Morphometric measurements and carcass characteristics of Black Australorp, Naked Neck, and Rhode Island Red crossbreds under alternative production systems / Medições morfométricas e características de carcaça de Black Australorp, Naked Neck e Rhode Island Red crossbreds sob sistemas de produção alternativos

The present trial explained the effect of alternative production systems on growth, morphometric and carcass traits of four different chicken genotypes. The second generation of two genotypes RNN (Rhode Island Red × Naked Neck) and BNN (Black Australorp × Naked Neck) obtained by two self-crosses (RNN × RNN = RR and BNN × BNN = BB) and two reciprocal crosses (RNN × BNN = RB and BNN × RNN = BR) were evaluated in three alternative production systems (conventional cages, enriched cages, and aviary). At the 6th week of age after sexing, a total of 600 birds, comprising 150 from each crossbred with a total of 300 pullets and 300 cockerels were divided into conventional cages, enriched cages, and aviary systems having 200 birds in each.Birds were organized into 3×4 factorial arrangements under Completely Randomized Design (3 production systems × 4 genotypes × 2 sexes × 25 birds = 600 birds). Regarding genotypes, RB and BR males showed higher (p < 0.01) carcass yield, drumstick weight, breast weight, and thigh weight than BB and RR genotypes. Females of BR genotype showed higher (p < 0.01) breast weight, thigh weight and drumstick weight. As far as production systems are concerned, higher (p < 0.01) liver weight, heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight were observed in the males reared in enriched cages compared with conventional cages and aviary system. Females reared in enriched cages showed higher (p < 0.01) heart weight, breast weight, intestinal weight, drumstick weight, and thigh weight when compared with those reared in conventional cages and aviary. It is concluded that chickens (both sexes) of BR and RB genotypes had better morphological measurements and carcass traits than those of RR and BB genotype chickens. Among alternative production systems, chickens reared in enriched cages had better traits than those of reared in conventional cages and aviary during the growing phase.

O presente estudo explicou o efeito de sistemas alternativos de produção sobre o crescimento, características morfométricas e carcaças de quatro genótipos de frango diferentes. A segunda geração de dois genótipos RNN (Rhode Island Red × Naked Neck) e BNN (Black Australorp × Naked Neck) obtida por duas autocruzes (RNN × RNN = RR e B ANN × BNN = BB) e duas cruzes recíprocas (RNN × BNN = RB e BNN × RNN = BR) foi avaliada em três sistemas de produção alternativos (gaiolas convencionais, gaiolas enriquecidas e aviário). Na 6ª semana de idade após o sexo, um total de 600 aves, compostas por 150 de cada raça cruzada com um total de 300 pullets e 300 galos, foi dividido em gaiolas convencionais, gaiolas enriquecidas e sistemas aviários com 200 aves em cada. As aves foram organizadas em 3×4 arranjos fatoriais sob projeto completamente randomizado (3 sistemas de produção × 4 genótipos × 2 sexos × 25 aves = 600 aves). Em relação aos genótipos, os machos RB e BR apresentaram maior rendimento de carcaça (p < 0,01), peso da baqueta, peso mamário e peso da coxa do que os genótipos BB e RR. As fêmeas do genótipo BR apresentaram maior (p < 0,01) peso mamário, peso da coxa e peso da baqueta. No que diz respeito aos sistemas de produção, maior (p < 0,01) peso hepático, peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa foram observados nos machos criados em gaiolas enriquecidas em comparação com gaiolas convencionais e sistema aviário. As fêmeas criadas em gaiolas enriquecidas apresentaram maior (p < 0,01) peso cardíaco, peso mamário, peso intestinal, peso da baqueta e peso da coxa quando comparadas com as criadas em gaiolas convencionais e aviárias. Conclui-se que as galinhas (ambos os sexos) dos genótipos BR e RB apresentaram melhores medidas morfológicas e traços de carcaça do que os de frangos genótipos RR e BB. Entre os sistemas de produção alternativos, [...].

