A NEW TYPE OF LETHAL HEREDITARY FACTOR 
 IN DROSOPHILA 
 
 BY 
 
 DAVID HIRAM THOMPSON 
 B. S. Purdue University 
 1919 
 
 THESIS 
 
 Submitted in Partial Fulfillment of the Requirements for the 
 
 Degree of 
 
 MASTER OF SCIENCE 
 IN ZOOLOGY 
 
 IN 
 
 THE GRADUATE SCHOOL 
 
 OF THE 
 
 UNIVERSITY OF ILLINOIS 
 
 1921 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
\°tl\ 
 
 -T'11 
 
 UNIVERSITY OF ILLINOIS 
 
 THE GRADUATE SCHOOL 
 
 May , 20 
 
 
 § 
 
 I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY 
 SUPERVISION ry David Hiram Thompson 
 
 ENTITLED AJEQ5W TYPE 0? LETHAL HWRTTTARY PAOTOR 
 
 IK DROSOPHILA 
 
 BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR 
 
 THE DEGREE OF Master of Science in ?nAir, g y 
 
 2 , 
 
 in Charge of Thesis 
 
 eacrof Department 
 
 Recommendation concurred in* 
 
 Committee 
 
 on 
 
 Final Examination* 
 
 Required for doctor s degree but not for master’ 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A HEW TYPE OP LETHAL HEREDITARY FACTOR IE DROSOPHILA 
 
 Contents 
 
 Page 
 
 I Introduction X 
 
 II Method of culture and maintenance of stock,, 2 
 
 III Origin of erect 
 
 IV Sex ratios and frequency of erect .......... .4 
 
 V Location of erect factor .....9 
 
 VI Discussion .,,,.11 
 
 VII Summary, X8 
 

 Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/newtypeoflethalhOOthom 
 
1 
 
 I INTRODUCTION 
 
 The question of the viability of females homozygous for 
 sex -linked lethals was raised by Morgan and Bridges (1916). 
 
 At that time they were unable to state definitely that a 
 female with such a germinal constitution would not live but 
 they made that assumption. A sex -linked lethal has been found 
 in which the lethal bearing males live to transmit the lethal 
 factor. This has made it possible to test the case and their 
 assumption was found to be correct. 
 
 About two years ago there appeared in a cross between a 
 wild female and a white ultra-bar several males which bore 
 a new sex-linked character. In this character the wings are 
 held erect over the back, the second pair of legs is function- 
 less, and on the whole, these males resemble flies which have 
 been o vex-* -etherized . When females heterozygous for this char- 
 acter are mated with erect males there appear in the next 
 generation about equal numbers of erect sons, normal sons and 
 normal -appearing females. But there are no erect females. 
 Moreover none of these females have been found to be homozygous 
 for the character and the sex ratio of two males to one female 
 is always obtained in such a cross. 
 
 The sex ratio is of interest because it is the reverse 
 of the sex ratio found in other sex-linked lethals. It also 
 suggests the lethal (l gd ) described by Miss Stark, in which 
 the lethal bearing males occasionally emerged and lived for 
 a short time, although they were unable to use their legs for 
 walking. The present lethal is similiar in that the lethal 
 

"bearing males emerge and the legs are often useless. However 
 in this case the lethal hearing males live to propagate and 
 if mated with females heterozygous for erect the lethal effect 
 
 is obtained in one half of the females. 
 
 £ 
 
 II METHOD OF CULTURE AND MAINTENANCE OF STOCK 
 
 The flies have been reared by the ordinary method and 
 kept in a room with a controlled temperature of 24 C. When it 
 is desired to examine the flies they are very lightly etherized 
 and the erect flies quickly separated from the non-erects, 
 after which they may be more heavily etherized. This precaution 
 is taken in order to avoid confusion of erect-winged flies with 
 over-etherized flies. This method of separation and classific- 
 ation of erect-winged flies is effective since no fly has been 
 found with normal wings when under the influence of ether which 
 later showed erect wings and conversely no fly classified as 
 having erect wings has later shown the normal wing posture. In 
 matings involving erect the offspring should be shaken out and 
 classified each day if close approximations to expected ratios 
 are desired, since any flies which may die ,due to crowding, 
 cannot be classified. Classifications are made under the low 
 power of a binocular microscope although they can be made equal- 
 ly well with the naked eye. 
 
