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At least 19 recordsLinked to original sources
PubMed1975

Conditions for the existence of clines.

A very general partial differential equation in space and time satisfied by the gene frequency in a monoecious population distributed continuously over an arbitrary habitat is derived. The treatment is restricted to a single diallelic locus in the absence of mutation and random drift, and it is supposed that time is continuous, births and deaths occur at random, and migration is independent of genotype. With the further assumptions that migration is isotropic and homogeneous, the population density is constant and uniform (as permitted by the population regulation mechanism included in the formulation), and Hardy-Weinberg proportions obtain locally, this partial differential equation reduces to the simplest multidimensional generalization of the classical Fisher-Haldane cline model. The efficacy of migration and selection in maintaining genetic variability at equilibrium in this model is investigated by deducing conditions for the existence of clines under various circumstances. The effects of the degree of dominance, a neutral belt between the regions where a particular allele is advantageous and deleterious, finiteness of the habitat, and habitat dimensionality are evaluated. Provided at least one of the alleles is favored only in a finite region, excluding the special case in which its total effective selective coefficient is zero, if conditions for supporting a cline are too unfavorable because migration is too strong, selection is too weak, or both, a cline cannot exist at all. Thus, unless there is overdominance, the population must be monomorphic. It is possible for a cline which can barely exist under the prevailing ecological circumstances to show a large amount of variation in gene frequency.

Alleles↗
PubMed1991

A hybrid zone comprising staggered chromosomal clines in the house mouse (Mus musculus domesticus).

In the vicinity of John o'Groats (Caithness, Scotland) there is a small karyotypic race of the house mouse (Mus musculus domesticus) characterized by a diploid number of 32 chromosomes, including the metacentrics 4.10, 9.12, 6.13 and 11.14. This race forms a hybrid zone with the standard British race (fully acrocentric chromosomes, 2n = 40). Although hybrid zones normally consist of several (or many) narrow character clines at the same position, this zone is unusual in that the chromosomal clines do not coincide. The cline for arm combination 11.14 is staggered relative to the 6.13 cline and both are separate from the clines for 4.10 and 9.12 (which may or may not coincide). A variety of explanations for the structure of the hybrid zone are discussed. It is possible that this may be a case of 'zonal raciation'.

Animals↗
PubMed1991

The amplitude of circadian oscillations: temperature dependence, latitudinal clines, and the photoperiodic time measurement.

This paper develops several propositions concerning the lability of the amplitude of Drosophila circadian pacemakers. The first is that the amplitude of the pacemaker's motion, unlike its period, is markedly temperature-dependent. The second is that latitudinal variation in pacemaker amplitude (higher in the north) is responsible for two very different sets of observations on Drosophila circadian systems at successively higher latitudes. One of these is a cline in D. auraria's phase-shifting response to light, which steadily weakens in a succession of more northerly strains. The other, concerning D. littoralis in the very far north, is a cline in the rate at which eclosion activity becomes arrhythmic (the circadian rhythm damps out) in constant darkness; damping is faster in the north. The third proposition concerns a plausible selection pressure for the cline in pacemaker amplitude that we propose underlies the two directly observed clines. Two points are emphasized: (1) The amplitude of the pacemaker's daily oscillation declines as the duration of the entraining light pulse (photoperiod) is increased; and (2) the duration of the daily photoperiods throughout the breeding season is steadily increased as one moves toward the poles. Selection for conservation of pacemaker amplitude (during the breeding season) would produce the latitudinal cline we propose. The fourth, and final proposition is that since the amplitude of the pacemaker's daily motion responds systematically to change in photoperiod, amplitude is clearly one way--and a temperature-dependent way--in which insect circadian systems may sense seasonal change. These propositions concerning the temperature and latitude dependence of pacemaker amplitude may be relevant to a wider array of circadian pacemakers than Drosophila.

Animals↗
PubMed1975

Genetic drift in clines which are maintained by migration and natural selection.

Genetic drift will cause a migration-selection cline to wobble about its expected position. A rough linear approximation is developed, valid when local populations are large. This is used to calculate effects of genetic drift on clines in a stepping-stone model with abrupt and with gradual changes of selection coefficients at a single haploid locus. Among the quantities calculated are measures of slope, standardized variation of gene frequencies around their expected values, and correlation among neighboring populations with respect to deviations from the expected gene frequencies. These quantities appear to be primarily functions of Ns and Nm for a given pattern of selection. Computer simulation gives rough confirmation of these results. Standardized variances of gene frequencies and correlation of neighbors differ along the cline in the case of smooth changes in selection. In no case is pathological behavior of gene frequency deviations found near the boundaries of selective regions. Local behavior of gene frequences of nearby colonies is approximately predicted by a simple adaptation of the stepping-stone theory of Kimura and Weiss. Approximate measures of the lateral variation of the midpoint of a cline and the probability of non-monotonicity are also calculated and discussed.

