The patterns of genetic diversity in Carpentaria acuminata (Arecaceae), and rainforest history in northern Australia

Carpentaria acuminata occurs in monsoon rainforest and is endemic to the Northern Territory, Australia. The genetic diversity of C. acuminata populations was surveyed across the geographical range of the species using isozyme analysis. Genetic diversity within C. acuminata populations ( H _E = 0.143) was typical of rainforest species and woody angiosperms generally. Genetic diversity was not correlated with rainforest patch size. However, there was significant heterogeneity among populations ( F _ST = 0.379), with infrequent effective gene flow among populations ( Nm = 0.39). Genetic diversity was negatively correlated with increasing distance between neighbouring C. acuminata populations, but geographical distance was not a good predictor of genetic similarity. C. acuminata is a favoured food of mobile frugivores such as Torres Strait pigeons and flying foxes. The decreased diversity with decreasing density of populations indicated that seed dispersal by frugivores has been important for the maintenance of diversity in this species. Populations known to have originated on relatively young, Holocene landforms were not necessarily genetically depauperate. Gene flow by pollen is apparently limited because C. acuminata populations are significantly inbred regardless of genetic diversity ( F = 0.641). The distribution and diversity of rare alleles, i.e. those occurring in few populations, is consistent with the theory of rainforest contraction during the Pleistocene.     

Long-pollen Movement and Deviation of Random Mating in a Low-density Continuous Population of a Tropical Tree Hymenaea courbaril in the Brazilian Amazon

Mating system and pollen flow are two key elements to understand the genetic structure of tree species. Mating and pollen-dispersal patterns of a low-density population of bat pollinated Hymanea courbaril were examined before logging in a 546-ha plot in the Brazilian Amazon. The multilocus genotypes of nine microsatellite loci were determined for 130 adult-trees and 367 seeds collected from 20 seed-trees. Mating system analysis, using mixed-mating model and paternity analysis showed that the studied population is perfectly outcrossed ( t_m = 1.002), and probably self-incompatible. However, significant deviations from random mating were detected for mating among relatives ( t_m − t_s = 0.096, P < 0.05) and correlated matings ( r_p = 0.289, P < 0.05), indicating inbreeding in the population and that part of offspring are full-sibs (28.9%). Inbreeding was reflected in the positive and significant fixation index observed in adult trees ( F = 0.137, P < 0.05), although no significant inbreeding was detected in offspring ( F = 0.074, P > 0.05). The effective number of pollen donors mating with each seed-tree was determined to be low ( N_ep ≈ 4). The average of pollen flow distance was measured inside of the plot by both paternity (827 ± 429 m) and TwoGener analysis (115–363 m). However, this underestimated pollen dispersal distance, since the detected rate of pollen immigration inside of the plot was high (55%). The observed long-pollen dispersal distance is probably related to pollination by bats and the low density of reproductive trees in the site.     

Glutamate Uptake Stimulates Na+,K+-ATPase Activity in Astrocytes via Activation of a Distinct Subunit Highly Sensitive to Ouabain

Abstract: The excitatory amino acid glutamate was previously shown to stimulate aerobic glycolysis in astrocytes by a mechanism involving its uptake through an Na⁺-dependent transporter. Evidence had been provided that Na⁺,K⁺-ATPase might be involved in this process. We have now measured the activity of Na⁺,K⁺-ATPase in cultured astrocytes, using ouabain-sensitive ⁸⁶Rb uptake as an index. l -Glutamate increases glial Na⁺,K⁺-ATPase activity in a concentration-dependent manner with an EC₅₀ = 67 µ M . Both l - and d -aspartate, but not d -glutamate, produce a similar response, an observation that is consistent with an uptake-related effect rather than a receptor-mediated one. Under basal conditions, concentration-dependent inhibition of Na⁺,K⁺-ATPase activity in astrocytes by ouabain indicates the presence of a single catalytic site with a low affinity for ouabain ( K _0.5 = 113 µ M ), compatible with the presence of an α₁ isozyme. On stimulation with glutamate, however, most of the increased activity is inhibited by low concentrations of ouabain ( K _0.5 = 20 n M ), thus revealing a high-affinity site akin to the α₂ isozyme. These results suggest that astrocytes possess a glutamate-sensitive isoform of Na⁺,K⁺-ATPase that can be mobilized in response to increased neuronal activity.     