 A stock pure for erect is not possible due to the total 
 absence of females homozygous for erect. A stock of erect has 
 been maintained by mating females heterozygous for erect with 
 erect males in each generation. In such a mating one always 
 gets one half erect sons and one half normal sons and a sex 
 ratio of two males to one female. The stock has been examined 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 « 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
in each generation for any marked deviation in the one to two ^ 
 sex ratio and in the percentage of erect males. A close watch 
 has been made for homozygous females. 
 
 Ill ORIGIN OP PRPCT ! 
 
 On September P, 1919, in a. cross between a wild female and J 
 a white ultra bar male there were noticed several males crawl- 
 ing about the bottle with wings erect over the thorax as in 
 over-etherized flies. This day’s count of offspring consisted 
 of 35 normal -winged females, 10 normal -winged males and 14 
 erect males. This female evidently was heterozygous for erect and 
 since she was a virgin picked from a wild stock the character 
 derived from her cannot be said to have arisen by hybridization 
 of two stocks but from a pure wild stock. It may be of interest 
 to note in connection with Miss Stark’s work (1915) on lethals 
 from freshly caught and inbred stocks that the wild stock in 
 which this erect lethal arose had been in captivity for at least 
 three or four years. 
 
 The erect males which must have been present in earlier 
 counts of the original cross were overlooked probably because 
 they were supposed to be over-etherized flies. The resemblence 
 of these erect males to over-etherized flies is striking. 
 
 In the character ’’erect" it is the raesothorax which seems 
 to be affected most because the wings are held erect over the 
 back and the second pair of legs is usually doubled up beneath 
 the body or else dragged along behind (figure 1). The wings 
 stand at right angles with the main axis of the body and they 
 usually are about parallel but occasionally touch or form an j 
 
 acute angle. The wings come into position as they expand and 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
4 
 
 remain so throughout the life of the fly, thus making flight 
 impossible. No males have been found that transmit the factor 
 for erect without having erect wings, and conversely no erect 
 males have been found which do not transmit the characteristic. 
 
 The second pair of legs usually are useless, for walking, as they 
 
 A 
 
 are either crossed and doubled up beneath the body or else they 
 drag as the animal walks. Such flies have much difficulty in 
 walking and occasionally become entangled in the food and die. 
 This fact probably accounts partially for th<^erects appearing 
 in somewhat fewer numbers than expected. Dead flies cannot be 
 classified as to the erect character and are discarded. All 
 figures given in this paper refer to counts of living flies. 
 Flies with these feeble legs often partially recover the use of 
 them for walking. In general flies cannot be classified by these 
 feeble legs since they are rather irregular in appearance. They 
 are part of the manif estation of the fa.ctor for erect, because 
 erect flies with normal -appearing legs were selected for several 
 generations, but the majority of the erect-winged males always 
 had feeble legs. With moderate care in etherization erect is a 
 readily recognized sex-linked character which is always definite 
 
 in'jits behavMfr. 
 
 A 
 
 IV SEX RATIOS AND FREQUENCY OF ERECT 
 When females heterozygous for erect are out-crossed to non- 
 erect males the usual 1:1 sex ratio is obtained and there is 
 an approximation to equality of erect and normal males. The 
 totals of such crosses are given in table 1. The scarcity of 
 erect males here is partially accounted for by the number which 
 died before they were counted, as the offspring were not removed 
 daily in every case. 
 

