Showing papers in "Genetics and Molecular Biology in 1998"

Programa GENES: Aplicativo Computacional em Estatística Aplicada à Genética (GENES - Software for Experimental Statistics in Genetics)

Abstract: The main purpose of the GENES software is to help people working with genetic analysis and data processing in breeding programs, using several biometrics models. This software has several help windows that are very friendly to the user. More information about this program is available in the book" Programa GENES - Aplicativo Computacional em Genetica e Estatistica, 442. 1997". Purchase orders are welcome at the following address: editora@mail.ufv.br. Shareware copies of the GENES software are available at http://www.genetica.dbg.ufv.br.

Genetic variation in body weight gain and composition in the intercross of Large (LG/J) and Small (SM/J) inbred strains of mice

Abstract: Strain intercross experiments provide a powerful means for mapping genes affecting complex quantitative traits. We report on the genetic variability of the intercross of the Large (LG/J) and Small (SM/J) inbred mouse strains as a guide to gene mapping studies. Ten SM/J males were crossed to 10 LG/J females, after which animals were randomly mated to produce F1, F2, and F3 intercross generations. The 1632 F3 animals from 200 full-sib families were used to estimate heritabilities and genetic correlations of the traits measured. A subset of families was cross-fostered at birth to allow measurement of the importance of post-natal maternal effects. Data was collected on weekly body weight from one to 10 weeks and on organ weights, body weight, reproductive fat pad weight, and tail length at necropsy in the intercross generations. There was no heterosis for age-specific weights or necropsy traits, except that one-week weight was the highest in the F2 generation, indicating heterosis for maternal effect in the F1 mothers. We found moderate to high heritability for most age-specific weights and necropsy traits. Maternal effects were significant for age-specific weights from one to four weeks but disappeared completely at ten-week weight. Maternal effects for necropsy traits were low and not statistically significant. Age-specific weights showed a typical correlation pattern, with correlation declining as the difference in ages increased. Among necropsy traits, reproductive fat pad and body weights were very highly genetically correlated. Most other genetic correlations were low to moderate. The intercross between SM/J and LG/J inbred mouse strains provides a valuable resource for mapping quantitative trait loci for body size, composition, and morphology

Genetic diversity characterization of cassava cultivars (Manihot esculenta Crantz).: I) RAPD markers

Abstract: RAPD markers were used to investigate the genetic diversity of 31 Brazilian cassava clones. The results were compared with the genetic diversity revealed by botanical descriptors. Both sets of variates revealed identical relationships among the cultivars. Multivariate analysis of genetic similarities placed genotypes destinated for consumption "in nature" in one group, and cultivars useful for flour production in another. Brazil’s abundance of landraces presents a broad dispersion and is consequently an important resource of genetic variability. The botanical descriptors were not able to differentiate thirteen pairs of cultivars compared two-by-two, while only one was not differentiated by RAPD markers. These results showed the power of RAPD markers over botanical descriptors in studying genetic diversity, identifying duplicates, as well as validating, or improving a core collection. The latter is particularly important in this vegetatively propagated crop.

Comparative cytogenetic and morphological analysis of Astyanax scabripinnis paranae (Pisces, Characidae, Tetragonopterinae)

Abstract: Cytogenetic and morphological studies were carried out on nine local populations of Astyanax scabripinnis paranae. All populations exhibited 2n = 50 chromosomes as well as conspicuous differences involving karyotype morphology, number and position of nucleolar organizer regions (NORs) and amount and/or locations of constitutive heterochromatin blocks. A quantitative study of the cytogenetic data showed that eight populations possessed different karyotypes. Morphological analyses based on nine measurements and two meristic parameters were effective in establishing clear identification of five populations. Comparative analysis of cytogenetic and morphological traits suggests that chromosomal changes have occurred at a more rapid rate than morphological differentiation. Despite the close morphological similarity found among some populations, chromosomal differentiation was identified in all of them, even in those presenting only small morphological differences.

