Classes Of Loci Research Articles

Identification of donor lines for improving fruit yield of k 35 x k 12 eggplant hybrid

The aim of this study was to identify an eggplant donor line which possess the largest frequency of favourable alleles that control fruit yield. Such donor line should be used to improve the elite eggplant hybride K35 x K12. The fruit yield of the elite hybrid, its parents and their hybrids with three potential donor lines (K36/1, K11 and K22/2) was examined in a diallel set by means of field trials. The trials were set in a randomized block design in three replications. After the fruit yield had been measured, the modified method of evaluation of relative loci value according to Dudley (1987) was applied. Ali inbred lines expressed positive values of the ?G' parameter. The K11 inbred had the largest ?G' value (2.38) and, also, the lowest frequency of unfavourable alleles on the loci class D (1.33). It was established that the K11 inbred line was more related to the K35 parental inbred line (7.81). Consequently, on the basis of the ?D' values, improvement should be obtained by backcrossing the elite hybrid K35 x K11 to the donor inbred K11.

Quantitative Trait Locus Analysis of Leaf Dissection in Tomato Using Lycopersicon pennellii Segmental Introgression Lines

Leaves are one of the most conspicuous and important organs of all seed plants. A fundamental source of morphological diversity in leaves is the degree to which the leaf is dissected by lobes and leaflets. We used publicly available segmental introgression lines to describe the quantitative trait loci (QTL) controlling the difference in leaf dissection seen between two tomato species, Lycopersicon esculentum and L. pennellii. We define eight morphological characteristics that comprise the mature tomato leaf and describe loci that affect each of these characters. We found 30 QTL that contribute one or more of these characters. Of these 30 QTL, 22 primarily affect leaf dissection and 8 primarily affect leaf size. On the basis of which characters are affected, four classes of loci emerge that affect leaf dissection. The majority of the QTL produce phenotypes intermediate to the two parent lines, while 5 QTL result in transgression with drastically increased dissection relative to both parent lines.

Characteristic numbers of rational curves with cusp or prescribed triple contact

This note pursues the techniques of [Graber-Kock-Pandharipande] to give concise solutions to the characteristic number problem of rational curves in $\boldsymbol P^2$ or $\boldsymbol P^1\times\boldsymbol P^1$ with a cusp or a prescribed triple contact. The classes of such loci are computed in terms of modified psi classes, diagonal classes, and certain codimension-2 boundary classes. Via topological recursions the generating functions for the numbers can then be expressed in terms of the usual characteristic number potentials.

Classes of degeneracy loci for quivers: The Thom polynomial point of view

The Chern classes for degeneracy loci of quivers are natural generalizations of the Thom-Porteous-Giambelli formula. Suppose that $E,F$ are vector bundles over a manifold $M$ and that $s : E\to F$ is a vector bundle homomorphism. The question is, which cohomology class is defined by the set $\Sigma\sb k(s)\subset M$ consisting of points $m$ where the linear map $s(m)$ has corank $k$? The answer, due to I. Porteous, is a determinant in terms of Chern classes of the bundles $E,F$. We can generalize the question by giving more bundles over $M$ and bundle maps among them. The situation can be conveniently coded by an oriented graph, called a quiver, assigning vertices for bundles and arrows for maps. We give a new method for calculating Chern class formulae for degeneracy loci of quivers. We show that for representation-finite quivers this is a special case of the problem of calculating Thom polynomials for group actions. This allows us to apply a method for calculating Thom polynomials developed by the authors. The method–reducing the calculations to solving a system of linear equations–is quite different from the method of A. Buch and W. Fulton developed for calculating Chern class formulae for degeneracy loci of $A\sb n$-quivers, and it is more general (can be applied to $A\sb n$-, $D\sb n$-, $E\sb 6$-, $E\sb 7$-, and $E\sb 8$-quivers). We provide sample calculations for $A\sb 3$- and $D\sb 4$-quivers.

A role for the Saccharomyces cerevisiae RENT complex protein Net1 in HMR silencing.