 
 
 
 
 
 
 « 
 
 
 
 
TABLE 1 Heterozygous female X non-erect male. 
 
 
 Normal $9 
 
 Erect dW 
 
 Normal eft? 
 
 Total 
 
 1252 
 
 573 
 
 749 
 
 Percentage 
 
 48,5 
 
 22.3 
 
 29.1 
 
 Sex Ratio 
 
 1 : 
 
 1.06 
 
 
6 
 
 If females heterozygous for erect he mated to erect males 
 the characteristic sex ratio of 1:2 is obtained and there are 
 again nearly equal numbers of erect and normal males. The totals 
 of these matings are given in table 2. It can be seen there that 
 tne results indicated by the totals are not the averages of wide- 
 ly varying . ratios , for a close approximation to the expected 
 ratio has been obtained in almost every mating. 
 

 
 
 
 . pi v/ ji»<? .8 
 
 * 
 
 - 
 
 
 
 
 
 
 
 
 
 
 
 
TABUS 
 
 2 Heterozygous 
 
 female X 
 
 erect male. 
 
 Culture 
 
 number Erect 9$ 
 
 1'Iormal 
 
 o$> Erect 
 
 oc? Normal 
 
 76,1 
 
 0 
 
 102 
 
 101 
 
 116 
 
 84.1 
 
 0 
 
 30 
 
 21 
 
 30 
 
 88.1 
 
 0 
 
 111 
 
 104 
 
 131 
 
 86.1 
 
 0 
 
 52 
 
 65 
 
 64 
 
 90.1 
 
 0 
 
 80 
 
 110 
 
 114 
 
 92.1 
 
 0 
 
 99 
 
 110 
 
 10 5 
 
 94.1 
 
 0 
 
 12 
 
 15 
 
 9 
 
 96.1 
 
 0 
 
 4 
 
 3 
 
 3 
 
 98.1 
 
 0 
 
 60 
 
 54 
 
 64 
 
 100.1 
 
 0 
 
 52 
 
 35 
 
 48 
 
 172.0 
 
 0 
 
 60 
 
 55 
 
 82 
 
 172.1 
 
 0 
 
 90 
 
 86 
 
 87 
 
 172.2 
 
 0 
 
 66 
 
 94 
 
 93 
 
 172.3 
 
 0 
 
 91 
 
 85 
 
 120 
 
 172.4 
 
 0 
 
 46 
 
 45 
 
 36 
 
 172.5 
 
 0 
 
 20 
 
 8 
 
 12 
 
 172.6 
 
 0 
 
 55 
 
 65 
 
 100 
 
 172.7 
 
 0 
 
 38 
 
 37 
 
 51 
 
 172.8 
 
 0 
 
 53 
 
 54 
 
 61 
 
 172.9 
 
 0 
 
 51 
 
 20 
 
 23 
 
 Total 
 
 0 
 
 1166 
 
 1167 
 
 1349 
 
 Percentage 
 
 0 
 
 31.7 
 
 31.7 
 
 36.6 
 
 Sex Ratio 
 
 
 1 
 
 : 2.16 
 
 
Unrelated non-erect females mated to erect males gave in 
 F-]_ equal numbers of normal -appearing females and males. Many of 
 these F 1 females were then tested by unrelated non-erect males 
 and all gave approximately equal numbers of erect and normal 
 sons. This test brings out its characteristic sex -linked behav- 
 /3\i/r. 
 
 Several thousand flies have been produced in crosses in- 
 volving erect, and a constant watch has been made for homozyg- 
 ous erect females which would indicate crossing-over between a 
 lethal factor and the erect factor, but no such females have 
 been observed. Since the lethal effect and the character erect 
 cannot be separated, it may be concluded that they are due to 
 the same factor. 
 