Cytogenetic and morphometric differences in populations of Astyanax "scabripinnis" (Pisces, Characidae) from Maringá region, PR, Brazil

Abstract: A cytogenetic and morphometric study of four populations of characid fish assigned to the "complex" of Astyanax scabripinnis originating from three riverine basins, namely Ivai (populations A and B), Paranapanema (C) and Parana (D), was carried out. Karyological analysis showed the diploid chromosome number 2n = 48 for population B and 2n = 50 for the remaining populations. All populations under study differed in the composition of karyotypes and C-banding patterns. Canonical variable analysis used to assess the morphometric data revealed that 1) the four populations under study were entirely discriminated from each other and 2) the coefficients that most contributed to this pattern were standard length, rostrodorsal distance, eye diameter and snout length. The results indicate that the differences in karyotypes were paralleled by the morphological differentiation of the populations under study and contributed to the problem of systematics of A. scabripinnis "complex".

Identification of zygotic and nucellar tangerine seedlings (Citrus spp.) using RAPD

Abstract: The randomly amplified polymorphic DNA (RAPD) technique was used to distinguish nucellar and zygotic seedlings resulting from crosses between the ‘Montenegrina’ (Citrus deliciosa Tenore) and‘ King’ (C. nobilis Loureiro) tangerines. The aim of the present study was to develop tangerine varieties with a reduced number of seeds and organoleptic characteristics similar to the ‘Montenegrina’ tangerine. Embryos were isolated from seeds, cultivated in vitro, and acclimated in a greenhouse. Four random primers were used to identify 54 plants of sexual origin from a total of 202 individuals. The degree of polymorphism of each primer was reflected in the number of zygotic plants obtained per primer. Cluster analysis of parents and progeny separated the individuals into distinct groups with a maximum genetic dissimilarity of 20%.

Molecular biogeography of the Neotropical fish Hoplias malabaricus (Erythrinidae:Characiformes) in the Iguaçu, Tibagi, and Paraná Rivers

Abstract: Hoplias malabaricus, the common trahira, extended its range into the Iguacu River sometime in the last decades. To determine levels of genetic differentiation in neighboring basins of this nominal taxon, as well as to unveil the source of the invading population, we analyzed patterns of similarity of RAPD-PCR genomic markers of samples from Parana, Iguacu and Tibagi Rivers. The high genetic diversity of samples from the Parana and Tibagi Rivers suggested strong population structuring or even the occurrence of undescribed species. All alleles of the sample from the headwaters of Tibagi River were present in the sample from the Iguacu River, which suggests that the former population or another population with similar genetic makeup, may be the source of the trahiras of the Iguacu River.

Origin of the hemoglobin S gene in a northern Brazilian population: the combined effects of slave trade and internal migrations

Abstract: Com o objetivo de investigar a origem da mutacao bS na populacao da regiao norte do Brasil, foram analisados polimorfismos de DNA no complexo de genes b da hemoglobina em 30 pacientes com anemia falciforme na populacao de Belem, a capital do Estado do Para. Sessenta e sete por cento dos cromossomos bS analisados apresentaram o haplotipo Bantu, 30% o haplotipo Benin e 3% o haplotipo Senegal. A origem da mutacao bS na populacao de Belem, estimada de acordo com a distribuicao de haplotipos, nao esta de acordo com a esperada com base em dados historicos sobre o trafico de escravos para a regiao norte, os quais indicam uma reduzida contribuicao de escravos da regiao do Benin. Essas diferencas podem ser atribuidas ao trafico interno de escravos, bem como ao posterior fluxo de populacoes imigrantes, particularmente de nordestinos. A distribuicao de haplotipos em Belem nao difere significativamente da observada em outras regioes brasileiras, muito embora os dados historicos sugiram que a maioria dos escravos procedentes da regiao do Atlântico-Oeste africano, onde predomina o haplotipo Senegal, foi trazida para o norte do Brasil, enquanto que o nordeste (Bahia, Pernambuco e Maranhao) recebeu o maior contingente de escravos oriundos da regiao centro-oeste africana, onde o haplotipo Benin e o mais comum. Nos sugerimos que as diferencas regionais quanto a procedencia dos escravos africanos tambem foram modificadas pelo trafico de escravos estabelecido entre as diferentes regioes brasileiras e posteriormente pelos movimentos migratorios.