Silencing in the yeast Saccharomyces cerevisiae is known in three classes of loci: in the silent mating-type loci HML and HMR, in subtelomeric regions, and in the highly repetitive rDNA locus, which resides in the nucleolus. rDNA silencing differs markedly from the other two classes of silencing in that it requires a DNA-associated protein complex termed RENT. The Net1 protein, a central component of RENT, is required for nucleolar integrity and the control of exit from mitosis. Another RENT component is the NAD(+)-dependent histone deacetylase Sir2, which is the only silencing factor known to be shared among the three classes of silencing. Here, we investigated the role of Net1 in HMR silencing. The mutation net1-1, as well as NET1 expression from a 2micro-plasmid, restored repression at silencing-defective HMR loci. Both effects were strictly dependent on the Sir proteins. We found overexpressed Net1 protein to be directly associated with the HMR-E silencer, suggesting that Net1 could interact with silencer binding proteins and recruit other silencing factors to the silencer. In agreement with this, Net1 provided ORC-dependent, Sir1-independent silencing when artificially tethered to the silencer. In contrast, our data suggested that net1-1 acted indirectly in HMR silencing by releasing Sir2 from the nucleolus, thus shifting the internal competition for Sir2 from the silenced loci toward HMR.

Population structure of the tsetse fly Glossina pallidipes estimated by allozyme, microsatellite and mitochondrial gene diversities.

Diversities at nuclear and mitochondrial loci were examined in eleven natural populations of Glossina pallidipes from east and southern Africa. Alleles in each class of loci are assumed to be selectively neutral. Allozyme gene diversities (heterozygosities) averaged over eight loci were 0.146 among seven Kenya populations and 0.201 among four southern African populations. Microsatellite diversity averaged over three loci was 0.250 in Kenya and only 0.218 in southern Africa. Mitochondrial diversities averaged 0.504 in Kenya and only 0.156 in southern Africa. Mitochondrial and microsatellite diversities in the populations were strongly correlated with each other, but uncorrelated with allozyme diversities. In contrast to the allozyme diversities, mitochondrial and microsatellite variation indicated a severe and prolonged reduction in population size in southern Africa. Genetic distances among populations increased with the geographical distances between them. Allozyme diversities in southern populations were conserved. Genetic differentiation at allozyme loci among populations was greatly damped when compared with the other markers. The foregoing can be explained if allozyme diversities were maintained by balancing selection. Three main points emerged: genetic data confirm the historical evidence that southern G. pallidipes populations experienced a severe and prolonged bottleneck; allozyme variation was conserved in the bottlenecked populations; and gene flow among populations is surprisingly restricted.

Sexual selection, reproductive isolation and the genic view of speciation

Sexual selection, reproductive isolation and the genic view of speciation

The methylcitric acid pathway in Ralstonia eutropha: new genes identified involved in propionate metabolism.

From Ralstonia eutropha HF39 null-allele mutants were created by Tn5 mutagenesis and by homologous recombination which were impaired in growth on propionic acid and levulinic acid. From the molecular, physiological and enzymic analysis of these mutants it was concluded that in this bacterium propionic acid is metabolized via the methylcitric acid pathway. The genes encoding enzymes of this pathway are organized in a cluster in the order prpR, prpB, prpC, acnM, ORF5 and prpD, with prpR transcribed divergently from the other genes. (i) prpC encodes a 2-methylcitric acid synthase (42720 Da) as shown by the measurement of the respective enzyme activity, complementation of a prpC mutant of Salmonella enterica serovar Typhimurium and high sequence similarity. (ii) For the translational product of acnM the function of a 2-methyl-cis-aconitic acid hydratase (94726 Da) is proposed. This protein and also the ORF5 translational product are essential for growth on propionic acid, as revealed by the propionic-acid-negative phenotype of Tn5-insertion mutants, and are required for the conversion of 2-methylcitric acid into 2-methylisocitric acid as shown by the accumulation of the latter, which could be purified as its calcium salt from the supernatants of these mutants. In contrast, inactivation of prpD did not block the ability of the cell to use propionic acid as carbon and energy source, as shown by the propionic acid phenotype of a null-allele mutant. It is therefore unlikely that prpD from R. eutropha encodes a 2-methyl-cis-aconitic acid dehydratase as proposed recently for the homologous prpD gene from S. enterica. (iii) The translational product of prpB encodes 2-methylisocitric acid lyase (32314 Da) as revealed by measurement of the respective enzyme activity and by demonstrating accumulation of methylisocitric acid in the supernatant of a prpB null-allele mutant. (iv) The expression of prpC and probably also of the other enzymes is regulated and is induced during cultivation on propionic acid or levulinic acid. The putative translational product of prpR (70895 Da) exhibited high similarities to PrpR of Escherichia coli and S. enterica, and might represent a transcriptional activator of the sigma-54 family involved in the regulation of the other prp genes. Since the prp locus of R. eutropha was very different from those of E. coli and S. enterica, an extensive comparison of prp loci available from databases and literature was done, revealing two different classes of prp loci.

