A method for the estimation of gene flow parameters from a population structure caused by restricted gene flow and genetic drift

Summary A method has been developed which enables the estimation of the plant gene flow parameters _p (pollen dispersal), _s (seed dispersal) and t (outcrossing rate) from a selection-free continuously structured population in equilibrium. The method uses Wright's F-coefficients and introduces a new F-function which describes the genetic similarity as a function of the spatial distance. The method has been elaborated for wind pollinated plant species but can be modified for insect pollination and for animal species. In practice allozymes will provide for the necessary neutral genetic variation. The more loci used and the more intermediate the gene frequencies, the more reliable the results. For the estimation of _p and t together (when the outcrossing rate is not known) at least two chromosomally unlinked loci are required. The method for estimating _s depends on whether the plant species is annual or perennial. The mechanism of selfing has been analysed by the explanation of the value of t by three components: population density (d), pollen flow (_p) and relative fertilization potential of own pollen (Z). The concepts of neighbourhood size and isolation by distance, developed by Wright, who used a single gene flow parameter , have been extended to the situation which is realistic for seed plants, using all three parameters _p, _s and t. When _p is large with respect to _s, _s largely determines the value of the neighbourhood size, whereas _p is the most dominating factor in isolation by distance. The use of local effective population size and mean gene transport per generation instead of neighbourhood size and neighbourhood area, respectively, is proposed to avoid confusion. Computer simulations have been carried out to check the validity and the reliability of the method. Populations of 200 plants, using two or three loci with intermediate allele frequencies, gave good results in the calculation of _p with known value of t and of _s and N_e. With unknown t, especially with lower values of t, larger populations of at least 1,000 plants are necessary to obtain reasonably accurate results for _p and mean gene transport per generation M.Grassland Species Research Group Publication No. 81     

Chromosomal location of isozyme and seed storage protein genes in Dasypyrum villosum (L.) Candargy

Summary The zymogram phenotypes of glucose-phosphate isomerase (GPI), alcohol dehydrogenase-1 (ADH-1), glutamate oxaloacetate transaminase (GOT), superoxide dismutase (SOD), lipoxygenase (LPX), esterase (EST) and the banding patterns of gliadin and glutenin seed storage proteins were determined for Triticum aestivum cv. Chinese Spring (CS), Dasypyrum villosum, the octoploid amphiploid T. aestivum cv. Chinese Spring D. villosum (CS × v) (2n=8x=56; AABBDDVV), and for five CS-D. villosum disomic addition lines. The genes Gpi-V1, Adh-V1, Got-V2, and Sod-V2 coding for GPI-1, ADH-1, GOT-2, and SOD-2 isozymes were located in D. villosum on chromosome 1V, 4V, 6V, and 7V, respectively. Genes coding for gliadin- and glutenin-like subunits are located in D. villosum chromosomes 1V. There are no direct evidence for chromosomal location of genes coding for GOT-3, EST-1 and LPX-2 isozymes. The linkage between genes coding for glutenin-like proteins and GPI-1 isozymes in chromosome 1V is evidence of homoeology between chromosome 1V and the chromosomes of homoeologous group 1 in wheat.Research supported by the National Research Council (Italy) and National Science Foundation (USA). International cooperative project, Grant No. 85.01504.06 (CNR)     

Directional fixation of mutations in vertebrate evolution

Summary We have made pairwise comparisons between the coding sequences of 21 genes from coldblooded vertebrates and 41 homologous sequences from warm-blooded vertebrates. In the case of 12 genes, GC levels were higher, especially in third codon positions, in warm-blooded vertebrates compared to cold-blooded vertebrates. Six genes showed no remarkable difference in GC level and three showed a lower level. In the first case, higher GC levels appear to be due to a directional fixation of mutations, presumably under the influence of body temperature (see Bernardi and Bernardi 1986b). These GC-richer genes of warm-blooded vertebrates were located, in all cases studied, in isochores higher in GC than those comprising the homologous genes of cold-blooded vertebrates. In the third case, increases appear to be due to a limited formation of GC-rich isochores which took place in some cold-blooded vertebrates after the divergence of warm-blooded vertebrates. The directional changes in the GC content of coding sequences and the evolutionary conservation of both increased and unchanged GC levels are in keeping with the existence of compositional constraints on the genome.     