Karyotypes and heterochromatin variation (C-bands) in Melipona species (Hymenoptera, Apidae, Meliponinae)

Abstract: We describe the karyotypes of eight bee species of the genus Melipona and compare them in terms of heterochromatin content and location (C-banding technique). All species had 2n = 18 (females) and n = 9 (males) chromosomes, but a wide variation in heterochromatin content was detected among karyotypes. On the basis of these differences, the species were divided into two functional groups, one of them comprising species with a karyotype having a low heterochromatin content (M. bicolor bicolor, M. quadrifasciata, M. marginata, and M. asilvai), and the other species with a high heterochromatin content (M. seminigra fuscopilosa, M. capixaba, M. scutellaris, and M. captiosa). In the species with high heterochromatin content, heterochromatin occupied practically the entire extent of all chromosomes, with euchromatin being limited to the extremities, a fact that prevented observation of the centromere. In contrast, in the species with karyotypes having a low heterochromatin content, heterochromatin was visualized only in some chromosomes. In the chromosomes in which it was present, heterochromatin was located in the centromere or on the short arm. M. bicolor bicolor had the smallest heterochromatin content with only three chromosome pairs presenting heterochromatin in females. Increased heterochromatin content may be explained by interstitial and pericentromeric growth.

Leuciscus (Pisces, Cyprinidae) karyotypes: Transect of Portuguese populations

Abstract: The presently described Iberian chubs - Leuciscus carolitertii and L. pyrenaicus - sampled throughout their distribution ranges in Portugal were cytogenetically analyzed. Their chromosome numbers were consistently 2n = 50, except for two specimens of L. carolitertii, which exhibited a supernumerary chromosome in some of the metaphases. The karyotypes were found to be highly typical for other Leuciscus taxa, as well as for European leuciscine cyprinids: the chromosome sets are dominated by metacentric and submetacentric elements with a reduced number of acrocentric pairs (three to four); the largest pair of the complements belongs typically to this latter category. The chubs from northern drainages, assignable to L. carolitertii, have apparently a more stable karyotype structure (12M:30S:8A) than the chubs from L. pyrenaicus, which have 12M:32S:6A, but may exhibit in the most southern river basins (Guadiana, Mira, Aljezur, Bordeira and Arade) more variable karyotypes. Besides, these data support the very recent discovery of two genetically distinct Leuciscus taxa in this region of the Iberian Peninsula, suggesting the stochastic fixation of structural chromosome rearrangements in these small and isolated drainages, which may be affected by bottlenecks due to significant variations in hydrological regimes. The NORs were apparently located in one small submetacentric pair of chromosomes and the presence of a heteromorphic sex chromosome system of the ZW/ZZ type was also evidenced for the Iberian endemic chubs.

Mutagenic activity of airborne particulate matter from the urban area of Porto Alegre, Brazil

Abstract: The mutagenic activity of airborne particulate matter collected from three different sites within the urban area of Porto Alegre, Brazil, was investigated using a Salmonella/microsome assay. Samples were extracted by sonication, sequentially, with cyclohexane (CX), and dichloromethane (DCM), for a rough fractionation by polarity. The different fractions were tested for mutagenicity using Salmonella typhimurium strains TA98, with and without metabolic activation (S9 mix fraction), and TA98NR and TA98/1,8-DNP6, without metabolic activation. Mutagenic response was observed for frameshift strain TA98 in assays with and without metabolization for two sites (sites 2 and 3), which had considerable risk of environmental contamination by nonpolar (CX) and/or moderately polar (DCM) compounds. However, the values of revertants/m3 (rev/m3) were highest on the site subject to automobile exhaust (site 3) in assays without (9.56 rev/m3) and with metabolization (5.08 rev/m3). Maximum mutagenic activity was detected in the moderately polar fraction, decreasing after metabolization. Nevertheless, the nonpolar fractions (CX) gave higher mutagenic activity in the presence of metabolization than in the absence of the S9 mix fraction. The responses observed for TA98NR and TA98/1,8-DNP6 strains suggest the activity of nitrocompounds.

Early selection for growth vigor in rubber tree genotypes in northwestern São Paulo State (Brazil)

Abstract: Forty-five genotypes (clones) of rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. Arg.] of different origins were assessed for efficiency of early selection at the Votuporanga Experimental Station in northwestern Sao Paulo State, Brazil, using a randomized complete block design with three replications and six plants per plot. Girth at 120 cm above the highest point of the grafting union of each tree was taken at ages 12, 24, 36, 48, 60, 72, 84 and 96 months. Highly significant differences in girth were detected among the genotypes at all ages evaluated, except for 12 months. Estimates of genetic variance for two age sets showed a substantial increase with age, while the genotype variation decreased. Selection made at 24 months proved to be the most efficient, giving a superior gain per unit of time.