Population divergence in the amphicarpic species Amphicarpaea edgeworthii Benth. (Fabaceae): microsatellite markers and leaf morphology

Comparative analyses of the genetic differentiation in microsatellite markers ( F _ST) and leaf morphology characters ( Q _ST) of Amphicarpaea edgeworthii Benth. were conducted to gain insight into the roles of random processes and natural selection in the population divergence. Simple sequence repeat analyses on 498 individuals of 19 natural populations demonstrate that a significant genetic differentiation occurs among populations (mean F _ST = 0.578), and A. edgeworthii is a highly self-fertilized species (mean selfing rate s  = 0.989). The distribution pattern of genetic diversity in this species shows that central populations possess high genetic diversity (e.g. population WL with H _E = 0.673 and population JG with H _E = 0.663), whereas peripheral ones have a low H _E as in population JD (0.011). The morphological divergence of leaf shape was estimated by the elliptical Fourier analysis on the data from 11 natural and four common garden populations. Leaf morphology analyses indicate the morphological divergence does not show strong correlation with the genetic differentiation ( R  = 0.260, P  = 0.069). By comparing the 95% confidence interval of Q _ST with that of F _ST, Q _ST values for five out of 12 quantitative traits are significantly higher than the average F _ST value over eight microsatellite loci. The comparison of F _ST and Q _ST suggests that two kinds of traits can be driven by different evolutionary forces, and the population divergence in leaf morphology is shaped by local selections.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 505–516.     

Relative contribution of contemporary pollen and seed dispersal to the effective parental size of seedling population of California valley oak (Quercus lobata, Née)

For plant populations, gene movement through pollen and seed dispersal governs the size of local genetic neighbourhoods and shapes the opportunities for natural selection and genetic drift. A critical question is how together these two processes influence the evolutionary dynamics of local populations. To assess the respective contributions of pollen and seed flow, we propose a novel indirect assessment of the separate male and female gametic contributions to total effective parental size ( N _e), based on parental correlations estimated via kinship coefficients, that can be applied to data sets that include unambiguous genotypes for male and female gametic contributions. Using the endemic Californian valley oak ( Quercus lobata ) as our study species, we apply this method to a set of microsatellite genotypes for two distinct ecological sets of naturally recruiting seedlings with acorns attached. We found that the effective numbers of contributing male parents ( N _ep) exceed effective numbers of female parents ( N _em) for seedlings established beneath adult trees ( N _ep = 8.1 and N _em = 1.1), as well as for seedlings established away from adult trees ( N _ep = 15.4 and N _em = 2.7), illustrating that seed dispersal enhances pollen dispersal and increases the effective number of seed sources in open seedling patches. The resulting effective parental size of seedling populations translates into smaller effective numbers of parents for undispersed vs. dispersed seedlings ( N _e = 3.6 and N _e = 6.7, respectively). This study introduces a novel statistic method and provides important new evidence that, on a short-term temporal scale, seed dispersal shapes the local neighbourhood size of new recruits.     

Gene markers for alcohol-metabolizing enzymes among recombinant inbred strains of mice with differential behavioural responses towards alcohol

The genetic variability of alcohol dehydrogenase (C₂ isozyme), aldehyde dehydrogenase (A₂ isozyme) and aldehyde oxidase (A₂ isozyme) has been examined among recombinant inbred strains of mice which have been previously studied concerning their differential behavioural responses towards alcohol. The results showed no correlation between biochemical phenotype for these loci and behavioural response.     

Allozyme Diversity in Populations of Cymbidium goeringii (Orchidaceae)

Abstract: Using 14 allozyme loci, we investigated levels of genetic diversity within populations, and degree of genetic divergence among 24 populations of Cymbidium goeringii (Orchidaceae) in Korea and Japan. Cymbidium goeringii maintains high levels of genetic diversity both at population (mean expected heterozygosity, H _e = 0.238) and species levels (0.260). Means of H _e found in 24 populations were not significantly different from each other. About 90 % of the total variation in the species is common to all populations (mean G _ST = 0.108). No unique allele was found in any population. The indirect estimate of gene flow based on the mean G _ST was high ( Nm = 2.06). Nei's genetic identities for pairs of populations had high values (mean = 0.974 [SD = 0.013]). The Mantel-Z test showed a significant correlation between genetic distance and geographic distance. However, the mean G _ST value between 17 populations in Korea and seven Japanese populations was relatively low (0.029), even though the land connection between the southern Korean peninsula and southern Japanese archipelagos has not existed since the middle Pleistocene. Large numbers of small seeds of C. goeringii might travel long distances by wind from populations to populations both in Korea and Japan, increasing genetic diversity within populations and maintaining low genetic differentiation among populations.     