Gene Frequency↗
PubMed1976

The genetic structure of a tribal population, the Yanomama Indians. XIV. Clines and their interpretation.

The Yanomama Indians are a South American tribe distributed over an irregular area approximately 200 X 300 miles. The gene frequencies observed at 12 loci in 47 villages within this area have been analyzed for the occurrence of clines. Apparently significant clines are observed for alleles of the Rh, MNSs, Kidd, Gm, Inv and serum albumin system. Available data concerning recent tribal expansion and admixture permit a tentative analysis of the causes of these clines. Although the action of selection cannot be rigorously excluded, it seems unlikely to be the major couse. Admixture with surrounding tribes plays a role which can be quantified because of the fortuitous cicumstance of two genetic markers for admixture. It is suggested that an important factor in the origin of these clines is the manner in which the tribe has recently expanded through successive village fissionings and a predominantly centrifugal pattern of village migration.

Alleles↗
PubMedDate not supplied

New studies of the alcohol dehydrogenase cline in D. melanogaster from Mexico.

An altitudinal cline of frequencies of alcohol dehydrogenase alleles occurs in D. melanogaster populations of southeastern Mexico. A similar cline of two aldehyde oxidase alleles is present, but frequencies of esterase-6 alleles are not distributed clinically. Collections were made from small dispersed populations. Some gene flow occurred throughout the lowlands according to the distribution of two moderately endemic autosomal inversions and five previously described inversions. The clines are believed dependent on a limited gene flow between temperature races of D. melanogaster.

Alcohol Oxidoreductases↗
PubMed1975

Clines in the colour polymorphism of Philaenus spumarius in Eastern Central Europe.

Populations of Philaemus spumarius (Homoptera) have been investigated in the Baltic States of the USSR, in Czechoslovakia and in Hungary. Colour morph frequencies in these highly polymorphic populations are compared with those reported earlier from northern Italy. Gradual changes in allele frequencies (clines) transect the study area, which lies in the most central part of the range of Philaenus in Europe. From north to south the allele pM increases, but pO decreases, in frequency. In their distribution, some of the other alleles also showed regional gradients. The possibility that visual selection varies regionally is dismissed on indirect grounds. Gradients in climatic severity, or in other environmental variables changing concomitantly with climate, are regarded as the primary cause of the observed clines and other differences between regions.

Alleles↗
PubMed1975

Genetic drift in a cline.

A model is developed of genetic drift in a cline maintained by spatially varying natural selection and local dispersal of individuals. The model is analyzed by an approximation scheme which is valid for weak selection and small migration rates. The results, which are based on numerical iterations of the approximate equations, are that the cline is less steep than predicted on the basis of the deterministic theory but that for weak selection the correlation between random fluctuations in neighboring colonies is approximately the same as in models of migration and drift in the absence of selection.

Biological Evolution↗
PubMedDate not supplied

Further evidence for latitudinal inversion clines in natural populations of Drosophila melanogaster from India.

Chromosomal analysis of eight Indian natural populations (six from north India and two from south India) of Drosophila melanogaster revealed the presence of 13 paracentric inversions, including one in the X chromosome. All four types of inversions--common cosmopolitan (4), rare cosmopolitan (3), recurrent endemic (2), and unique endemic (4)--were detected. The frequency of commonly occurring inversions and the level of inversion heterozygosity were found to be higher in the two southern populations. The south Indian populations are genetically more differentiated than those from the north. Also, latitudinal clines in the frequencies of the four common cosmopolitan inversions were detected. These results provide further evidence for the existence of inversion clines in Indian populations of D. melanogaster.

Animals↗
PubMed1975

A second look at some data on a cline.

The release-recapture data given in table 1 of Kettlewell et al.'s (1969) paper on a cline in the frequencies of the typica and edda morphs of the moth. Amathes glareosa have been re-analysed. Estimates of daily survival probabilities have been calculated and these have been "explained" in terms of differences between localities of release and the morph involved. The conclusions of Kettlewell et al. (1969) with regard to the survival of the moths have not been confirmed.

Animals↗
PubMed1991

Genetic differentiation and inversion clines in Indian natural populations of Drosophila melanogaster.

To study the genetic differentiation and inversion clines in Indian natural populations of Drosophila melanogaster, 14 natural populations (6 from the north and 8 from the south) were screened for chromosome inversions. The chromosomal analysis revealed the presence of 23 paracentric inversions, which include 4 common cosmopolitan, 4 rare cosmopolitan, 2 recurrent endemic, and 13 unique endemic (new inversions detected for the first time) inversions. The difference in karyotype frequencies between populations from the north and south were highly significant and the level of inversion heterozygosity was higher in populations from the south. Statistically significant negative correlations were found between each of the four common cosmopolitan inversions and latitude. These findings are in accord with results from other worldwide geographic regions and show that Indian populations of D. melanogaster have undergone considerable genetic differentiation at the level of inversion polymorphism.