Genome-wide development of polymorphic microsatellite markers and their application in peanut breeding program

BACKGROUND: Cultivated peanut (Arachis hypogaea. L) represents one of the most important oil crops in the world. Although much effort has been expended to characterize microsatellites or Simple Sequence Repeats (SSRs) in peanut, the quantity and quality of the markers in breeding applications remain limited. Here, genome-wide SSR characterization and marker development were performed using the recently assembled genome of the cultivar Tifrunner. RESULTS: In total, 512,900 microsatellites were identified from 2556.9-Mb genomic sequences. Based on the flanking sequences of the identified microsatellites, 7757 primer pairs (markers) were designed, and further evaluated in the assembled genomic sequences of the tetraploid Arachis cultivars, Tifrunner and Shitouqi, and the diploid ancestral species, A. duranensis and A. ipaensis. In silico PCR analysis showed that the SSR markers had high amplification efficiency and polymorphism in four Arachis genotypes. Notably, nearly 60% of these markers were single-locus SSRs in tetraploid Arachis species, indicating they are more specific in distinguishing the alleles of the A and B sub-genomes of peanut. In addition, two markers closely related with purple testa color and 27 markers near to FAD2 genes were identified, which could be used for breeding varieties with purple testa and high-oleic acid content, respectively. Moreover, the potential application of these SSR markers in tracking introgressions from Arachis wild relatives was discussed. CONCLUSIONS: This study reported the development of genomic SSRs from assembled genomic sequences of the tetraploid Arachis Tifrunner, which will be useful for diversity analysis, genetic mapping and functional genomics studies in peanut

Production of wheat-doubled haploids resistant to eyespot supported by marker-assisted selection

BACKGROUND: Wheat is one of the most important crops cultivated all over the world. New high-yielding cultivars that are more resistant to fungal diseases have been permanently developed. The present study aimed at the possibility of accelerating the process of breeding new cultivars, resistant to eyespot, by using doubled haploids (DH) system supported by marker-assisted selection. RESULTS: Two highly resistant breeding lines (KBP 0916 and KBH 4942/05) carrying Pch1 gene were crossed with the elite wheat genotypes. Hybrid plants of early generations were analyzed using endopeptidase EpD1 and two SSR markers linked to the Pch1 locus. Selected homozygous and heterozygous genotypes for the Pch1-linked EpD1b allele were used to produce haploid plants. Molecular analyses were performed on haploids to identify plants possessing Pch1 gene. Chromosome doubling was performed only on haploid plants with Pch1 gene. Finally, 65 DH lines carrying eyespot resistance gene Pch1 and 30 lines without this gene were chosen for the eyespot resistance phenotyping in a field experiment. CONCLUSIONS: Results of the experiment confirmed higher resistance to eyespot of the genotypes with Pch1 in comparison to those without this gene. This indicates the efficiency of selection at the haploid level.

Use of a domestic Korean black goat (Capra hircus coreanae) with its chest crayon-harnessed in detecting estrus of Himalayan tahrs (Hemitragus jemlahicus)

The reliability of a Korean black goat (Capra hircus coreanae) to detect estrus in Himalayan tahrs (Hemitragus jemlahicus) for an artificial breeding program was investigated. Estrus in six female Himalayan tahrs was synchronized using fluorogestone acetate (FGA) sponges. Thirteen days later, 200 IU of PMSG and 100 IU of hCG were injected before removing the sponges and simultaneously injecting 5 mg of PGF2alpha the next day. Penetration of the cervical canal and the thickness and location of red crayon marks were examined 40~43 h later. Two females treated with sponges containing 60 or 45 mg of FGA had estrogen levels of 8.7 and 11.1 pg/mL, respectively. No red marks were found on the backs of these two tahrs. The remaining females had higher levels of estradiol, and the red crayon marks were clearly shown. The cervical folds of these tahrs were readily penetrated and the insemination gun was smoothly inserted into the uterine body. In conclusion, a Korean domestic goat with its chest crayon-harnessed was successfully used to detect estrus of Himalayan tahrs. This technique might be utilized as a part of breeding programs for wild goats and avoid the need for a vasectomy of conspecific males.