 In the second generation from a cross between white bar 
 females and erect males there appeared three females which car- 
 ried their wings erect. These upon being tested proved to be 
 heterozygous for erect but they transmitted this character of 
 erect wings to part of their daughters. Considerable work has 
 been done in testing these erect-winged females and it seems 
 to indicate a dominant factor which makes erect dominant and 
 is lethal in the homozygous condition if one erect factor is 
 present. This new factor seems to be located in the autosomes, 
 and. unlike the erect factor it is quite irregular in its mani- 
 festation since certain environmental conditions seem to be 
 necessary. This new dominating factor is similiar to erect in 
 that it cannot be fixed, at least when the erect factor is 
 present. 
 
 Homozygous erect females probably die in the egg or early 
 larval stages since no approximation of 2 $% of pupae containing 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
dead fliee has been found in crosses where they should occur, 
 and no dead larvae noticed in good cultures. 
 
 V LO CAT I OH OH ERECT FACTOR 
 
 In order to prove that this erect-winged lethal is a sex- 
 
 linked character its linkage relations with har and white have 
 "been obtained. White, "bar, normal -winged females were crossed 
 to red, full -eyed, erect males and the TV> generation produced. 
 
 The double-cross-over class was regarded as a cross-over in 
 each region. The males of this cross show the linkage relations 
 of erect with "bar and white readily and are summarized in tables 
 3 and 4. There was found to be 36.9^ of crossing -over between 
 white and erect and 19.3^ between bar and erect. These numbers 
 added give close approximation of 56.2^ to the established 
 5 6 % of crossing-over between white and bar. It seems evident 
 that the factor for erect lies between white and bar somewhere 
 near the locus 38* 
 

 
 
 
 
 
 
 
 
 - 
 
 < t • 
 
 
 
 
 
 
 
 • 
 
 
 
 » 1 
 
 • 
 
 . 
 
 
 f 
 
 
 
 
 
TABLE 3 Bar-erect crossing-over 
 
 Cross-over cftr Non -cross -ever cfd” 
 Total 227 952 
 
 Percentage 19*3 
 
 TABLE 4 White-erect crossing -over 
 
 Cross-over <fc? Non-crcss-over eft? 
 Total 238 407 
 
 Percentage 
 
 36.9 
 
1 
 
 
 
 
 
 
 
 * 
 
 - 
 
 - 
 
 
 
 
 
 
VI DISCUSSION 
 
 11 
 
 An hereditary lethal may he defined as any heritable qual- 
 ity which prevents the individual from reaching the adult stage 
 and reproducing. Lethal effects may also he thought of as includ- 
 ing those qualities which lower the viability of any race of 
 animals and may he termed racial lethal s. 
 
 The first case of an hereditary lethal factor, which is 
 quite typical, was demonstrated by Cuenot in mice. In mice there 
 is a yellow coat color which cannot he fixed, that is, a line 
 pure for yellow cannot he obtained. For instance, if a pure blaek 
 he crossed to a yellow, one half of the offspring are yellow and 
 one half are non-yellcw and it is not evident which is the domin- 
 ant character. But by further breeding experiments it is shown 
 that yellow is dominant because, if the non-yellow offspring be 
 mated together, none but non-yellows are obtained, showing that 
 they are pure for the absence of yellow. If the yellow offspring 
 be mated to the non-yellow equal numbers of the yellow and the 
 non-yellow are again obtained, which shows that yellow is domin- 
 ant, since it could have been present in the offspring only in 
 the single dose. 
 
 Since yellow is dominant one would expect that if he mated 
 yellow offspring together he would get yellows and non- yellows 
 in the ratio of 3:1 and of the composition 1YY : 2Yy : lyy, but 
 on the contrary one gets a 2:1 ratio as was established by Little 
 (191?) in large numbers of mice. Furthermore, one does not get 
 pure yellow mice since large numbers have been tested and all 
 have been found to be heterozygous for yellow. It was noticed 
 that when the yellow by yellow cross was made the litters were 
 

 
 
 
 
 
 
 
 
 < 
 
 c 
 
 
 
 
 
 
 t 
 
 
 < 
 
 
 t 
 
 
 
 ( 
 
 
 
 
smaller than normal, being about three-fourths as large* It was 
 then concluded that it was the pure yellow class of mice which 
 was for some reason missing and that whenever two gametes united, 
 each of which carried the yellow factor, the resulting zygote 
 did not come to maturity. 
 
