File:Analysis of development (1955) (17982016868).jpg

Title: Analysis of development
Identifier: analysisofdevelo00will (find matches)
Year: 1955 (1950s)
Authors: Willier, Benjamin H. (Benjamin Harrison), b. 1890
Subjects: Embryology; Embryology
Publisher: Philadelphia, Saunders
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
Fig. 4L Mosaic eye of Habrobracon juglandis. Ifpper left: ivory (o*C); lower right: cantaloupe (Oc). Note the wild type coloration at the junc- tion of the two tissues and the decreasing wild type coloration within the cantaloupe region. (After A. R. Whiting, '34.) tween the narrow bar eye of Drosophila and the normal round eye is caused in a twofold way: (1) an embryonic or very early larval reduction in the size of the eye disc which may be an autonomous result of the geno- type, and (2) a later larval interference with the formation of a specific diffiisible sub- stance which is instrumental in transform- ing cells of the eye disc into ommatidia (Chevais, '43). Genie action at a distance may be brought about by substances whose transfer from one part of the body to another is mediated by a circulatory system. In some instances action at a distance results from short range diffu- sion of gene-dependent substances rather than from equal distribution of such substances throughout the body. A striking example has been described in the parasitic wasp Habro- bracon juglandis (A. Whiting, '34). (See Fig. 41.) The normal stock possesses a black eye pigment while the coloration in two non- allelic mutant stocks is ivory and cantalovipe, respectively. We may signify the phenotype black as the genotype "not-ivory, not-canta- loupe," the phenotype ivory as genotype "ivory, not-cantaloupe," and the phenotype cantaloupe as genotype "not-ivory, canta- loupe." From double nucleus eggs individ- uals have been raised which carry in one part of an eye the genetic constitution "ivory, not-cantaloupe" and in the other part "not-ivory, cantaloupe." On the whole there is autonomy of phenotypic expression as wit- nessed by a large ivory and a large canta- loupe area. However, at the border zone between the two a strip of cells is neither ivory nor cantaloupe but black. This finding can readily be explained if one assumes that a substance produced in only one of the two genetically different tissues diffuses into the other and thus reconstitvites the fvill effect of a "not-ivory, not-cantaloupe" genotype. The black zone shows a sharp border with the cantaloupe region but gradually grades over an orange coloration into the ivory part. The orange is known as an intermediate step between fvill black and ivory pigmenta- tion. From these facts and others it has been inferred that the diffusible substance is pro- duced in the "not-ivory, cantaloupe" region by the dominant not-ivory gene. An unusually interesting nonautonomous differentiation, also in mosaics of Habro- bracon, concerns the external genitalia (P. W. Whiting, Greb, and Speicher, '34; Whiting, '40). Here, eggs develop occa- sionally in which the mature egg nucleus as well as a polar nucleus take part in parthen- ogenetic cleavage. Since the diploid females
Text Appearing After Image:
Fig. 42. Ventral view of genitalia of a male com- posed of tissues of two different sex genotypes. The right outer clasper is feminized, resembling a mi- nute sensory female gonapophysis. (From P. W. Whiting, '40.) are heterozygous for a pair of genetic sex "factors," and their sons are usually hemi- zygous for either one or the other of the sex factors, the offspring developing from the binucleate eggs may be genetically mo- saic, possessing one of the sex factors in some of its nuclei and the other sex factor in

Note About Images