Qualidade da carne de bovinos superprecoces terminados em confinamento / Quality of meat from super-young cattle finished in feedlot

Avaliou-se a qualidade da carne de 10 bovinos F1 Guzerá-Nelore e 10 F2 Pardo Suíço-Guzerá-Nelore, inteiros, e abatidos precocemente. Na avaliação da carne, foi utilizado o músculo Longissimus dorsi. O delineamento experimental foi o inteiramente ao acaso. Verificaram-se para F1 e F2, respectivamente, médias para umidade de 75,3 e 75,1, extrato etéreo de 1,4 e 1,5, proteína de 23,7 e 23,6 e cinzas de 1,04 e 1,06. Cor em L* de 28,9 e 30,3, médias para cor em a* de 22,6 e 23,4 e cor em b* de 15,3 15,4, força de cisalhamento de 3,4 e 3,5, perda de peso pelo descongelamento de 9,8 e 10,5 e perda pelo cozimento de 15,9 e 15,6. Não houve diferença estatística para nenhuma das variáveis analisadas entre os grupos genéticos.

The purpose of this study was to use instrumental analysis to evaluate the chemical composition and fatty acid profile of 10 cattle Guzerath-Nellore (F1) and 10 Brown Swiss-Guzerath-Nellore (F2), intact and feedlot finished and slaughtered at 13 months. The Longissimus dorsi was used for meat evaluation. The experimental design was completely randomized. Humidity for F1 and F2 was respectively 75,3 and 75,1 averages, 1,4 and 1,5 averages for ether extract, proteins were 23,7 and 23,6 and 1,04 and 1,06 averages for ash. The results for F1 and F2, respectively, with averages for color to L * of 28,9 and 30,3, averages for the color to a* of 22,6 and 23,4 and color to b * 15,3 and 15,4, averages for shear force of 3,4 and 3,4, weight loss by thawing of 9,8 and 10,5 and weight lost by cooking of 15,9 and 15,4. There were no differences in genetic groups analysis.

Using genomics to improve fruit quality

New fruit varieties are needed to satisfy consumers, and the industry is facing new challenges in order to respond to these demands. The emergence of genomic tools is releasing information on polymorphisms that can be utilized to expedite breeding processes in species that are difficult to breed, given the long periods of time required to get new varieties. The present review describes the current stages of the ongoing efforts that are being taken to apply these technologies to obtain varieties with improved fruit quality in species of the family Rosaceae.

Science of breeding and heredity from ancient Persia to modern Iran.

About 1700 years BC, the prophet Zoroaster declared equal right for women and men to choose their “own ways.” There is much evidence that ancient Persians believed in the equal contribution of women and men toward producing a child, and all its hereditary characteristics. Even more surprising are the phrases in Vandidad book, which were gathered by Mobedans in the Mad dynasty about egg extraction (gametes) from animal reproductive organs (gonads) and their storage for future conception. Centuries later, Western philosopher beliefs in regard to reproduction were contrary to Persian knowledge. The Greek philosophers believed that man's water (semen) contains all human characteristics, and the female uterus is only responsible for nurturing and development of fetus. After detection of the ovum (de Graaf 2nd half 17 century) Malpigy proposed the preformation theory (ovist) which means there is a miniature human inside ovum, that grows after Semen has entered the uterus and grow into a well-developed fetus. This hypothesis was later delegated to spermatozoa. These contradictory and inappropriate beliefs were subject to discussions and dispute, until C.E. Wolf demonstrated that the embryo is a product of the fertilization of ovum by spermatozoa. 800 years prior this the sage Ferdowsi “The Great Iranian Poet” explains nicely the equal participation of man and woman in the production of the fetus and transmission of characters. After the renaissance and especially in recent years, tremendous achievements have been made in unraveling biological secrets of reproduction. There was no work o n genetics in Iran until 1936, when a genetic course was added to the biology curriculum in related colleges and universities; Iranian Genetics Society was founded in 1966, initiating a steady movement in this field. Although there was an inevitable gap during the revolution and war in our country, now there is great effort by researchers to eliminate the gap and bring us into the mainstream of world science, and development in biomedical sciences in the third millennium.

Obesity associated pathophysiological & histological changes in WNIN obese mutant rats.

Background & objectives: WNIN/Ob (obese and euglycaemic) and WNIN/GR-Ob (obesity with impaired glucose tolerance), were isolated and established from Wistar rat stock (WNIN). Both strains showed physical, physiological and biochemical indices related to obesity. We present here haematology, histology and pathophysiological changes between the phenotypes of these strains, lean (+/+), carrier (+/-) and obese (-/-). Methods: A total of 72 animals of equal gender consisting of three phenotypes were used for the study. Haematology, organ weights were measured and histopathology of the tissues studied using standard procedures. In 12 lean and obese rats (equal gender) of WNIN/GR-Ob group morphometry of pancreatic islets was done immunohistochemically (IHC). Results: Obese rats of both the strains showed normal haematology (except low platelet count), but exhibited changes in the organ weights and in histopathology in organs like liver, kidney, brain and testis/ovary. Hyperplasia of adipocytes was seen in obese rats as compared to lean and carrier. IHC of obese rat pancreas showed that both islet density and volume were significantly (P<0.05) increased compared to lean littermates. Interpretation & conclusions: The histological and pathophysiological changes seen in these mutants were in tune with obese phenotype exhibited by these animals.