Animals↗
PubMed1991

Allele frequencies of human complement factor I in a sample from Iwate, northern Japan, with the description of geographical cline.

Serum samples from 270 healthy blood donors of Iwate prefecture, northern Japan, were examined for polymorphism of factor I (IF) by using polyacrylamide gel isoelectric focusing followed by semidry horizontal electroblotting with enzyme immunoassay. In 270 individuals four different patterns were observed, and these were controlled by two common alleles, IF*A and IF*B, and one rare allele, IF*A2. Allele frequencies were estimated to be 0.1019, 0.8963 and 0.0018 for IF*A, IF*B and IF*A2, respectively. The data of IF allele frequencies thus far reported in Japan excluding Okinawa Island were compared, and a statistically significant (p less than 0.01) geographical cline was detected for IF*A and IF*B alleles.

Alleles↗
PubMed1992

The alcohol dehydrogenase polymorphism in natural populations of Drosophila melanogaster: ADH activity variation restriction site polymorphism and the Adh cline.

Alcohol dehydrogenase activity has been measured in 186 iso-second chromosome lines--104 from seven Australian populations and 82 from six Chinese populations. Restriction endonuclease variation in the Adh gene region in these lines has previously been described (Jiang & Gibson, 1991). The mean ADH activity of AdhF and AdhS lines was significantly higher in the Chinese samples than in the Australian samples. In each population on both continents the mean activity of the AdhF lines is significantly higher than that of the AdhS lines. Six lines homozygous for a thermostability variant, AdhFChD (detected in four of the Chinese populations), had intermediate levels of ADH activity and protein amount. In a subset of the lines with the highest and lowest levels of ADH, there was a correlation of 0.69 between ADH activity and ADH CRM. None of the restriction site variants was consistently associated with the amount of ADH activity. Associations between BamHI (-7.2), the Adh polymorphism and ADH activity suggest that there are modifiers of ADH 5' to the gene. The deletion (0.2) at position -2.8 on the restriction map (Jiang & Gibson, 1991) was associated with increased levels of ADH activity in AdhS lines from China. Two unique insertions in the gene region were associated with low activity in AdhF lines and a null activity allele had a deletion removing most of exon 2. A single line with a duplication of a part of the Adh coding region and of the 5' regulatory section had relatively high ADH activity. Considering all the data, the main factor affecting ADH activity levels in populations is the frequency of AdhF.

Alcohol Dehydrogenase↗
PubMed1976

Clines with variable migration.

The consequences of a discontinuity in the migration rate and of a geographical barrier in the habitat are studied in a diffusion model of migration and selection. The treatment is restricted to a single diallelic locus in a monoecious population in the absence of mutation and random drift. It is supposed further that migration is independent of genotype, the population density remains constant and uniform, and Hardy-Weinberg proportions obtain locally. It is shown that a discontinuity in the migration rate leads to a jump in the slope of the gene frequency, but not in the gene frequency itself, while a localized geographical barrier has precisely the opposite effect. These features of the gene frequency behavior are quantitatively related to the migration rate. The influence of the above inhomogeneities in migration on the maintenance of an allele in an environmental pocket is examined. The extent to which the critical condition for polymorphism is made less stringent by decreased migration outside the pocket and by a geographical barrier between the pocket and the rest of the habitat is evaluated.

Alleles↗
PubMed1992

A latitudinal cline in a Drosophila clock gene.

The clock gene period determines biological rhythmicity in Drosophila melanogaster and encodes a protein characterized by an alternating series of threonine-glycine pairs. The minisatellite region encoding the threonine-glycine repeat is polymorphic in length in natural Drosophila melanogaster populations. In this paper we report the geographical analysis of this polymorphism within Europe and North Africa. A robust clinal pattern is observed along a north-south axis. We suggest the possibility that the length polymorphism could be maintained by thermal selection because the threonine-glycine region has been shown to provide thermostability to the circadian phenotype.

Africa, Northern↗
PubMed1991

Transferrin polymorphisms in Japanese populations: north-south cline in the distribution of the TF*C2 allele.

Allele frequencies for human transferrin (TF) subtypes were determined using serum samples from Japanese subjects living in Fukui prefecture, Japan, and compared with other Japanese populations using isoelectric focusing (IEF) and immunoblotting. The application of IEF revealed considerable heterogeneity in the TF system, enhancing its potential value for anthropologic and genetic studies. So far, TF subtypes of about 27,000 Japanese individuals from 35 population groups have been analyzed to evaluate the degree of genetic variation at the TF locus. Possible geographic and biologic factors are discussed.

Alleles↗