Showing papers in "Advances in Genetics in 1954"

Comparative incompatibility in angiosperms and fungi.

Abstract: Publisher Summary Incompatibility in angiosperms is distinguished from other outbreeding mechanisms, but in fungi the distinction between separation of the sexes (dioecy) and incompatibility is a fine one. An incompatibility system is operating when all mating groups have the attributes and potentialities of both sexes. The most satisfactory method of classifying the different systems in angiosperms and fungi is by the genetic control—di-allelic or multi-allelic. With one possible exception, this division coincides with a morphological classification, heterohomomorphic in angiosperms, and with systematic orders in the fungi. The di-allelic system has developed a super gene that controls secondary characters such as morphological differences in angiosperms and nutritional or pathological characters in fungi. The di-allelic fungi with two monokaryons and one permanently heterozygous dikaryon develop a system of complementary genes—linked with the incompatibility gene—that are necessary for the dikaryon. The multi-allelic systems do not develop such secondary characters; this is a consequence of having a multiplicity of different heterozygotes.

Map construction in Neurospora crassa.

Abstract: Publisher Summary In this chapter linkage and centromere data from neurospora crassa have been compiled from all published material, as well as unpublished sources Tetrad data from gene–centromere and gene–gene intervals have been placed on a uniform basis for mapping by computing map lengths from second-division segregation frequencies and tetratype segregation frequencies, respectively Maps of the seven linkage groups have been constructed from tetrad data Seventy-five loci are shown Confidence limits are indicated for the position of each locus Two sets of maps are presented, the first is completely uncorrected for multiple crossovers and the second is corrected by means of the mapping function A few additional genes have been assigned to specific linkage groups on the basis of random isolates The use of random isolates for mapping is also discussed

Cytoplasmic inheritance in Epilobium and its theoretical significance.

Abstract: Publisher Summary This chapter leads to the hypothesis that nuclear genes and plasmon form a genetic system, which is identical with the life system of the cell. Genes and cytoplasm act upon each other, probably in opposite directions. If the balance between the two is upset, specific alterations in development arise, whose nature depends not only on the genetic properties of the genic and cytopalsmic units but also on the particular structure of the system as a whole. Gene dominance and expression can be altered by changes in the structure of the system.

The Genetics of Colias (Lepidoptera)

Abstract: Publisher Summary The Lepidoptera known cytologically are characterized by the ZO and ZW type of sex chromosomes, with the female heterogametic (ZO or ZW) and the male homogametic (ZZ). Secondary sexual characters are independent of gonadal control or hormones circulating in the hemolymph. A new bilateral gynandromorph of colias philodice is figured. The right side is female and alba and the left side is male and normal yellow except for alba patches in the distal part of the hindwing. It is suggested that these patches are produced over cells that have become femalelike by losing one Z chromosome late in development, with the entire insect presumed to have a uniform Aa or AA genotype for the alba genes. It is not known whether colias females are ZO or ZW. The chromosome number for the five species studied in this chapter is typically 31 or 32. As in Diptera, it appears that crossing over in Lepidoptera may be confined to the homogametic sex (male).

Monozygotic Twins in Cattle

Abstract: Publisher Summary Despite the fact that more than two decades have passed since Kronacher began his studies on cattle twins, no single test or series of tests yet exists through which it would be possible to distinguish between monozygotic and dizygotic cattle twins in an objective manner. However, studies on diagnostic methods have shown that the number of strongly inherited characters on which cattle twin diagnosis can be based is as great as, if not greater than, in man. Newman showed that, in man, a trained observer—after a cursory examination—was able to distinguish between monozygotic and dizygotic twins with a very great degree of certainty. Much the same situation applies to cattle. Superficially, it may seem that most cattle belonging to the same breed are so alike that they cannot be distinguished from each other (just as all people of a strange race seem indistinguishably alike), but an observer with highly developed critical faculties can easily note a great number of often subtle characteristics that make each individual different from the others.

Genetic changes in human populations, especially those due to gene flow and genetic drift.

Abstract: Publisher Summary This chapter demonstrates the application of theory—partly old, partly new—to actual field studies. This healthy movement has grown equally out of the development of theories by Wright, Fisher, Haldane, Dahlberg, Hogben, and others, on the one hand, and out of the laborious determinations of the frequencies of genetic phenotypes and the frequencies of alleles by a host of blood group analysts, physical anthropologists, and geneticists, on the other. The chapter is particularly focused on the demonstration and analysis of gene flow and genetic drift. Yet the effects of these upon the composition of populations are so inextricably knit with the effects of selection and mutation that it is impossible to discuss them altogether apart. It may be confidently expected that the development of the understanding of gene flow and genetic drift will make it possible to arrive at a better grasp of the interactions of mutation and selection with them and each other.

Artificial insemination and livestock improvement.

Abstract: Publisher Summary Artificial insemination (A.I.) has now an accepted role in the dairy industry of many countries. It has attained this position as a cheap and efficient way of getting cows in calf. The existence of large breeding groups in the A.I. centers is a magnificent opportunity for the rational use of progeny testing, in which, after finding good bulls, their successors should be bred from within the unit and progeny-tested in their turn. The exact organization of such a breeding unit still remains to be worked out, and tentative efforts are now being made in several countries. The problems that such schemes involve are often sociological and psychological, and possible solutions will have to be judged on these, as well as on genetic grounds.

The Genetics of the Newer Human Blood Factors

Abstract: Publisher Summary The terms “blood factor,” “blood group,” “antigen,” or more specifically “agglutinogen” refers to a property of the red blood cells that is produced by a gene capable of expressing itself either in single or double dose. The blood factor is demonstrable by agglutination—more rarely by hemolysis—of the red blood cells when allowed to react with a serum containing a specific antibody. This chapter presents a more detailed definition of blood factors in terms of their antibodies and a table of the better known human blood factors or antigens that determine at least nine fixed points on the chromosomes, which also gives the possible number of combinations of both genotypes and phenotypes.