An immunochemical analysis of the novel liver-restricted LDH activity from cichlid fishes (Cichlidae: Teleostei) confirms its non-orthology with piscine LDH-C

In an electrophoretic survey of lactate dehydrogenase (LDH) isozymes in neotropical cichlid fishes (Perciformes: Cichlidae) several species were discovered in which a cathodal liver-restricted isozyme is expressed along with the highly anodal eye-restricted isozyme (LDH-C₄) typically encountered in perciform fishes. Biochemical characterization of these two isozymes from the basketmouth cichlid, Acaronia nassa (Heckel), strongly suggested that they were non-orthologous and challenged the accepted view that eye- and liver-restricted LDH isozymes are alternative expressions of the same (LDH-C *) gene. In this study, antiserum raised against cypriniform (goldfish) liver-restricted LDH-C₄ failed to cross-react with the basketmouth liver-restricted analogue while effectively titrating the eye-restricted, anodal isozyme and, at higher titres, the LDH-B₄, heart-restricted isozyme from all cichlid species. Anti-serum raised against basketmouth muscle-restricted LDH-A₄ failed to titrate any of the eye- and liver-restricted isozymes. These data confirm the orthology of eye- and liver-restricted LDH isozymes in Cypriniform and Perciform fishes as originally proposed, suggest that the liver-restricted isozyme of cichlid fishes is non-orthologous and further raise the question of identity and evolutionary origin of this anomalous LDH activity.     

Conservation Genetics of an Endangered Herb, Hanabusaya asiatica (Campanulaceae)

Abstract: Hanabusaya asiatica (Nakai) Nakai (Campanulaceae), a bee- pollinated, perennial herb, is restricted to the mountainous regions of the eastern-central Korean peninsula. Allozyme analyses for 348 individuals assessed the levels of genetic diversity for five populations. Spatial autocorrelation statistics were also used to examine the spatial distribution of allozyme polymorphisms. The species maintains high levels of allozyme diversity ( H _eS = 0.217) and it exhibits low allozyme differentiation among populations ( G _ST = 0.132) compared with other endemics (mean H _e = 0.096, G _ST = 0.248). There is an apparent pattern of isolation by distance among populations. These results suggest that H. asiatica is at a genetic equilibrium. A considerable deficit in numbers of heterozygotes suggests mating among relatives in populations. At least three populations of H. asiatica should be sampled or conserved to capture or maintain > 99 % of the genetic diversity in the species as a whole. Within local populations, individuals are distributed in a structured, isolation by distance, manner. Approximate genetic patch width in the populations of H. asiatica examined is 5 - 8 m. For conservation purposes, it is suggested that, in general, the sampling of H. asiatica should be conducted at intervals in order to efficiently sample the genetic diversity across an entire population.     

Genetic structure within and among regional populations of the Eurasian badger (Meles meles) from Denmark and the Netherlands

The Eurasian badger Meles meles has a wide distribution area ranging from Japan to Ireland. In western Europe badger habitats are severely disturbed by anthropogenic factors, leading to fragmentation into subpopulations and formation of a metapopulation substructuring of once continuous panmictic populations. We have examined the genetic structure of Dutch and Danish badger populations on a relatively small scale (within countries) and a larger scale (between countries). The levels of genetic variation of populations were moderate and did not differ significantly among populations (overall H _O=0.30, overall H _E=0.34). Considerable genetic differentiation between the Dutch and Danish populations was found (overall F _ST=0.32, mean pairwise Dutch–Danish F _ST=0.42), indicating a large-scale substructuring of these western European badger populations. Further analysis showed that the Danish badger population can be substructured into three clusters [ P _{( k =3)}=0.99], but the Dutch populations cluster into one more or less panmictic population [ P _{( k =1)}=0.99] with little or no substructuring. The presence of migration barriers, such as roads, together with the peninsular geography of Denmark, may have led to this structuring of badger populations. In contrast, measures that improve migration and connection to other populations from neighboring countries may have prevented substructuring of the Dutch badger population.     