Length of uninterrupted repeats determines instability at the unstable mouse expanded simple tandem repeat family MMS10 derived from independent SINE B1 elements.

Mouse expanded simple tandem repeats (ESTRs) provide highly informative loci for analyzing spontaneous and induced germline mutation. We have conducted an extensive sequence database search and identified 17 new members of the highly unstable rodent-specific ESTR family called MMS10. This family has arisen by independent expansions of a common GGCAGA repeat unit from within a subset of both ancestral and modern SINE B1 elements during the course of mouse evolution. Analysis of the interspersion patterns of variant repeats along alleles of 20 of these MMS10 loci revealed two distinct classes of tandem arrays: one composed of uninterrupted GGCAGA repeats and the second with generally larger arrays interrupted by variant units. Surveys of allelic diversity at 11 representative members of these two classes of loci in various laboratory strains and BXD recombinant inbred lines revealed that the level of repeat instability was positively correlated with the length of uninterrupted repeats. Turnover processes at MMS10 loci, therefore, appear similar to the type of mechanism observed at human microsatellites. The MMS10 family thus provides a potentially useful murine model for studying dynamic mutation at simple tandem repeats.

Calibrating bacterial evolution

Estimations of the rate of mutation in bacteria have been based on the assumption that the rates of accumulation of DNA sequence divergence are similar in prokaryotes and in higher eukaryotes. Unfortunately, the factors that determine the rate of molecular evolution, such as population size, generation time and mutation rate per generation, differ in bacteria and higher eukaryotes. Furthermore, the data estimated for bacterial species for which molecular evolution can be dated from ecological or geological evidence have sometimes been used as a reference, yet comparisons of the relative rates of mutagenesis at different classes of genomic loci indicate that they cannot be universally applied to all bacteria. However, there is evidence based on laboratory observations that microorganisms have a constant mutation rate per genome per generation. It has been demonstrated that, although the genome sizes and average mutation rates per base pair vary by 3–4 orders of magnitude, the mutation rate per genome is remarkably stable. Ochman et al.1 Ochman H. et al. Calibrating bacterial evolution. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 12638-12643 Crossref PubMed Scopus (327) Google Scholar compared the mutation rates estimated by sequence comparisons with those determined from laboratory experiments. They found that the genomic mutation rate for Escherichia coli and Buchnera does indeed seem to be constant across an evolutionary time scale. The estimated mutation rate is 0.0001–0.0002 per genome per replication, which is 30 times lower than the rate based on laboratory studies. If this pattern is true for other bacterial taxa, it will be valuable for calibrating bacterial evolution.

Active macromolecule uptake by lymph node antigen-presenting cells: a novel mechanism in determining sentinel lymph node status.

Although sentinel lymph node (SLN) biopsy is a powerful staging tool for patients with melanoma and breast cancer, controversy remains regarding specific aspects of technique. We examined particle uptake by antigen-presenting cells (APCs) to determine if this mechanism is responsible for the differential retention of radioactivity in SLNs relative to nonsentinel lymph nodes (NSLNs). Mapping was conducted in pigs injected with vital blue dye, fluoroscein isothiocyanate-labeled human serum albumin (FITC-HSA), and one of two 99mtechnetium-labeled tracers, i.e., human serum albumin, a small macromolecule, or unfiltered sulfur colloid, a mixture of small and large particles. Macromolecule uptake by APCs was studied in vitro by using FITC-HSA and measured by fluorescence-activated cell sorting (FACS). SLNs and NSLNs were analyzed by fluorescence microscopy or FACS, with counterstaining for leukocyte cell surface markers. Both radiotracers were effective. Cultured APCs rapidly took up FITC-HSA. Microscopy showed FITC-HSA in the subcapsular sinus of SLNs shortly after injection and subsequent distribution to interfollicular areas. FACS revealed increasing amounts of FITC-HSA in SLNs over time. Cells responsible for uptake were APCs, expressing major histocompatibility (locus) class II. This report establishes active macromolecule uptake as a mechanism that determines SLN status. This mechanism has important implications for performing SLN biopsy.