 Embryo logical work has recently been done on the yellow mice 
 and it has been shown that when two yellow gametes unite they 
 form a living embryo which lives an apparently normal existence 
 
 up to the bias tula stage, when the embryos become implanted in 
 
 the uterine wall. At this point the two yellow factors manifest 
 themselves, the embryo does not become attached but dies, prob- 
 ably from lack of nourishment. It has also been shown that the 
 surviving yellow mice are mentally deficient. This is indicated 
 by their behavoir in mazes where their standard of performance 
 is much lower than that of normal mice. 
 
 This yellow mouse case is a simple, clean cut, and rather 
 completely understood example of how lethals act. 
 
 The great majority of known hereditary lethal factors are 
 found in the fruit fly, Drosophila, and the largest number of 
 these are sex-linked, that is, the factors are borne by the sex- 
 chromosomes. This is because all known lethal factors are recess- 
 ives, and sex-linked recessives are very easily found since one 
 half the sons of a female heterozygous for any one of them are 
 always pure for it. This follows since there are two sex-chromo- 
 somes in the female and one in the male which he always gets from 
 hi 8 mother. 
 
 All lethal factors must be recessive in their lethal effect 
 in order to be inherited because it is obvious that if they were 
 

 
 
 
 
 
 
 < 
 
 
 
 
 
13 I 
 
 dominant there would be no way of transmitting them. 
 
 The number of dominant lethals arising by mutation is un- 
 known but there are two cases known which are interesting in this 
 connection. Muller (1921) has described a sex-linked lethal which 
 is recessive under ordinary conditions of the germplasm but is a 
 dominant lethal when a certain other allelomorph for this lethal 
 factor is present. The other case is mentioned in this paper in 
 which the erect factor seems to behave as a dominant lethal when 
 two doses of the dominant accessory factor are present. 
 
 More is known of recessive than of dominant lethals. There 
 ifl a variety of these which differ in the time of producing death, 
 as well as the degree of viability. These variations seem to be 
 well illustrated by the following series which begins with the 
 most deadly of these lethals and grades down to their milder 
 forms . 
 
 1. The first lethal to be considered is a sex-linked recess- 
 ive factor reported by Miss Stark (1918). This causes the devel- 
 opment of tumors in the male larvae and kills them before they 
 pupate. Since this factor is carried by the sex-chromosomes it 
 follows the rules for sex-linked inheritance. It can only be 
 transmitted by the females, and the stock is maintained by mating 
 heterozygous females to normal males in every generation. The 
 sons of a heterozygous female should be equal in number to the 
 daughters, but since one half of the sons die as larvae, one gets 
 sons and daughters in the ratio of two daughters to one son, 
 which is the usual ratio in sex-linked lethals. 
 
 When one mates females heterozygous for the lethal to normal 
 males, all the sons that come to the mature stage are normal and 
 cannot transmit the defect. The daughters are of two classes. 
 
. 
 
 « 
 
 . 
 
 . 
 
 
 . 
 
 . 
 
 * 
 
 . 
 
 ‘ 
 
 - 
 
 
 
 
 
 
 
 , 
 
 , 
 
 . 
 
 , 
 
 
 
one half "being heterozygous for the lethal factor and the other 
 half "being pure for its absence. As a result the former females 
 will always transmit the defect to half their sons, while the 
 latter can never transmit it* The principal characteristic of 
 this lethal is that it kills one half of the males in the larval 
 stage "by the development of tumors. 
 
