THE INHERITANCE OF A MACULA MUTATION 



CONCERNED WITH ELYTRAL SPOTTING 



AND LATENT TRAITS IN THE 



MALE OF BRUCIIUS. 1 



J. K. BREITENBECHER, 

 MARINE BIOLOGICAL LABORATORY, WOODS HOLE, MASS. 



A conspicuous, bilateral, three-character pattern is found on 

 each elytron of the normal wild type female. It consists of two 

 circular black spots placed one anterior and the other posterior, 

 and a thin horizontal line of white pubescence along the inner 

 edge. The elytron of the wild male is unmarked, the four black 

 spots and the two white lines being absent. This condition 

 enables the sexes to be easily distinguished and makes the wild 

 Bruchus quadrimaculatus , Fabr., sex-limited. 



In this culture, on October 3, 1922, at the University of 

 Oklahoma, there appeared a male insect bearing indistinct black 

 spots and white pubescence, a pattern similar to that of the 

 female described above although less perceptible. This mutation 

 was designated "macula." Approximately a year of inbreeding 

 and selection was required before homozygous macula cultures 

 could be assuredly separated from the wild type in which they 

 originated, because the macula female and the wild female are 

 identical in both homozygous and heterozygous cultures. The 

 difference between the unmarked wild type male and the spotted, 

 macula male was therefore the only visible criterion available 

 for these selection tests. 



The macula mutation is represented homozygously by the 

 genes, MM, and its recessive allelomorph, spotted females and 

 non-spotted males of the normal insect, homozygously by the 

 factors, mm. 



In the first test a (MM) female, homozygous for spotted males 

 and females was crossed with a normal (mm) male, homozygous 

 for non-spotted males and spotted females. The offspring from 



1 It is a pleasure to acknowledge my indebtedness to Dr. Frank R. Lillie, 

 Director, for the privilege of utilizing the many excellent facilities of the Marine 



Biological Laboratory. 



19 265 