Oxidative stress and aging in Caenorhabditis elegans.

Aging is controlled by a complex interplay of both genetic and environmental factors. Because of this, many theories have been advanced that seek to explain the etiology of both cellular and organismal aging (Jazwinski 1996; Holliday 1997). In some cases, these theories are not mutually exclusive. One particularly popular theory posits that free radicals, especially those of molecular oxygen, can accelerate aging (Harman 1986). Martin et al. (1996) have eloquently articulated seven different classes of genetic loci that could modulate aging through oxidative damage. These include, for example, genes that would affect the generation of free radicals and others that modulate the scavenging of free radicals. A third class is those genes that specify repair enzymes. In addition, Cutler (1985) summarized a variety of data that support the notion that oxidative damage impacts aging. These include correlations between either free radical production or defenses against free radicals as compared with aging or life span. For example, the product of the standard metabolic rate and the maximum life span is roughly constant for various animals, indicating that animals with lower standard metabolic rates can live for longer periods than animals with higher rates. This concept, called the LEP (life-span energy potential), strongly suggests that oxygen radicals may exacerbate aging. More directly, the concentration of antioxidants in various mammalian tissues is inversely related to their maximum life-span potential (MLSP).

Human Cytomegalovirus US3 Gene Expression Is Regulated by a Complex Network of Positive and Negative Regulators

One immediate early gene of human cytomegalovirus, the US3 gene, causes retention of major histocompatibility locus class I heavy chain proteins in the endoplasmic reticulum and is postulated to have a role in viral pathogenicity. Expression of the US3 gene is regulated by a number of cis-acting elements. In addition, numerous viral proteins are involved in regulating US3 gene expression. US3 transcription was activated modestly by a virion protein, ppUL82. The immediate early proteins encoded by UL122–123 (IE1 and IE2) further activate US3 expression, with the activation enhanced by expression of pTRS1. Other proteins, the immediate early protein encoded by UL37ex1/UL38 and the early protein, pUL84, inhibited IE1 and IE2 activation of US3 expression. US3 transcription is regulated both positively and negatively by a complex network of viral proteins, the interaction of which contributes to precise regulation of US3 gene expression. The ability of pUL37ex1/UL38 to repress expression of the immediate early US3 gene while activating early gene expression suggests that pUL37ex1/UL38 may function to switch viral gene expression from immediate early to early genes.

A study of loss of heterozygosity at 70 loci in anaplastic astrocytoma and glioblastoma multiforme with implications for tumor evolution.

Cancers that arise from astrocytes in the adult CNS present as either anaplastic astrocytomas (AAs) or as more aggressive glioblastomas multiforme (GBMs). GBMs either form de novo or progress from AAs. We proposed to examine the molecular genetic relationship between these CNS tumors by conducting a genome-wide allelic imbalance analysis that included 70 loci on examples of AA and GBM. We found significant loss of heterozygosity (LOH) at 13 discrete chromosomal loci in both AAs and GBMs. Loss was significant in both AAs and GBMs at 9 of these loci. AAs show the highest rates of LOH at chromosomes 1p, 4q, 6p, 9p, 11p, 11q, 13q, 14q, 15p, 17p, 17q, and 19q. GBMs showed the greatest losses at 1p, 6q, 8p, 9p, 10p, 10q, 11p, 13q, 17p, 17q, 18p, 18q, and 19q. GBMs also demonstrated significant amplification at the epidermal growth factor receptor locus (7p12). These data suggest that there are three classes of loci involved in glioma evolution. First are loci that are likely involved in early events in the evolution of both AAs and GBMs. The second class consists of AA-specific loci, typified by higher LOH frequency than observed in GBMs (4q, 6p, 17p, 17q, 19q). The third class consists of GBM-specific loci (6q, 8p, 10, 18q). Damage at these loci may either lead to de novo GBMs or permit existing AAs to progress to GBMs. Glioma-related LOH profiles may have prognostic implications that could lead to better diagnosis and treatment of brain cancer patients.

HLA class I allele distributions in six Pacific/Asian populations: evidence of selection at the HLA-A locus.