 2, The second case in this series was also described by 
 Miss Stark (1915). This is similiar to the first in that one 
 half of the sons of the heterozygous female were killed. However 
 no evidence of a tumor was found. The males receiving the lethal 
 factor lived through the larval stage and the early pupal stages, 
 but died either before they emerged or shortly afterwards. Those 
 that emerged could not walk, but fell over and lay on their sides, 
 since the legs did not seem to move coordinately and were not 
 strong enough to support the body. These flies died in a day or 
 two and could not be used in breeding experiments. The points of 
 interest in this lethal were that one half of the males were af- 
 fected as in the previous case, but that the effect was delayed 
 to the late pupal or young adult stages. It is also notable in 
 connection with the following that the lethal bearing males which 
 
 did emerge were very defective. 
 
 3. The next case in this series is the erect lethal describ- 
 ed in this paper. The lethal factor is transmitted to one half 
 the sons as in the two former cases, but does not have its com- 
 plete effect in them since they go through the whole life cycle 
 and emerge as adults. However, one can see the partial effect of 
 the lethal because the wings are carried erect and resemble the 
 the condition of rigor mortis. Also these flies have difficulty 
 
in walking since the second pair of legs is almost always para- 
 lyzed and is dragged along as the animal walks. However these 
 lethal hearing males live to breed which shows an advance over the 
 last case. These sons which bear the lethal, when mated to females 
 heterozygous for it should give the following types of offspring 
 in equal numbers: daughters pure for the lethal, daughters hetero- 
 zygous for the lethal, erect sons and normal sons, One does not 
 get all these classes of flies because there are no females prod*» 
 uced which are pure for the factor and therefore two males sur- 
 vive for every female. This shows that the females which get 
 two doses die early in the life cycle. This stock is kept going 
 by mating heterozygous females to erect males. 
 
 The outstanding points are that the factor does not have its 
 complete effect in the lethal bearing males, but such an effect 
 is obtained in the females homozygous for it. Here the ordinary 
 lethal sex ratio is reversed being two males to one female instead 
 of one male to two females. 
 
 4. For the next case in this series the character fused may 
 be taken and regarded as a mild lethal which although not lethal 
 to the individual is lethal to the race on account 6f the ster- 
 ility of all homozygous females. Here the lethal bearing males 
 live as in the erect case and show some lethal effects, in that 
 the ocelli are missing and the wings are somewhat abnormal. These 
 males when mated to heterozygous females give all the expected 
 classes of flies, and in this respect are different from the prev- 
 ious case. 
 
 5« The factor for rudimentary wing behaves in the same way 
 as fused except that the homozygous females occasionally lay a 
 few eggs. 
 
 I 
 

 
 
 
 
 
 
 
 
 
 
 „ 
 
 
 
 
 ; 
 
 < 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 « 
 
 
 
 
 
16 
 
 6. For the last case in the series any of the ordinary 
 sex-linked factors may he mentioned such as har eye, yellow 
 body etc. In these instances there is no lethal effect causing 
 certain whole classes of individuals to die nor is there com- 
 plete sterility as in other cases hut these stocks have a much 
 lower viability than the normal wild type of fly. 
 
 This series shows the different points in the life cycle 
 as well as the manner in which the lethals may manifest them- 
 selves. 
 
 In the evening primrose, Oenothera Lamarkiana, there are 
 several phenomena which have puzzled those who attempt to ex- 
 plain heredity on the determinate basis. Among these peculiar- 
 ities are the constant hybrids which apparently are races pure 
 for certain characters although they are really heterozygous 
 in composition, /mother interesting fact is that when two appar- 
 ently pure races are crossed there appear two and sometimes 
 four classes of F^ offspring. It has been shown by Muller (1917) 
 that these cases can be paralleled in Drosophila by the proper 
 use of lethals. 
 
 An example of constant hybrids in Drosophila is the dom- 
 inant character ’’beaded wings” which under selection became a 
 constant hybrid. The principal factor is a dominant which is 
 lethal in the double dose just like the yellow mouse case. 
 
