MISC. PUB. 1178, U.S. DEPT. OF AGRICULTURE 



genes are introduced. Each conditional lethal 

 trait may be determined by one to four genes, 

 and two or three conditional lethal traits may 

 be simultaneously introduced into the popula- 

 tion. 



Conditional lethal traits may be found in the 

 genetic variations in adaptations to climate and 



to seasonal regulations. A few examples are (1) 

 inability to diapause, (2) inappropriate dura- 

 tion of diapause, (3) inappropriate critical 

 thresholds of diapause-inducing stimuli such as 

 photoperiod, temperature, or dietary factors, (4) 

 inappropriate choice of hibernal niches, and 

 (5) inability to develop cold hardiness. 



Native Population Overflooded 

 With Release Strain Bearing Conditional Lethal Traits 



A preliminary evaluation of the potential for 

 insect population suppression by conditional 

 lethal traits was made by Klassen and others 

 (5). They considered the suppressive effect of 

 a trait determined by one, two, or three auto- 

 somal genes and by three autosomal genes plus 

 one sex-linked gene. In addition, these authors 

 calculated the suppressive effect when two or 

 three conditional lethal traits, each determined 

 by a single dominant gene, are combined in the 

 release strain. We decided to expand these cal- 

 culations and to extend them to release strains 

 with two or three conditional lethal traits. Each 

 trait was determined by one, two, three, or four 

 independent genes as follows: 



One Dominant Autosomal Gene. — The geno- 

 types that were inviable when the conditional 

 lethal trait was expressed were AA and Aa, 

 whereas aa was the only viable genotype. 



Two Autosomal Genes With Additive Effects 

 (aabb) . — In the examples computed, each of the 

 four alleles was assigned a genotypic value of 1 

 or 0. The native strain AABB had a genotypic 

 value of 4, and the release strain aabb had a 

 genotypic value of 0. We assumed that the con- 

 ditional lethal trait was expressed in individuals 

 with genotypic values of 0, 1, and 2. Therefore 

 AABB, AABb, and AaBB were the only viable 

 genotypes. 



Three Autosomal Genes With Additive Ef- 

 fects (aabbdd). — Each of the six alleles was 

 assigned a genotypic value of 1 or 0. The native 

 strain AABBDD had a genotypic value of 6, and 

 the release strain aabbdd had a genotypic value 

 of 0. We assumed that the conditional lethal 

 trait was expressed in individuals with 

 genotypic values of 0, 1, 2, and 3. Examples of 

 viable genotypes were AABBDD, AaBBDD, and 

 AABBdd. 



Four Autosomal Genes With Additive Effects 

 (aabbddee) . — Each of the eight alleles was as- 

 signed a genotypic value of 1 or 0. The native 

 strain AABBDDEE had a genotypic value of 8, 

 and the release strain aabbddee had a genotypic 

 value of 0. We assumed that the conditional 

 lethal trait was expressed in individuals with 

 genotypic values of 0, 1, 2, 3, 4, and 5. Examples 

 of viable genotypes were AABBDDEE, 

 AABBDDee, and AaBbDDEE. 



One Dominant Sex-Linked Gene and Three 

 Autosomal Genes With Additive Effects (a- 

 bbddee) . — The sex-linked allele a was assigned 

 a value of and its allele A was assigned a 

 genotypic value of 3. Since A was fully domi- 

 nant, the gene A A had a value of 3. The auto- 

 somal factors B, D, and E were each assigned a 

 value of 1, and their respective alleles b, d, and 

 e were each assigned a value of 0. We assumed 

 that the conditional lethal trait was expressed 

 in individuals with genotypic values of 0, 1, 2, 

 3, 4, and 5. Examples of viable genotypes were 

 A-BBDDEE, AABBDDEE, and a-BBDDEE. 

 The heterogametic sex (A-BBDDEE) was as- 

 sumed to be female, and the homogametic sex 

 (AABBDDEE) was assumed to be male. 



Algebraic expressions describing the segrega- 

 tion of genes that determine conditional lethal 

 traits were derived by Klassen and others (5) . 

 These authors arbitrarily assigned values or 

 "weights" to each allele so that each genotype 

 could be given a "genotypic value." In addition, 

 they arbitrarily set minimum genotypic values 

 required for survival and gave algebraic expres- 

 sions to calculate the numbers of surviving 

 genotypes in the Fi, F 2 , and F 3 generations 

 when a native population is overflooded once 

 with a release strain homozygous for the genes 