WNIN/GR-Ob - An insulin-resistant obese rat model from inbred WNIN strain.

Background & objectives: WNIN/GR-Ob is a mutant obese rat strain with impaired glucose tolerance (IGT) developed at the National Institute of Nutrition (NIN), Hyderabad, India, from the existing 80 year old Wistar rat (WNIN) stock colony. The data presented here pertain to its obese nature along with IGT trait as evidenced by physical, physiological and biochemical parameters. The study also explains its existence, in three phenotypes: homozygous lean (+/+), heterozygous carrier (+/-) and homozygous obese (-/-). Methods: Thirty animals (15 males and 15 females) from each phenotype (+/+, +/-, -/-) and 24 lean and obese (6 males and 6 females) rats were taken for growth and food intake studies respectively. Twelve adult rats from each phenotype were taken for body composition measurement by total body electrical conductivity (TOBEC); 12 rats of both genders from each phenotype at different ages were taken for clinical chemistry parameters. Physiological indices of insulin resistance were calculated according to the homeostasis model assessment for insulin resistance (HOMA-IR) and also by studying U14C 2-deoxy glucose uptake (2DG). Results: WNINGR-Ob mutants had high growth, hyperphagia, polydipsia, polyurea, glycosuria, and significantly lower lean body mass, higher fat mass as compared with carrier and lean rats. These mutants, at 50 days of age displayed abnormal response to glucose load (IGT), hyperinsulinaemia, hypertriglyceridaemia, hypercholesterolaemia and hyperleptinaemia. Basal and insulin-stimulated glucose uptakes by diaphragm were significantly decreased in obese rats as compared with lean rats. Interpretation & conclusions: Obese rats of the designated WNIN/GR-Ob strain showed obesity with IGT, as adjudged by physical, physiological and biochemical indices. These indices varied among the three phenotypes, being lowest in lean, highest in obese and intermediate in carrier phenotypes thereby suggesting that obesity is inherited as autosomal incomplete dominant trait in this strain. This mutant obese rat model is easy to propagate, and can easily be transformed to frank diabetes model by dietary manipulation and thus can be used for screening anti-diabetic drugs.

Breeding habitats characterization of anopheles mosquito [diptera: culicidae] in Najran province, Saudi Arabia

An ecological study on mosquito larval breeding habitats was conducted in Najran Region, Saudi Arabia during 2005-2006 to study the breeding habitats determinants for Anopheles mosquito in two ecological types [cities and villages]. The increased rate of developmental activities promotes man-made mosquito breeding habitats, which regulate Anopheles mosquito abundance or absence. The linear regression analysis revealed that An. gambiae s.L abundance or absence is regulated by the presence of natural water habitats, which has the highest rate [79%] in villages. Other ecological, biological and physiochemical predictors for Anopheles mosquito larvae abundance or absence in the two ecological types were discussed

Mapping aluminum tolerance loci in cereals: a tool available for crop breeding

Aluminum (Al) toxicity is the main factor limiting crop productivity in acidic soils around the world. In cereals, this problem reduces crop yields by 30-40 percent. The use of DNA-based markers linked to phenotypic traits is an interesting alternative approach. Strategies such as molecular marker-assisted selection (MAS) in conjunction with bioinformatics-based tools such as graphical genotypes (GGT) have been important for confirming introgression of genes or genomic regions in cereals but also to reduce the time and cost of identifying them through genetic selection. These biotechnologies also make it possible to identify target genes or quantitative trait loci (QTL) that can be potentially used in similar crops to increase their productivity. This review presents the main advances in the genetic improvement of cereals for Al-tolerance.

