Mutational Mosaic Coat Patterns of the Guinea Pig.
TABLE OF CONTENTS PAGE INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 The Color Factors of Guinea Pigs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 A Somatic and Germinal Mosaic (Ccd+Cdcd). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Two Intense-dilute Mosaics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 An Agouti-black Mosaic ( A A +aa) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344 Two Intense-dilute Mosaics ( F f + j ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345 An Intense Brown-pale Brown Mosaic (Pp+pp). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347 DISCUSSIOV.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348 LITERATURE CITED.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
The developmental stages at which mutations occur in the germ tract
In the fruit-fly Drosophila melanogaster about 300 primary mutations have been found, most of which arose in cultures carried on in the laboratory. A study of the critical cases among these mutations has shown that a large majority of them originated at or very near the maturation stage; that a few occurred in the gonial cells some time prior to maturation; and that a few occurred early in the segmentation stage. The conclusion that most mutations occur at the maturation stage is based largely on the proportion of sex-linked recessives and of dominants that have been first found as a single individual. Approximately half of the sex-linked recessives have been discovered as a single male. This is a surprisingly large proportion and clearly means that in these cases the actual mutation occurred in the mother, and at, or not more than a very few cell generations before, the maturation of the egg. Those sex-linked recessives that did not first appear as a single male have in the main appeared as half the sons of a female already heterozygous for the gene. In these cases the actual mutation had occurred at some indeterminate stage one or more generations previous to the appearance of the character. There are now about 30 known dominants in Drosophila melanogaster, of which fully two-thirds were first found as single heterozygous individuals. This very large proportion of dominants appearing as single individuals means that the actual mutation has occurred very close to the final stage in the formation of the gamete—probably little if any prior to maturation. That mutations may occur in the oijgonial cells prior to maturation is proved by a few cases in which a single female has given rise to more than a single individual of a new sex-linked recessive character.
Genetics of the phenotypic evolution in sheep: a molecular look at diversity-driving genes
Background After domestication, the evolution of phenotypically-varied sheep breeds has generated rich biodiversity. This wide phenotypic variation arises as a result of hidden genomic changes that range from a single nucleotide to several thousands of nucleotides. Thus, it is of interest and significance to reveal and understand the genomic changes underlying the phenotypic variation of sheep breeds in order to drive selection towards economically important traits. Review Various traits contribute to the emergence of variation in sheep phenotypic characteristics, including coat color, horns, tail, wool, ears, udder, vertebrae, among others. The genes that determine most of these phenotypic traits have been investigated, which has generated knowledge regarding the genetic determinism of several agriculturally-relevant traits in sheep. In this review, we discuss the genomic knowledge that has emerged in the past few decades regarding the phenotypic traits in sheep, and our ultimate aim is to encourage its practical application in sheep breeding. In addition, in order to expand the current understanding of the sheep genome, we shed light on research gaps that require further investigation. Conclusions Although significant research efforts have been conducted in the past few decades, several aspects of the sheep genome remain unexplored. For the full utilization of the current knowledge of the sheep genome, a wide practical application is still required in order to boost sheep productive performance and contribute to the generation of improved sheep breeds. The accumulated knowledge on the sheep genome will help advance and strengthen sheep breeding programs to face future challenges in the sector, such as climate change, global human population growth, and the increasing demand for products of animal origin.