Nuclear DNA content of thirty species of Neotropical fishes

Abstract: The present paper reports nuclear DNA content in 30 Neotropical freshwater fish species and summarizes the data on other Neotropical species presented in the literature. Among Neotropical fishes, the nuclear DNA content ranges from 1.04 ± 0.09 pg/nucleus in Corydoras cf. simulatus (2n = 62) to 248.0 pg/nucleus in Lepidosiren paradoxa (2n = 38). A general analysis of the data obtained in the present study for each species showed that DNA measurements were practically constant at the individual level, while significant differences were observed among individuals of the same population. This observation was valid for all species analyzed and was more evident in those species that presented other karyotypic particularities such as sex chromosomes or supernumerary chromosomes. The importance of changes in nuclear DNA content in the evolutionary process of Neotropical fishes is discussed.

Karyotype similarity between two sympatric schizodon fish species (anostomidae, characiformes) from the paraguay river basin

Abstract: Fish of the neotropical family Anostomidae generally show low karyotype variability. Nevertheless, karyotype variants have been identified within some genera, providing information about their evolutionary history. Species of the genus Schizodon show a high degree of morphological and ecological similarity compared to other anostomids. In the present study, karyotype characteristics of Schizodon borelli (40 individuals) and S. isognathum (one individual), two sympatric species found in the Paraguay River basin, were studied. C-banding, GC-specific fluorochrome Mitramycin (MM) and Ag staining as well as in situ hybridization (FISH) with rDNA probes were used. The karyotypes of these species were found to be very similar. Only two NORs were detected in a common chromosome pair of both species under Ag, MM and FISH treatments. Similar heterochromatin distribution patterns were also observed. A parallelism between the small karyotype variation and low morphological and ecological divergence observed for this genus is discussed. Their karyotype homogeneity might be related to populational features or, alternatively, might indicate that the maintenance of a symmetric and conserved karyotype structure represents optimal genomic organization among these fish.

Interspecific hybridization and inbreeding effect in seed from a Eucalyptus grandis x E. urophylla clonal orchard in Brazil

Abstract: We used allozyme markers to estimate the amount of natural hybridization between Eucalyptus grandis and E. urophylla in a 7.4-hectare commercial hybrid-seed orchard planted in Espirito Santo, Brazil. This orchard was planted in 1982 using a honeycomb design, with each hexagonal plot containing one E. grandis tree surrounded by six E. urophylla trees. There were 267 replicated hexagonal plots in the orchard. Seeds were harvested from the E. grandis clone only. The multilocus outcrossing rate estimated for the E. grandis clone averaged 70.2%, ranging from 33.0 to 99.0% among individual trees. Contaminant pollination, inferred from progeny genotypes containing alleles not present in the seven parental clones, accounted for 14.4% of the hybrid seed. Contaminant pollen was attributed to neighboring eucalyptus stands isolated from the orchard by a 400-m wide belt of native forest. Inbred and hybrid progenies were identified by their allozyme genotypes and transplanted to the field. Field growth of inbred progeny was 30% lower than that of hybrid plants at two and three years of age.

Evidence of apomixis in cassava (Manihot esculenta Crantz)

Abstract: Apomixis maintains heterosis and avoids transmission of systemic pathogens which accompany vegetative propagation of cassava. An embryonic study of cleared ovules of two cassava clones in toto showed them to be of aposporic nature. Cytogenetic analysis of the two clones revealed an aneuploid structure (2n + 1) in apomictic individuals, whereas it was 2n in the sexually reproduced plants.

