the vellow-body gene ( y ) , the non-disjunction ~narlter on the X chromosome, \.\;ere crossed with non-y, Plum-eyed (Pnl) males. T h c P777 marlter, located on chromosome 2, alas used to identify an)- XXY females sincc the P ~ J Z phenotype is altered by the presence of extra Y chromosomes. In addition, the irrelevant marlters, apricot eye (w"), Curly wing (Cy) , Dichaete (11) and Stubble (Sh) were involved in the cross, which was P y x d wiL'('; Cy/Pw; l l /Sh. P777 offspring were sib-mated and y, Pwz female progeny collected. Thcse females were held as virgins under crowded conditions at a-constant temperature of 20°C and aged from one to 29 days. T h e medium was alternated between storage food, consisting of sugar, water and agar only, and unyeasted cornmeal food t o discourage egg-laying.

A t the end of a particular period of aging half of the y, P772 felnales were exposed t o 1650r of gamma radiation f rom a Cobalt-60 source, at an intensity of 122.41 per minute. T h e distance from the radioactive source to the field was 85 cm. T h e rest of the flies were kept as controls and were ,handled in esactly the same way as the experimental series except for the radiation treat- ment. T h e females were then placed in separate vials with two or three Lobe ( L ) males. Rilales homozygous fo r 1." located o n chrornosornc 2, were used t o inalte certain that all offspring lvere indeed the progeny of this particular mat- ing. T h e flies werc transfcrrcd to fresh vials everv three days and fresh males \ifere added periodically until thc feinales died. if teen different series were handled in this wav.

'Aided by funds from the Hockefeller Foundation, Dominion-Provincial Health Grant and the U.S. Public Health Service RG 7950. Manuscript received June 29, 1962.

Can. J. Genet. Cytol. 4: 402-408. 1962.

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T h e niating scheme is given below:

T h e regular progeny of the F, females crossed with L k a l e s will be wild type females ( f / y ) and yellow illales ( y / Y ) ; the exceptional progeny yellow &males ( y / y / Y ) and lviid type males (+ /O) . I n order to be sure that the patroclinous illales were XO, spot fertility checlts were nlade especially in cases where more than one exceptional male was found in a single vial. In n o case n w e these flies fertile.

T h e results are given in Tzble I. A total of 79,658 flies were exanlined in thc irradiated series and 85,547 in the control. T h e ratio of exceptional flies among the irradiated and control series was 197:29, a seven-fold increase in tlic euperimental group n~hicli is obviously of significant magnitude. T h e

'I'AHI.IS I Frecl~~cncy of non-disjunction among total progeny of females accordilig to li~lrnher of days n f~c r emergence before mating

I I rraclia iccl I

Control Ila).sflies 1

aged kefore Regular 1 I

Esccptional Iieglll~ll- Esceptional mall% I I

'Total

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IRENE A. UCHIDA

IRRADIATED FLIES

CONTROLS

" - I 3 S 7 9 11 13 15 17 19 21 73 25 27 29

DL'fS FEMALES AGED BEFORE t l i l I N C .

Fig. 1. Histogram of frequency of non-disjuncrion among progeny of irradiated and conrrol fenlales according ro age ar tinrc of maring. Darn presenred in Table I.

results are presented graphically in Fig. 1. There is also a two-fold increase in the sex ratio of 11011-disjunctional progeny, though not a significant one (X" 2.1).

There is no evidence of an increased rate of non-disjunction with aging in the absence of radiation, in fact the regression coefficient is slightly negative. This is further supported when the progeny of control females are analyzed by age at the time when the eggs were laid (T,able 11, Fio-. 2) .

? In the irradiated series there is a positive correlation between the rate of

11011-disjunction and maternal age ( t = 2.71, d.f. = 13). Examination of the frequency of exceptions by brood, i.e. the progeny from eggs laid in successive three day periods after irradiation and mating, shows that the radiation effect 'had worn off after the third brood (Table 111). The data were therefore re- examined inc l~~ding only the progeny of the first three broods (Table IV,

FREQUENCY O F NON-OISJUNCTION IN

N O N - IRRADlAlED FEMALES

. 5 10 15 20 25 20 35 40 J5

4

AGE (DAYS)

Fig. 2. Graph of frequency of non-disjunction among progeny of control females according to age when eggs were laid. Data presented in Table 11.