 During selection a lethal factor appeared which was closely 
 linked to the normal allelomorph for beaded. Thus the beaded 
 stock consisted of flies heterozygous for both beaded and the 
 lethal. If B represents the beaded factor and 1 the lethal 
 factor and N their normal allelomorphs, there will be two types 
 of eggs and two types of sperm with regard to these factors 
 

 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 • 
 
 
 
 < 
 
 ( 
 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 ' 
 
 . L 
 
 
 
 
 
 
 
 
 
 
 • 
 
 
 9 
 
 
 
 
 
 
 
 
 
 
 
 
 . 
 
 
 
 
 
 
 
 , 
 
 
 
 
 
 * 
 
 
 
 < 
 
 ( 
 
 
 
 
 
 
 
 
 
ITT ♦ Neglecting crossing -over 
 
 namely NB and 
 
 there are three possible combinations of these two types of 
 eggs and sperm namely, NNBB, HEN, and 1NBN. The first class 
 dies as a result of the lethal action of two B*s and the sec- 
 ond as a result of the lethal action of the two l's while the 
 third class lives* This class which lives is of the same comp- 
 osition as that of the parents and it repeats as a pure line 
 except for occasional flies of other types produced by cross- 
 ing-over between the lethal and beaded factors* If this appar- 
 ently pure beaded stock be outcrossed to some other stock such 
 as the wild fly there will be two classes of $ 1 hybrids namely 
 one half beaded flies without the lethal factor and one half 
 normal flies heterozygous for the lethal. By crossing two diff- 
 erent constant hybrid races there will be four classes of 
 hybrids. 
 
 By making use of the idea of balanced lethals in connect- 
 ion with the erect stock one should be able to produce a stock 
 in which all the females would be normal in appearance and 
 the males all erect. This should be done by introducing an ord- 
 inary sex-linked lethal into the erect stock producing females 
 of the composition 1 • Here the ordinary lethal is 
 
 l e 
 
 represented by 1 and the erect lethal by l e . These females 
 when mated to erect males would give erect sons only, the nor- 
 mal sons being killed by the introduced lethal. The daughters 
 of this cross would be of the same composition as their mother 
 and equal in number to the erect sons. The offspring that reach 
 the adult stage are of the same composition as the parents and 
 the process would repeat itself much as a pure line. Crossing- 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
18 
 
 over would give normal males and females not bearing the introd- 
 uced lethal, the number of which would depend on the closeness 
 of the lethal factor to the erect factor or the presence of oth- 
 er factors which may affect crossing -over. This balanced lethal 
 should be of use in preserving stocks of other sex-linked lethals 
 since it would give a higher percentage of flies bearing the leth- 
 al factor than other methods. 
 
 VII SUMMARY 
 
 1. A female from an inbred wild stock has been found to be 
 heterozygous for a new sex-linked receesive character in which 
 the wings are held erect and the legs are feeble. 
 
 2. This character follows the sex-linked method of trans- 
 mission and shows linkage with bar and white eye, 
 
 3. The point of principal interest is that in mating females 
 heterozygous for the factor with erect males the homozygous 
 females which presumably would be erect do not appear and con- 
 sequently there are twice as many males as females. 
 
 4. The lethal effect and the character erect seem to be 
 manifestations of the same factor since it has not been possible 
 to separate them in the several thousand flies which have been 
 raised. 
 
 5. Erect males are so ill adapted to life under natural 
 conditions that they may be regarded as lethal -bearing males 
 which under laboratory conditions are permitted to live long 
 enough to propagate. Females receiving two of these lethal fact- 
 ors die earlier in the life cycle. This indicates a greater 
 effect of the two erect factors of the female as compared with 
 
19 
 
 a single erect factor of the male* 
 
 6. The single erect factor of a female supposedly is with- 
 out effect hut it is of interest to note that a dominant acces- 
 sory factor has appeared which makes the erect factor dominant 
 so that these females have erect wings and occasionally feeble 
 legs like the males. 
 