The distributions of HLA-A alleles in six Pacific/Asian populations, Malay, Papua New Guinea (PNG) Highlands, two Indonesian groups, and two PNG Lowland groups, as well as the distribution of the HLA-B alleles in the PNG Highlands population, were determined using polymerase chain reaction (PCR) immobilized sequence-specific oligonucleotide (SSO) probe typing methods. The allele frequency distributions at the HLA class II loci, DRB1, DQB1 and DPB1 were also determined by PCR/SSO methods in an additional study of the same populations. In most of these populations, the HLA-A*2402 allele was the most frequent, attaining a frequency of 0.78 in the PNG Highlands. A*1101 was the next most frequent allele, followed in frequency by the *3401 allele. The HLA-B*1506, *4001, *5601 and *5602 alleles comprised 73% of the allele diversity at the B-locus in the PNG Highlands. Two previously unreported HLA-A alleles were identified in Indonesians and Malays, based on novel probe reactivity patterns. Cloning and sequencing identified these as A*1104 and *2410. Sequence comparisons show that these new alleles differ at codon 187 from their putative parental alleles (*1101 and *2403) by dinucleotide changes in the first two codon positions. These changes involve a Thr to Arg (CG to AC) and an Arg to Thr substitution (AC to CG) at position 187; residues at this position participate in pocket A of the peptide binding groove. Comparison of the HLA-A allele frequency distributions indicate that Malays are the most diverse (heterozygosity (h)=0.88) and the PNG Highlanders are, by far, the least diverse (h=0.37) of the groups studied. However, the diversity of B-locus alleles in the PNG Highlanders (h=0.91) was greater than that observed at the A-locus of any of the populations reported here. The remarkably high allele frequency of A*2402 in the PNG Highlands could reflect founder effects and population bottlenecks, genetic drift, or positive directional selection. The distribution of the HLA-B locus alleles and class II alleles, as well as mtDNA sequence data in the PNG Highlands indicates a reasonably high level of diversity at other loci, arguing that the high frequency of A*2402 cannot be attributed entirely to founder effects, bottlenecks, or drift and suggests the operation of positive selection for the A*2402 allele in this population.

Genomic organization around the centromeric end of the HLA class I region: large-scale sequence analysis.

We previously sequenced two regions around the centromeric end of HLA class I and the boundary between class I and class III. In this paper we analyze the two regions of about 385 kb and confirm, giving a new line of evidence, that the following two pairs of the genomic segments were duplicated in evolution: (i) a 43-kb genomic segment including the HLA-B gene showing the highest polymorphism among the classical HLA class I loci (class Ia) and a 40-kb segment including the HLA-C locus showing the lowest polymorphism and (ii) a 52-kb segment including the MIC (MHC class I chain related gene) B and a 35-kb segment including MICA. We also found that repetitive elements such as SINEs, LINEs, and LTRs occupy as much as 47% of nucleotides in this 385-kb region. This unusually high content of repetitive elements indicates that repeat-mediated rearrangements have frequently occurred in the evolutionary history of the HLA class Ia region. Analysis of LINE compositions within the two pairs of duplicated segments revealed that (i) LINEs in these regions had been dispersed prior to both the duplication of the HLA-B and -C loci and the duplication of the MICB and MICA loci, and (ii) the divergence of the HLA-B and -C loci occurred prior to the duplication of the MICA and MICB loci. To find novel genes responsible for HLA class I-associated or other diseases, we performed computer analysis applying GenScan and GRAIL to GenBank's dbEST. As a result, at least five as yet uncharacterized genes were newly mapped on the HLA class I centromeric region studied. These novel genes should be analyzed further to determine their relationships to diseases associated with this region.

The utility of short tandem repeat loci beyond human identification: implications for development of new DNA typing systems.

Since the first characterization of the population genetic properties of repeat polymorphisms, the number of short tandem repeat (STR) loci validated for forensic use has now grown to at least 13. Worldwide variations of allele frequencies at these loci have been studied, showing that variations of interpopulation diversity at these loci do not compromise the power of identification of individuals. However, data collected for validation of these loci for forensic use has utility beyond human identification; the origin and past migration history of modern humans can be reconstructed from worldwide variations at these loci. Furthermore, complex forensic cases previously unresolvable can now be investigated with the help of the validated STR loci. Here, we provide the absolute power of the validated set of 13 STR loci for addressing these issues using multilocus genotype data on 1,401 individuals belonging to seven populations (US European-American, US African-American, Jamaican, Italian, Swiss, Chinese and Apache Native-American). Genomic research is discovering new classes of polymorphic loci (such as the single nucleotide polymorphisms, SNPs) and lineage markers (such as the mitochondrial DNA and Y-chromosome markers); our aim, therefore, was to determine how many SNP loci are needed to match the power of this set of 13 STR loci. We conclude that the current set of STR loci is adequate for addressing most problems of human identification (including interpretations of DNA mixtures). However, if suitable number of SNPs are used that would match the power of the STR loci, they alone cannot resolve more complex cases unless they are supplemented by the validated STR loci.