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46

Age

16

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24

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1 2 3 4 5 6 7 8 9 10

11

12

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3262

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IREXE .4. UCHIDA

TABLE 111 Frcquc~icy of lion-disj~~nctio~l in progeny of irradiated feinales classified by the

number of days after radiation and mating The females Kere transferred to fresh food vials at 3-day intervdls.

Irradiated I Co~ltrol 1

Days after Radiation I Esccptior~al i Esccptioi~al

Regular I I I No. ! %

I a- IRRADIATED FLIES

0 . ~ 1 X- - CONTROLS

I 5 9 13 17 21 25 29

1

D A Y S FEMALESAGED BEFORE MATING

Fig. 3 . Graph of rcgrcssion of percent of exceptional progeny on number of days aged before mating. Data from Table IV, i.e., eggs laid only \vithin 9 days after mating.

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NON-DIS JUNCTION IN DROSOPHILA 407

TABLE IV Frcq~~ency of non-disjunr~ion resulling from eggs laid

within 9 clays after illati~lg

I I

I Irradiated I Colltrol Days flies

aged kcforc Regular Exceptiollal Regular Exceptional mating

n l o

Total 1 19498 1 18570 1 15 1 165 1 0.471 22876 1 21620 / 3 1 14 1 0.038 I

Regression of O/c esceptiollal

on clay

Fig. 3). T h e total rate of non-disjunction is of course higher when the later broods are omitted, but thc correlation between maternal age and ratc of non- disjunction renlains in the irradiated group.

Discussion With thc discovery of ancuploidy in certain congenital malformations

soine interest has bcen directed towards the etiology of abnormal chro~nosome division in man. Since latc maternal age appears somehon~ to be associated n,ith trisoinic conditions, a fact well established in mongolism, one nlight sup- pose that aging itself inay increase the rate of non-disjunction. T h e present experiment, together with other studies of inaternal age and non-disjunction,. offers no supporting evidcnce in Drosopkiln.

Thcre is no doubt that radiation increases the rate of non-disjunction i n D~osopkiln. This was first reported by hlavor in 1924 and has been confirmed several times. Patterson, Brewster and IVinchcster (1932) found this increase to be rclated to thc age of the eggs retained in the ovarics. However excep- tional males resulting from irradiated mature eggs could be the product of chroinosome loss rather than meiotic non-disjunction. These exceptions would presumably be found among the first few flies to emerge. I t is difficult there- fore to deterinine exactly how much of the radiation effect is on meiotic non- disjunction. T h e fcmale data however are indicative of a correlation between maternal age and non-disjunction with exposure to radiation where no such evidence cxists in the absence of radiation.

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IRENE A. UCHIDA

Summary In the absence of radiation there was no detectable effect of maternal age

on the freqi~ency of XO and XXY progeny in Drosophila ~nelmzogccster. With irradiation, honrever, there was, in addition to an overall increase, a significant effect of maternal age. Females who were older at the time of irradiation pro- duced more exceptional progeny, in agreement with earlier results of Pat- terson. Breurster and Winchester.

Acknowledgments

I am indebted to Professor James F. Crow, University of Wisconsin, for suggestions in the planning and analysis of this experiment. I ~ o u l d also like to acltnowledge the generous laboratory facilities provided by the Division of Plant Science, Department of Agriculture, Unir~ersity of Manitoba, and the constr~~ction of special apparatus with the use of the Eldorado Cobalt-60 Therapy Unit by the staff of the Manitoba Cancer Treatment and Research Foundation.

References Mavor, J. W. 1924. T h e productioll of non-disjunction by X-rays. J. Exptl. Zool. 39:

381-432. Oster, I. I., and Muller, H. J. 1960. Personal communication. Patterson, J. T., Brewster, W., and Winchester, A. M. 1932. Effects produced by aging

and X-raying eggs of Drosopbiln nzelnnognster. J. Heredity 23: 325-333. Spieler, R. A. 1961. Persolla1 communication.

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