Genetic diversity within and between broodstocks of the white shrimp Litopenaeus vannamei (Boone, 1931) (Decapoda, Penaeidae) and its implication for the gene pool conservation

Genetic variation within and between fifteen closed broodstock lines of the Pacific white shrimp Litopenaeus vannamei, reared at different hatcheries in the Brazilian coast, was assessed by RAPD analysis. Fifty two polymorphic loci were identified when a set of five decamer primers was used in PCR. The genetic diversity analysis within lines evidenced genetic variation loss probably related to bottleneck effects and inbreeding. In addition, the genetic divergence values between the different samples appear to reflect the initial founder composition of such stocks, in some cases, sharing a common origin, suggesting a putative importance of interbreeding for the establishment of genetic improvement programs for these broodstocks. The genetic variation monitoring appears to be helpful to the gene pool conservation of this aquaculture species, mainly if considered its exotic status in Brazil and the current impossibility of new introduction of wild individuals.

A variação genética existente dentro e entre quinze linhagens fechadas de reprodutores do camarão branco Litopenaeus vannamei, mantidas em diferentes laboratórios de larvicultura na costa brasileira, foi estudada utilizando análises RAPD. Através de um conjunto de cinco iniciadores decâmeros em PCR, foram identificados 52 locos polimórficos. A análise da diversidade genética dentro de cada linhagem evidenciou perda da variação genética provavelmente devida a efeitos de bottleneck e endocruzamento. Em adição, os valores de divergência genética entre as diferentes linhagens parecem refletir a composição inicial de fundação desses estoques, em alguns casos, compartilhando uma origem comum, sugerindo uma importância potencial do exo-cruzamento para estabelecer programas de melhoramento genético baseado nessas linhagens reprodutoras. O monitoramento da variação genética será muito útil para a conservação do conjunto gênico desta espécie de aquacultura, especialmente se for considerado seu status exótico no Brasil e que atualmente é impossível a realização de novas introduções de indivíduos selvagens.

A general review of competition genetic effects with an emphasis on swine breeding

A review of previous studies is presented on estimates of genetic parameters and responses to selection with traditional breeding approaches, on correlations between agonistic behavior and growth performance, and on theoretical frameworks for selection incorporating interactions among individuals and on practical methods for incorporating competition effects in breeding programs.

Pedigree analyses in the Breeding Program for Nellore Cattle

Parameters based on the probability of gene origin were used to describe genetic variability in three reproductive groups from the Breeding Program for Nellore Cattle (PMGRN). The three reproductive populations (cows in reproductive age, bulls from artificial insemination centers and young bulls in progeny test) generated medium to low values. The effective number of founders (Nf ), the effective number of ancestors (Na) and the remaining genomes (Ng) suggest low founder representativeness, high genetic contribution by some ancestors, considerable loss of founder alleles and lack of allelic representativeness in bulls kept in artificial insemination centers and young sires in progeny test in relation to the diversity on the farms participating in the PMGRN. The parameters based on the probability of gene origin in the three reproductive groups were: 84.3, 53 and 54.2 (Nf ); 71, 36.6 and 30 (Na) and 51.4, 19.3 and 19 (Ng) for cows, bulls from artificial insemination centers and young sires in progeny test, respectively. Future matings and the introduction of selected progeny reproduction may decrease the parameters based on the probability of gene origin in each reproductive group, thereby increasing considerably the additive relationship in the three reproductive groups and consequently increasing the probability of inbreeding in the future. Strategies to maintain genetic variability in bull populations must be implemented.

Biomphalaria tenagophila: dynamics of populations of resistant and susceptible strains to Schistosoma mansoni, with or without pressure of the parasite

Resistant (Taim, RS) and susceptible albino (Joinville, SC) Biomphalaria tenagophila populations were kept together, at different proportions, throughout a 18-month-period. Some of the snail groups were submitted to Schistosoma mansoni infection. The targets of this study were (a) to analyze the populational dynamics among resistant and susceptible individuals to S. mansoni; (b) to study the resistance phenotype in descendants of cross-breeding; (c) to observe whether the parasite could exert any kind of selection in those snail populations. Throughout the experiment it could be observed that the susceptible B. tenagophila strain (Joinville) underwent a selective pressure of the parasite that was negative, since the individuals showed a high mortality rate. Although B. tenagophila (Taim) population presented a higher mortality rate without pressure of the parasite, this event was compensated by a reproductive capacity. B. tenagophila Taim was more fecund than B. tenagophila Joinville and was able to transmit the resistance character to their descendants. F1 generation obtained by cross-breeding between resistant and susceptible lineages was completely resistant to S. mansoni infection, irrespective of the Taim proportion. Moreover, less than 5 percent of F2 progeny were susceptible to S. mansoni infection.