Screening cotton genotypes for seedling drought tolerance

Abstract: The objectives of this study were to adapt a screening method previously used to assess seedling drought tolerance in cereals for use in cotton (Gossypium hirsutum L.) and to identify tolerant accessions among a wide range of genotypes. Ninety genotypes were screened in seven growth chamber experiments. Fifteen-day-old seedlings were subjected to four 4-day drought cycles, and plant survival was evaluated after each cycle. Three cycles are probably the minimum required in cotton work. Significant differences (at the 0.05 level or lower) among entries were obtained in four of the seven experiments. A "confirmation test" with entries previously evaluated as "tolerant" (high survival) and "susceptible" (low survival) was run. A number of entries duplicated their earlier performance, but others did not, which indicates the need to reevaluate selections. Germplasms considered tolerant included: `IAC-13-1', `IAC-RM4-SM5', `Minas Sertaneja', `Acala 1517E-1' and `4521'. In general, the technique is simple, though time-consuming, with practical value for screening a large number of genotypes. Results from the screening tests generally agreed with field information. The screening procedure is suitable to select tolerant accessions from among a large number of entries in germplasm collections as a preliminary step in breeding for drought tolerance. This research also demonstrated the need to characterize the internal lack of uniformity in growth chambers to allow for adequate designs of experiments.

A new karyotype for the genus Cavia from a southern island of Brazil (Rodentia - Caviidae)

Abstract: RESUMO A variacao cariotipica nas especies de mamiferos e bastante comum e geralmente causada pela fusao de cromossomos acrocentricos. Foi descrito neste trabalho um novo cariotipo, com 2n = 62 e FN = 112, para o genero Cavia proveniente das ilhas Moleques do Sul, da costa sul do Brasil. Foram analisados os cariotipos de dois machos e quatro femeas que possuiam 24 pares de cromossomos com dois bracos e seis pares de acrocentricos. O par sexual era constituido por um cromossomo X metacentrico grande e um Y acrocentrico. As bandas C estavam localizadas nas regioes centromericas e pericentromericas da maioria dos cromossomos, com excecao de alguns acrocentricos e os cromossomos de dois bracos menores. As regioes organizadoras de nucleolo ocorreram em dois cromossomos com dois bracos e o padrao de bandamento G foi tambem apresentado.

Effect of gamma-radiation and sodium azide on quantitative characters in rice (Oryza sativa L.)

Abstract: Seeds of rice cultivar IAC-1246 received single and combined treatments of 10 or 20 Krad gamma-rays and 0.5 mM sodium azide (SA). The experiments were carried out to assess the effect of treatments on the mean and variance in second generation plants of the following quantitative traits: number of days to flowering (NDF), culm length (CL) and tiller number (TN). In general, the mutagenic treatments increased variance, but did not change the mean for the characters NDF and CL in the M2 generation. There was no increase in the mean or variance of TN. The combined treatments of gamma-rays and SA resulted in larger variance in CL than for the treatments with gamma-rays alone, but not higher than obtained with SA alone. Combined treatments with gamma-rays and SA did not increase the variance of NDF and TN when compared with the corresponding single treatments.

A new method to estimate genetic gain in annual crops

Abstract: The genetic gain obtained by breeding programs to improve quantitative traits may be estimated by using data from regional trials. A new statistical method for this estimate is proposed and includes four steps: a) joint analysis of regional trial data using a generalized linear model to obtain adjusted genotype means and covariance matrix of these means for the whole studied period; b) calculation of the arithmetic mean of the adjusted genotype means, exclusively for the group of genotypes evaluated each year; c) direct year comparison of the arithmetic means calculated, and d) estimation of mean genetic gain by regression. Using the generalized least squares method, a weighted estimate of mean genetic gain during the period is calculated. This method permits a better cancellation of genotype x year and genotype x trial/year interactions, thus resulting in more precise estimates. This method can be applied to unbalanced data, allowing the estimation of genetic gain in series of multilocational trials.

Chromosomal variation, macroevolution and possible parapatric speciation in Mepraia spinolai (Porter) (Hemiptera: Reduviidae)

Abstract: Mepraia spinolai is an endemic species in Chile that lives in wild and domestic habitats. It is the only species of the Reduviidae family that shows alate polymorphism; females are always wingless, but males can be found with and without wings. The M. spinolai karyotype consists of 10 pairs of autosomes and a complex sex determination system. Males from the northernmost regions I and II (latitude 18°-26° South) are always winged (braquipterous) and are X1X2Y, with a large Y chromosome. From region III to the metropolitan region (latitude 26°-33° South), males may be either winged or wingless but appear to be polymorphic for a small neo-Y chromosome, which may have originated by fracture of the large holocentric Y chromosome found in populations from farther north. Experimental crosses suggest that the genes for wings are linked in the Y chromosome and also that there are two cytologically indistinguishable types of neo-Y chromosomes. One form (Y1) bears a gene or genes for wings while the other (Y2) lacks such genes. Males that are X1X2Y1, X1X2Y1Y1 and X1X2Y1Y2 are winged, while the absence of Y1 (X1X2Y2 and X1X2Y2Y2 ) results in a wingless male. These chromosomes and morphological changes are correlated with a shift of the southern population into more arid habitats of the interior in the metropolitan region and region III.