Identifying open-pollinated populations of field corn as sources of cold tolerance for improving sweet corn

Sweet corn has poor cold tolerance and adaptation to the European Atlantic coast. Our objectives were to identify sources of favorable alleles for improving cold tolerance of three sweet corn hybrids, to compare sources of cold tolerance and early vigor, and to provide additional information on the relationships among different classes of loci and estimators of favorable alleles for cold tolerance. Each of ten field corn populations was crossed to four sweet corn inbreds. The field by sweet corn hybrids, the populations, the inbreds and the target hybrids were evaluated under cold conditions. Estimates of the mean frequencies of four classes of loci in the populations, and six estimators of favorable alleles (lplμ', PTC, UBND, NI, PNGg, and PNGceg) and GCA were computed. The population by inbred crosses were significantly different for emergence proportion and survival. Correlations between lplμ', UBND, PTC and NI were high for emergence proportion. Most estimates of favorable alleles were significantly different from zero but not among populations. PTC was used to choose the best potential donor populations. The US Corn Belt Dent population AS-3(HT)C3 and the Spanish flint population Oroso were the best potential donors of favorable alleles for emergence proportion and survival under cold conditions, respectively. The ability to germinate and survive under cold conditions may be necessary, but it does not ensure adaptation to cold humid springs.

Identification of Field Corn Inbreds Adapted to Europe to Improve Agronomic Performance of Sweet Corn Hybrids

Elite American and European field corn inbreds (Zea mays L.) could improve the agronomic value of sweet corn for European conditions. The choice of field corn inbreds for improvings weet corn performance can be accomplished by a variety of methods. Our objectives were to identify American and European field corn inbreds adapted to European conditions as potential donors for improving yield and agronomic performance of sweet corn hybrids, and to provide additional information on the relationships among different estimators of favorable alleles when the donor lines show better performance than the inbred lines to be improved. Eleven field corn inbreds were crossed to seven sweet corn inbreds that were parents of seven sweet corn hybrids. The field × sweet corn hybrids and inbreds were evaluated separately in field trials at two locations in northwesternS paini n 1993 and 1994. Yield and four agronomic traits were recorded. Estimates of the relative number of alleles at six classes of loci (B, C, D, E, F, and G) were computed, and the methods for identifying field corn inbreds with favorable alleles were an estimate of favorable dominant alleles present in the donor but not in the hybrid (μG’), predicted threeway cross (PTC), minimum upper bound (UBND), net improvement (NI), probability of net gain of favorable alleles given complete dominance (PNGg)and given partial dominance or complementarye pistasis (PNGceg), and general combining ability (GCA). Correlations between μG’, UBND, PTC, NI, and GCA were very high for all traits. The field corn inbreds A632, EP42, and EP29 were identified as the best potential donors for improving yield and several yield components of sweet corn hybrids. European flint inbreds offer new possibilities for improving the agronomic value of sweet corn and its adaptation to cold areas with short growing seasons.

Microsatellite diversity and the demographic history of modern humans.

We have examined differences in diversity at 60 microsatellite loci among human population samples from three major continental groups to evaluate the hypothesis of greater African diversity in this rapidly evolving class of loci. Application of a statistical test that assumes equal mutation rates at all loci fails to demonstrate differences in microsatellite diversity, while a randomization test that does not make this assumption finds that Africans have significantly greater microsatellite diversity (P < 10(-8)) than do Asians and Europeans. Greater African diversity is most apparent at loci with smaller overall variance in allele size, suggesting that the record of population history has been erased at repeat loci with higher mutation rates. A power analysis shows that only 35-40 microsatellites are needed to establish this difference statistically, demonstrating the considerable evolutionary information contained in these systems. On average, African populations have approximately 20% greater microsatellite diversity than do Asian and European populations. A comparison of continental diversity differences in microsatellites and mtDNA sequences suggests earlier demographic expansion of the ancestors of Africans.