Experimental analysis of biparental inbreeding in a self-fertilizing plant

Abstract.— Localized dispersal and mating may genetically structure plant populations, resulting in matings among related individuals. This biparental inbreeding has significant consequences for the evolution of mating systems, yet is difficult to estimate in natural populations. We estimated biparental inbreeding in two populations of the largely self-fertilizing plant Aquilegia canadensis using standard inference as well as a novel experiment comparing apparent selfing between plants that were randomly relocated within populations to experimental control plants. Using two allozyme markers, biparental inbreeding ( b ) inferred from the difference between single-locus and multilocus estimates of selfing ( b = s_s – s_m ) was low. Less than 3% of matings involved close relatives (mean b = 0.029). In contrast, randomly relocating plants greatly reduced apparent selfing (mean s_s = 0.674) compared to control plants that had been dug up and replanted in their original locations ( s_s = 0.953, P = 0.002). Based on this difference in s_s , we estimated that approximately 30% of all matings involved close relatives (mean b = 0.279, 95% CL = 0.072–0.428). Inference from s_s – s_m underestimated b in these populations by more than an order of magnitude. Biparental inbreeding is thought to influence the evolution of self-fertilization primarily through reducing the genetic cost of outcrossing. This is unlikely to be of much significance in A. canadensis because inbreeding depression (a major cost of selfing) is much stronger than the cost of outcrossing. However, biparental inbreeding combined with strong inbreeding depression may influence selection on dispersal.     

Population genetic analyses of an amphi-Atlantic species: Lychnis alpina (Caryophyllaceae)

Lychnis alpina is a perennial caryophyllaceous plant with an amphi-Atlantic distribution. 27 populations are described on the basis of allozyme data from 11 electro-phoretic loci. L. alpina has a relatively low level of genetic variation, 3 of the loci are polymorphic ( P.,_%= 20.2%) and the mean expected heterozygosity per indivindual is H³= 0.233 the three polymorphic loci included (H = 0.064, 11 loci included). Despite relatively low level of genetic variation, the genetic diversity among populations is relatively high with F_ST= 0.51. A hierarchial analysis of genetic diversity demonstrates that most of the genetic diversity exists as interpopulational, intra-regional diversity. Genetic identity is not associated with the intercontinental geographical distribution of the populations, neither is the diversity correspondant to taxonomic relationships.     

Chloroplast DNA phylogeography of the argan tree of Morocco

Polymorphisms in the chloroplast genome of the argan tree (Sapotaceae), an endemic species of south-western Morocco, have been detected by restriction site studies of PCR-amplified fragments. A total of 12 chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) fragments were amplified and digested with a single restriction enzyme ( Hin fI). Polymorphisms were identified in six of the cpDNA fragments, whereas no mtDNA polymorphisms were detected in a survey of 95 individuals from 19 populations encompassing most of the natural range of the species. The cpDNA polymorphisms allowed the identification of 11 haplotypes. Two lineages, one in the south-east and the other in the north-west, divide the range of the argan tree into two distinct areas. The level of genetic differentiation measured at the haplotype level ( G _STc= 0.60) (i.e. with unordered haplotypes) was smaller than when phylogenetic relationships were taken into account ( N _STc= 0.71–0.74) (ordered haplotypes), indicating that population history must be considered in the study of the geographical distribution of cpDNA lineages in this species. If contrasted with the level of nuclear genetic differentiation measured in a previous study with isozymes ( G _STn= 0.25), the results indicate a relatively high level of gene flow by seeds, or conversely a relatively low level of gene flow by pollen, as compared with other tree species. Goats and camels could have played an important role in disseminating the fruits of this tree.     