Genetics of the Pantaneiro horse of the Pantanal region of Brazil

Abstract: Genetic variation at seven red blood cell alloantigen, blood group loci and 10 biochemical genetic loci was examined in 102 Pantaneiro horses from the Pantanal region of Brazil and compared to that of other domestic horse breeds. Measures of both individual genic variation and populational genetic diversity within the Pantaneiro were near the average for domestic horse breeds. From the standpoint of genetic conservation there is no immediate concern for loss of variation within the Pantaneiro. Analysis of genetic relationship showed that the Pantaneiro was clearly of Iberian Peninsula descent and that it was most closely related to other Brazilian breeds.

Chromosome studies of some Vernonia species (Asteraceae)

Abstract: Chromosomes of 12 Vernonia species (Asteraceae) from South America were studied. First counts were reported for: V. alpestris Gardn. (n = 17), V. chalybaea Mart. ex DC. (2n = 32), V. cotoneaster Less. (2n = 30), V. fruticulosa Mart. ex DC. (n = 16) and V. lithospermifolia Hieron. (n = 10, 2n = 20). Furthermore, in V. aurea Mart. ex DC. (2n = 32), V. mollissima D. Don (n = 32) and V. saltensis Hieron. (2n = 64) numbers different from those reported in the literature were found. Karyotypes were described for some species. V. aurea contains 24m + 8sm chromosomes, V. chalybaea contains 22m + 10sm chromosomes, V. cincta Griseb. 36m + 16sm + 8st and V. cotoneaster 18m + 12sm. The basic chromosome numbers x = 10, 14, 15, 16 and 17 were confirmed for South American Vernonia species. The results are discussed in relation to previous chromosome studies for the genus.

Estimates of genetic parameters related to chitinase production by the entomopathogenic fungus Metarhizium anisopliae

Abstract: Chitinolytic activity and dry mass production were determined in culture filtrates from 17 Metarhizium anisopliae strains grown in liquid medium containing chitin as the only carbon source The objectives were to estimate parameters such as genetic variance among strains, heritability and expected gain from selection, as well as correlations between tested traits Wide genotypic variability was observed among strains in chitinolytic activity, permitting the exploitation of this property in selection The high heritability suggests that progress can be made through phenotypic selection The genotypic correlation coefficient between dry mass production and chitinolytic activity detected in the filtrates was negative (= - 0588) One of the isolates was also investigated for variation in the two traits as a function of culture growth time The results showed an increase in enzyme activity up to the 8th (and last) day of the experiment and a decrease in dry mass from the 4th day on

Use of lymphocyte cultures for BrdU replication banding patterns in anuran species (Amphibia)

Abstract: We describe the standardization of lymphocyte culture procedures in order to improve cytological preparations of anuran species. This methodology permits the use of 5-bromodeoxyuridine (BrdU) treatment to obtain replication banding patterns in the chromosomes of these species.

The karyotype of Alouatta fusca clamitans from Rio de Janeiro, Brazil: Evidence for a y-autosome translocation

Abstract: Os cariotipos referentes a quatro machos de Alouatta fusca clamitans oriundos do Rio de Janeiro foram analisados atraves de tecnicas de bandamento G, C e NOR. O numero diploide em todos os especimes foi igual a 49, com a presenca de tres cromossomos nao pareados. A comparacao dos padroes de bandamento G com especimes previamente descritos com 2n = 50 revelou a ocorrencia de uma translocacao do tipo Y-autossomo, modificando o sistema cromossomico de determinacao sexual para o tipo multiplo, X1X2Y/X1X1 X2X2. Os blocos de heterocromatina constitutiva se distribuiram na regiao pericentromerica de todos os cromossomos; segmentos intercalares e telomericos foram visualizados em um par acrocentrico e em outro submetacentrico, respectivamente. As regioes organizadoras de nucleolo se localizaram no braco longo de dois pares de pequenos acrocentricos.

