Light and dark metabolism ofl- andd-amino acids in 5 strains ofChlorella vulgaris and 4 strains of the genusAnkistrodesmus

In the light, 2 out of the 4 newly testedChlorella vulgaris strains were found to use about as many amino acids as a source of nitrogen as the previously investigated strain Delft; the other 2C. vulgaris strains and 3 of theAnkistrodesmus strains used only a few. The 4thAnkistrodesmus strain used none.On the average,l-amino acids supported better growth thand-amino acids, butd-serine was preferred tol-serine by 3Ankistrodesmus strains.In the dark, growth was only obtained withC. vulgaris strain Delft, and only on a few of thel-amino acids,l-leucine in particular.The author is indebted to the Direction of the Academic Hospital Dijkzigt, Rotterdam and to Prof. Dr. H. Esseveld, Head of the Central Bacteriological Laboratory, Rotterdam, for providing facilities for the performance of this study.He thanks Mrs. Dr. H. J. Leijnse-Ybema for her help in making the chromatograms, and Mr. J. B. Lenstra, pharmacist, for advice in matters of organic chemistry.     

Genomic organization and chromosomal localization of three members of the UDP-N-acetylgalactosamine: polypeptide N- acetylgalactosaminyltransferase family

A homologous family of UDP- N -acetylgalactosamine: polypeptide N - acetylgalactosaminyltransferases (GalNAc-transferases) initiate O- glycosylation. These transferases share overall amino acid sequence similarities of approximately 45-50%, but segments with higher similarities of approximately 80% are found in the putative catalytic domain. Here we have characterized the genomic organization of the coding regions of three GalNAc-transferase genes and determined their chromosomal localization. The coding regions of GALNT1 , -T2 , and -T3 were found to span 11, 16, and 10 exons, respectively. Several intron/exon boundaries were conserved within the three genes. One conserved boundary was shared in a homologous C. elegans GalNAc- transferase gene. Fluorescence in situ hybridization showed that GALNT1 , -T2 , and -T3 are localized at chromosomes 18q12-q21, 1q41-q42, and 2q24-q31, respectively. These results suggest that the members of the polypeptide GalNAc-transferase family diverged early in evolution from a common ancestral gene through gene duplication.      

Protected polymorphism and evolutionary stability in pleiotropic models with trait-specific dominance

When alleles have pleiotropic effects on a number of quantitative traits, the degree of dominance between a pair of alleles can be different for each trait. Such trait-specific dominance has been studied previously in models for the maintenance of genetic variation by antagonistic effects of an allele on two fitness components. By generalizing these models to an arbitrary number of fitness components or other phenotypic traits with different degrees of dominance, I show that genetic polymorphism is generally impossible without antagonistic fitness effects of different traits and without trait-specific dominance. I also investigate dominance and pleiotropy from a more long-term evolutionary perspective, allowing for the study of general ecological scenarios, and I discuss the effects of trait-specific dominance on evolutionary stability criteria. When selection is mainly directional and only trait-specific dominance and antagonism cause the emergence of polymorphism, then these polymorphisms can be overtaken by single mutants again, such that they are probably short-lived on an evolutionary time scale. Near evolutionarily singular points where directional selection is absent, trait-specific dominance and overdominance facilitate the emergence of polymorphism and cause evolutionary divergence in some cases. An important outcome of these models is that trait-specific dominance allows for the emergence of genetic polymorphisms without a selective disadvantage for heterozygotes. This removes the scope for the evolution of assortative mate choice and affects dominance modification. Sympatric speciation by disruptive ecological selection requires this heterozygote disadvantage in order to evolve, and therefore it becomes less plausible if the emergence of genetic polymorphism usually occurs via trait-specific dominance and antagonistic effects.     

Extreme selection in humans against homeotic transformations of cervical vertebrae

Abstract Why do all mammals, except for sloths and manatees, have exactly seven cervical vertebrae? In other vertebrates and other regions, the vertebral number varies considerably. We investigated whether natural selection constrains the number of cervical vertebrae in humans. To this end, we determined the incidence of cervical ribs and other homeotic vertebral changes in radiographs of deceased human fetuses and infants, and analyzed several existing datasets on the incidence in infants and adults. Our data show that homeotic transformations that change the number of cervical vertebrae are extremely common in humans, but are strongly selected against: almost all individuals die before reproduction. Selection is most probably indirect, caused by a strong coupling of such changes with major congenital abnormalities. Changes in the number of thoracic vertebrae appear to be subject to weaker selection, in good correspondence with the weaker evolutionary constraint on these numbers. Our analysis highlights the role of prenatal selection in the conservation of our common body plan.