Microsatellite analysis of genetic population structure in an endangered salmonid: the coastal cutthroat trout (Oncorhynchus clarki clarki)

The genetic population structure of coastal cutthroat trout ( Oncorhynchus clarki clarki ) in Washington state was investigated by analysis of variation in allele frequencies at six highly polymorphic microsatellite loci for 13 anadromous populations, along with one outgroup population from the Yellowstone subspecies ( O. clarki bouvieri) (mean heterozygosity = 67%; average number of alleles per locus = 24). Tests for genetic differentiation revealed highly significant differences in genotypic frequencies for pairwise comparisons between all populations within geographical regions and overall population subdivision was substantial ( F _ST = 0.121, R _ST = 0.093), with 44.6% and 55.4% of the among-population diversity being attributable to differences between streams ( F _SR = 0.054) and between regions ( F _RT = 0.067), respectively. Analysis of genetic distances and geographical distances did not support a simple model of isolation by distance for these populations. With one exception, neighbour-joining dendrograms from the Cavalli-Sforza and Edwards' chord distances and maximum likelihood algorithms clustered populations by physiogeographic region, although overall bootstrap support was relatively low (53%). Our results suggest that coastal cutthroat trout populations are ultimately structured genetically at the level of individual streams. It appears that the dynamic balance between gene flow and genetic drift in the subspecies favours a high degree of genetic differentiation and population subdivision with the simultaneous maintenance of high heterozygosity levels within local populations. Results are discussed in terms of coastal cutthroat trout ecology along with implications for the designation of evolutionarily significant units pursuant to the US Endangered Species Act of 1973 and analogous conservation units.     

Low Inbreeding and High Pollen Dispersal Distances in Populations of Two Amazonian Forest Tree Species

Recent studies suggest that tropical tree species exhibit low inbreeding and high gene dispersal levels despite the typically low density of conspecifics in tropical forests. To examine this, we undertook a study of pollen gene dispersal and mating system of two Amazonian tree species. We analyzed 341 seeds from 33 trees at four microsatellite loci in a Carapa guianensis population from Brazil, and 212 seeds from 22 trees at four microsatellite loci in a Sextonia rubra population from French Guiana. Differentiation of allele frequencies among the pollen pool of individual trees was Φ_FT= 0.053 (95% CI: 0.027–0.074) for C. guianensis and Φ_FT= 0.064 (95% CI: 0.017–0.088) for S. rubra. The mean pollen dispersal distances were estimated at 69–355 m for C. guianensis , and 86–303 m for S. rubra , depending on the pollen dispersal model and the estimate of reproductive tree density used. The multi-locus outcrossing rate was estimated at 0.918 and 0.945, and the correlation of paternity at 0.089 and 0.096, for C. guianensis and S. rubra , respectively, while no significant levels of biparental inbreeding were detected. Comparing trees with high and low local density of conspecifics, we found no evidence for differences in inbreeding levels. The results are discussed within the framework of the emerging picture of the reproductive biology of tropical forest trees.     

CALCULATING LIMITS TO THE ALLOWABLE HUMAN-CAUSED MORTALITY OF CETACEANS AND PINNIPEDS

A simulation method was developed for identifying populations with levels of human-caused mortality that could lead to depletion, taking into account the uncertainty of available information. A mortality limit (termed the Potential Biological Removal, PBR , under the U. S. Marine Mammal Protection Act) was calculated as the product of a minimum population estimate ( N _MIN), one-half of the maximum net productivity rate ( R _MAX), and a recovery factor ( F _R). Mortality limits were evaluated based on whether at least 95% of the simulated populations met two criteria: (1) that populations starting at the maximum net productivity level ( MNPL ) stayed there or above after 20 yr, and (2) that populations starting at 30% of carrying-capacity ( K ) recovered to at least MNPL after 100 yr. Simulations of populations that experienced mortality equal to the PBR indicated that using approximately the 20th percentile (the lower 60% log-normal confidence limit) of the abundance estimate for N _MIN met the criteria for both cetaceans (assuming R _MAX= 0.04) and pinnipeds (assuming R _MAX= 0.12). Additional simulations that included plausible levels of bias in the available information indicated that using a value of 0.5 for F _R would meet both criteria during these "bias trials." It is concluded that any marine mammal population with an estimate of human-caused mortality that is greater than its PBR has a level of mortality that could lead to the depletion of the population. The simulation methods were also used to show how mortality limits could be calculated to meet conservation goals other than the U. S. goal of maintaining populations above MNPL .     

侧穗凤仙花的传粉生态和繁育系统

通过对峨眉山特有种侧穗凤仙花的开花生物学特性、花器官结构、传粉者种类和访花行为、繁育系统、花粉胚珠比(P/O)及花粉活力的研究.发现居群之间花的寿命变化比较大,它们的雄蕊期长,雌/雄蕊期比为0.12～0.17;花粉胚珠比达到4.6万,花粉在开花第一天有很高的活力(＞90%);传粉者为熊蜂和天蛾,熊蜂包括贞洁熊蜂、白背熊...     