Hierarchical structure of genetic distances: Effects of matrix size, spatial distribution and correlation structure among gene frequencies

Abstract: Geographic structure of genetic distances among local populations within species, based on allozyme data, has usually been evaluated by estimating genetic distances clustered with hierarchical algorithms, such as the unweighted pair-group method by arithmetic averages (UPGMA). The distortion produced in the clustering process is estimated by the cophenetic correlation coefficient. This hierarchical approach, however, can fail to produce an accurate representation of genetic distances among populations in a low dimensional space, especially when continuous (clinal) or reticulate patterns of variation exist. In the present study, we analyzed 50 genetic distance matrices from the literature, for animal taxa ranging from Platyhelminthes to Mammalia, in order to determine in which situations the UPGMA is useful to understand patterns of genetic variation among populations. The cophenetic correlation coefficients, derived from UPGMA based on three types of genetic distance coefficients, were correlated with other parameters of each matrix, including number of populations, loci, alleles, maximum geographic distance among populations, relative magnitude of the first eigenvalue of covariance matrix among alleles and logarithm of body size. Most cophenetic correlations were higher than 0.80, and the highest values appeared for Nei's and Rogers' genetic distances. The relationship between cophenetic correlation coefficients and the other parameters analyzed was defined by an "envelope space", forming triangles in which higher values of cophenetic correlations are found for higher values in the parameters, though low values do not necessarily correspond to high cophenetic correlations. We concluded that UPGMA is useful to describe genetic distances based on large distance matrices (both in terms of elevated number of populations or alleles), when dimensionality of the system is low (matrices with large first eigenvalues) or when local populations are separated by large geographical distances.

Beta-globin gene cluster haplotypes in the Mapuche Indians of Argentina

Abstract: Haplotypes derived from five polymorphic restriction sites in the beta-globin gene cluster were investigated in 86 chromosomes from the Argentinian Mapuche. These results were integrated with those previously obtained for ten Brazilian Indian tribes. Eight haplotypes were identified, the most frequent being 2 (57%) and 6 (27%). The presence of haplotype 3 in 2% of the Mapuche chromosomes is probably an evidence of admixture with individuals of African ancestry. Due to the high number of haplotypes observed, heterozygosity as measured by the Gini-Simpson index was higher in the Mapuche than in Brazilian Indians. The haplotypic distribution in the Mapuche was also significantly different from those of all Brazilian tribes investigated. This heterogeneity could be at least partially explained by admixture with non-Indian populations.

Growth trends, genotype-environment interaction and genetic gains in six-year-old rubber tree clones (Hevea) in São Paulo State, Brazil

Abstract: Budwood from seven different clones of rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. Arg.] was planted in replicated trials in four different test sites in the plateau region of the state of Sao Paulo, Brazil. The clones represented a range of imported germplasm, whereas the locations were selected to represent a range of rubber growing areas. Girths were measured for six years consecutively, before the initiation of tapping for latex. Total number of latex vessel rings (lvr) and bark thickness (bt) were measured at six years. The largest average for all characters was observed in Matao. Overall means for girth, total number of latex vessel rings and bark thickness at six years were 35.26 cm, 11.30 units and 4.83 mm, respectively. Both the test sites and clones showed statistically significant differences in girth, lvr and bt values. There were significant clone x site interactions. Girth at one year was not a reliable predictor of future field performance. Broad sense heritability for girth was 0.16, and for lvr and bt it was 0.28 and 0.40, respectively, at six years. Repeatability was quite high, from 0.52 to 0.75 for all characters in all years. When two clones out of seven were selected, expected genetic gain in girth was about 2.0%; for lvr and bt it was 7.0% and 14.6%, respectively.

Birth weight of twins: 1. The fetal growth patterns of twins and singletons

Abstract: Distributions of birth weights of twins and singletons born at three southeastern Brazilian hospitals were compared after adjustment for gestational age, its quadratic and cubic terms, sex, type of pregnancy, as well as their interactions. The pattern of twin fetal growth rate was retarded in comparison to that of singletons, regardless of the socioeconomic level of the examined population, but the gestational age at which this retardation started seems to be correlated to the income of the mothers. In all cases, after 28 weeks of gestation, female fetal growth was slightly but consistently lower than that of males.