 7. There is some evidence which seems to indicate that two 
 doses of this accessory factor also make the lethal manifestation 
 of the erect factor dominant. This would explain the apparent 
 
 scarcity of heterozygous females and erect males in tables 1 and 
 

 
 
 . 
 
 . 
 
 
 
 
 
 . 
 
 , 
 
 
 
 . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
20 
 
 BIBLIOGRAPHY 
 
 Bridges, C.B. 1920 White ocelli - An example of a slight 
 mutant character with normal viability. Biol. Eull. 
 Yol. 28, pp. 231-236. 
 
 Little, C.C. 1917 The relation of yellow coat color and 
 black-eyed white spotting of mice in inheritance. 
 Genetics v ol. 2, pp. 433-444. 
 
 Mohr, O.L. 1919 Character changes caused by mutation of an 
 
 entire region of a chromosome in Drosophila. Genetics 
 Vol.4, pp. 275-282. 
 
 Mohr, O.L. and Sturtevant, A.H. 1919 A semi -lethal in Dros- 
 ophila funebris that causes an excess of males. Proc. 
 Soc. Exp. Biol, and Med. Vol. 16, pp. 95-96. 
 
 Morgan, T.H. and ^ridges, C.B. 1916 Sex-linked inheritance 
 in Drosophila. Carnegie Institution of Washington 
 Publications. No. 237. 
 
 Morgan, T.H. 1919 The physical basis of heredity. J.B, Lipp- 
 incott Company. Phila, 
 
 Muller, H.J. 1917 An Oenothera-like case in Drosophila. 
 
 Proc. Hat. Acad, Sci. Vol, 3, pp, 619- 626. 
 
 Muller, H.J, 1918 Genetic varibility, twin hybrids and 
 
 constant hybrids, in a case of balanced lethal factors 
 Genetics Vol, 3, pp. 422-499. 
 
 Muller, H.J. and Altenburg, E. 1919 The rate of change of 
 
 hereditary factors in Drosox>hlla. Soc. Exp. Biol, and 
 Med. Vol. 17, pp. 10-14. 
 
 Muller, H.J. 1921 A study of the character and mode of origin 
 of eighteen mutations in the X-chromoeome of Drosoph- 
 ila. Anat, Rec. Vo 1.20, pp.2!3. 
 

 
 t 
 
21 
 
 Quackenbush, L.S. 1910 Unisexual 'broods of Drosophila* 
 
 Science Vol* 32, pp* 183-185* 
 
 Rawls, Elizabeth, 1913 Sex ratios in Drosophila ampelophila* 
 Biol. Bull* Vol, 24, pp. 115-124. 
 
 Stark, Mary B. 1915 The occurrence of lethal factors in 
 
 inhred and wild stocks of Drosophila* Jour. Exp* Zccl. 
 V 0 1. 19, pp* 531-558* 
 
 Stark, Mary B. 1918 An hseeditary tumor in the fruit fly 
 Drosophila. Jour. Cane. Res. V 0 i. 3 s pp. 279-299. 
 
 Stark, Mary B. 1919 An hereditary tumor. Jour. Exp. Zool. 
 
 Vol* 27, pp. 509-529. 
 
 Zeleny, Charles 1920 A change in the bar* gene of Drosoph- 
 ila melanogaster involving further decrease in facet 
 number and increase in dominance. Jour. Exp. Zool* 
 
 Vol. 30, pp. 293-324. 
 

 
 ♦ 
 
 
 
 
 
 
 
 
 
 t 
 
 
 
 
 . 
 
 t 
 
 % 
 
 « 
 
 
 
 
 
 
Figure 1. ./In erect male* ( Sketched under 
 camera lucida while lightly etherized.)