Enzyme-coding genes as molecular clocks: The molecular evolution of animal alpha-amylases

Summary We constructed a cDNA library for the beetle,Tribolium castaneum. This library was screened using a cloned amylase gene fromDrosophila melanogaster as a molecular probe. Beetle amylase cDNA clones were isolated from this bank, and the nucleotide sequence was obtained for a cDNA clone with a coding capacity for 228 amino acids. Both the nucleotide sequence and predicted amino acid sequence were compared to our recent results forD. melanogaster alpha-amylases, along with published sequences for other alpha-amylases. The results show that animal alpha-amylases are highly conserved over their entire length. A borader comparison, which includes plant and microbial alpha-amylase sequences, indicates that parts of the gene are conserved between prokaryotes, plants, and animals. We discuss the potential importance of this and other enzyme-coding genes for the construction of molecular phylogenies and for the study of the general question of molecular clocks in evolution.     

The kell system in Senegal: phenotype and gene frequencies

The Kell gene frequencies, determined in Senegal are as follows: Our data enter the limits already known for black African populations.     

Three distinct regulatory elements comprise the upstream promoter region of the nopaline synthase gene

Summary Fine deletion mutants were generated in the upstream control region of the nopaline synthase (nos) promoter to define the position and role of upstream regulatory elements. The results indicated that the 8 bp sequence (CAGAAACC) at -106/-113 and its inverted repeat (GGTTTCTG) at -140/-147 are important for promoter function. The downstream element appears more important than the upstream element since deletion of the former reduced promoter activity more significantly than deletion of the latter. Deletion of the element alone, however, did not abolish promoter function, whereas, deletion of the 10 bp potential Z-DNA-forming (Z) element located between the repeat elements nullified promoter activity. Therefore, it appears that the Z element is an essential upstream regulator and the repeated elements are upstream modulators of the nos promoter. These elements are functionally distinct since alteration of stereospecificity or insertion of short oligonucleotides between the elements did not significantly influence promoter activity. These regulatory elements were unable to function from 200 bp upstream of the CCAAT-TATA box region.     

A functional analysis of the repeated methionine initiator tRNA genes (IMT) in yeast

Summary Standard laboratory yeast strains have from four to five genes encoding the methionine initiator tRNA (IMT). Strain S288C has four IMT genes with identical coding sequences that are colinear with the RNA sequence of tRNA _I ^Met . Each of the four IMT genes from strain S288C is located on a different chromosome. A fifth IMT gene with the same coding sequence is present in strain A364A but not in S288C. By making combinations of null alleles in strain S288C, we show that each of the four IMT genes is functional and that tRNA _I ^Met is not limiting in yeast strains with three or more intact genes. Strains containing a single IMT2, 3 or 4 gene grow only after amplification of the remaining IMT gene. Strains with only the IMT1 gene intact are viable but grow extremely slowly; normal growth is restored by the addition of another IMT gene by transformation, providing a direct test for IMT function.Abbreviations IMT and imt (imt=initiator methionine tRNA), designate the genotype of the wild-type and the mutant alleles respectively, of the initiator methionine transfer RNA gene - met-tRNA _I ^Met methionylated initiator methionine transfer RNA - eIF-2 eukaryotic initiation factor two - GTP guanosine 5-triphosphate The calculation of Td values (the temperature at which half of the duplex is dissociated) for oligonucleotides used as probes in hybridizations was based on the assumption that the increase in Td value was 4° C for each G:C base pair and 2° C for each A:T base pair (Wallace et al. 1981)     

Genetic characterization of the mei-41 locus in Drosophila melanogaster

Summary The mutagen-sensitive mutant mus(1)104 ^D1 of Drosophila melanogaster maps to a position on the X chromosome very close to the meiotic mutant mei-41 ^D5 . Both mutants have been characterized as mutagen-sensitive and defective in post-replication repair. In the present report we show by complementation studies that mus(1)104 and mus(1)103 are allelic with mei-41. In addition, two reported alleles of mus(1)104 lie between the mei-41 alleles A10 and D5. The size of the mei-41 locus is estimated to be about 0.1 centimorgans (cM). Because several alleles of mei-41 have been shown to reduce recombination and increase meiotic chromosome loss and nondisjunction, mus(1)104 ^D1 females were examined for defects in meiosis. Although there was no evidence for reduced recombination on the second chromosome in homozygous mus(1)104 ^D1 females, heterozygous mus(1)104 ^D1 /mei-41 ^>D5 and mus(1)104 ^D1 /deficiency females showed reduced levels of recombination. However, there was no evidence of an increase in nondijunction in these females.We dedicate this article to the memory of Larry Sandler, who passed away suddenly on February 7, 1987