Isozyme variation under different modes of reproduction in two clonal winter annuals, Sedum rosulato-bulbosum and Sedum bulbiferum (Crassulaceae)

We studied isozyme variation in two annual species that produce bulbils, Sedum rosulato-bulbosum , which includes both sexually reproducing plants and obligate clonal plants that result from triploidy (fertile and sterile S. rosulato-bulbosum , respectively), and an obligate clonal plant, Sedum bulbiferum , to examine the relationship between reproductive mode and isozyme variation. The sterile S. rosulato-bulbosum population exhibited no genotypic variation, but showed high genetic variation (gene diversity, H _e  = 0.60) because five of the six loci that we analyzed were heterozygous. Almost all ramets of S. bulbiferum across 20 populations shared an identical isozyme phenotype, although we could not identify the genetic basis of the phenotype. In contrast, fertile S. rosulato-bulbosum exhibited genotypic variation across the species, but comprised genotypically uniform and polymorphic populations whose genotypic variations correlated positively with the genetic variations within the populations ( H _e at the genet level per population ranged from 0.08 to 0.37). Genetic drift and habitat conditions inhibiting seedling recruitment may have caused this among-population variation. The results for sterile and fertile S. rosulato-bulbosum suggest that exclusive clonal reproduction causes low genotypic variation, but maintains genetic variation within individuals. Factors that affect the maintenance of genetic variation in these plants are discussed on the basis of these findings.     

High ratio of illegitimate visitation by small bees severely weakens the potential function of heteranthery

Aims In heterantherous plants, 'division of labor' among structurally different stamens, i.e. pollinating and feeding functions, has been thought to reduce the evolutionary conflict of relying on pollen both as the carrier of male gametes and as the food for pollinators. The key to successful division of labor among different sets of stamens is the size match between stamens and legitimate pollinators, which results in the precise deposition of pollen onto specific locations on pollinator's body and facilitates cross pollination. However, the potential impact of small illegitimate insects that are ubiquitous during the pollination process on the plant reproduction in heterantherous species has been largely neglected in previous studies and never been demonstrated experimentally.Methods Here, we investigated the functions of three different types of stamens in Commelina communis. The pollinator visitation, pollen removal and deposition were compared among flowers with different types of anthers emasculated at two natural populations. Moreover, the mating systems of C. communis in wild populations were estimated using microsatellite markers.Important findings Our data showed that the main floral visitors for C. communis at the two studied populations were small illegitimate bees rather than legitimate pollinators, accounting for 77.5 and 92.2% of total flower visits, respectively. Flower manipulations in C. communis demonstrated that the two types of brightly yellow stamens separately functioned as 'deceptive attraction' and 'feeding' functions. Although the brown inconspicuous stamens of C. communis with the largest amount of fertile pollen had the potential function in offering pollen for cross pollination, the high ratio of illegitimate visitation by small bees significantly affected the dispersal and deposition of pollen from the pollinating anthers, and subsequently decreased the levels of outcrossing (t m = 0.23–0.32) in wild populations. Our work further confirmed that the size match between pollinators and the floral morphology is the prerequisite to successfully fulfill the functional differentiation among different sets of stamens in heterantherous plants. Local high ratio of illegitimate visitation by size unmatched insects could significantly weaken the potential functions of heteranthery, affecting the dispersal and deposition of functional pollen in heterantherous plants and further the whole mating systems.     

Genetic and in vitro molecular hybridization of malate dehydrogenase isozymes in interspecific bass (Micropterus) hybrids

Supernatant malate dehydrogenase (MDH) isozymes (as visualized by starch gel electrophoresis) are encoded by two distinct gene loci in both the largemouth and smallmouth bass. When an interspecific F₁ hybrid is formed between these two fish, a unique MDH isozyme is generated. The results of freeze-thaw molecular hybridization (which is the first application of this technique to MDH) indicate that this unique isozyme in the F₁ hybrid is a heterodimer composed of one subunit of each parental type. The F₁ hybrids produced F₂ hybrids which in turn formed the F₃ hybrid population. The inheritance of alleles at the MDH-B locus is consistent with a single Mendelian autosomal locus. Furthermore, there is no evidence of linkage between the lactate dehydrogenase-E locus and the MDH-B locus.