Laboratory colonization of Mansonia mosquitoes with an emphasis on Ma. annulata and Ma. bonneae.

The present study records the first successful colonization of Mansonia annulata and describes colony maintenance with modification of rearing medium and host plants. Three species of Mansonia mosquitoes (Ma. uniformis, Ma. indiana and Ma annulifera) were successfully reared in ambient environments with adult emergence rates > 50%, while Ma. bonneae and Ma. dives yielded emergence rates > 30%. Colonization of Ma. annulata was modified and improved so that they were successfully raised to adult with emergence rates of 23%. Tube sedge, Lepironia articulata, was utilized as a host plant and peat swamp water was used as a rearing medium. Yeast and small lizard droppings were added daily to the larval medium to maintain microorganisms and pH in the infusion. However, identifying suitable culture medium remains an obstacle to establishing colonies of Ma. annulata, as the culture medium is difficult to mimic in the laboratory. Further study, focusing particularly on larval attachment substrates and rearing medium, is needed to develop a standardized and practical rearing technique for Mansonia mosquitoes.

Maintenance and breeding of Thrichomys (Trouessart, 1880) (Rodentia: Echimyidae) in captivity

South American histricognath rodents Thrichomys apereoides laurentius and Thrichomys pachyurus are natural hosts of Trypanosoma cruzi, agent of Chagas disease. We established breeding colonies of these species to serve as experimental models in various parasitological studies. Both species of Thrichomys have all the requirements necessary to become excellent laboratory models: they can be easily maintained in the standard laboratory conditions and breed throughout the year and they do not have any special dietary demands and can be fed by standard food pellets designed for laboratory mice. Both species produce precocious offspring that have their eyes and ears open, teeth erupted, fur well developed, and can eat solid food in the first week of life. T. a. laurentius has larger litter sizes and lower body masses at birth and weaning than T. pachyurus. Moreover, females of T. a. laurentius reach puberty earlier and with lower body mass than T. pachyurus.

Evaluation of crosses of Holstein, Jersey or Brown Swiss sires x Holstein-Friesian/Gir dams. 3. Lifetime performance and economic evaluation

Lifetime dairy production, reproduction and growth traits of 75 females sired by Holstein, Jersey or Brown Swiss bulls and Holstein-Friesian x Gir dams of 1/2 to 3/4 Holstein-Friesian fractions were compared. The animals were in a single herd under the same management. Milk, fat and protein yields, concentrates fed, reproduction, and weights were recorded throughout the lifetime of the cows. The data were analyzed by least squares techniques under models including the fixed effects of breed of sire, Bos taurus fraction and year of birth. Herd lifes for Holstein, Jersey and Brown Swiss crosses were 6.006 +/- 0.812, 8.129 +/- 0.863 and 7.247 +/- 0.777 years. Milk yields per day of herd life were 7.150 +/- 0.266, 6.757 +/- 0.282 and 6.249 +/- 0.254 kg. Weights of cull cows sold were 458 +/- 15, 415 +/- 15 and 457 +/- 13 kg. Based on these and on previously reported results of the same experiment, intakes of roughage and pasture were estimated from energy requirements. Lifetime expenditures on concentrates, roughages, pastures, milking, reproduction, and heifer rearing were calculated based on mean performance of each breed of sire, as well as on receipts from animals and milk sold (the latter with four sets of prices of protein, fat and carrier). The conclusion was that in systems of artificial female calf rearing and male calf wastage, the Jersey crosses appear to offer important economic benefits to farmers, which would be even greater if payment on milk protein and fat becomes effective

Biomphalaria tenagophila: dominant character of the resistance to Schistosoma mansoni in descendants of crossbreedings between resistant (Taim, RS) and susceptible (Joinville, SC) strains

The aim of the present work was to study parasitological, molecular, and genetic aspects in descendants of crossbreedings between a totally resistant Biomphalaria tenagophila strain (Taim, RS) and another one highly susceptible (Joinville, SC) to Schistosoma mansoni. Descendants F1 and F2 were submitted to S. mansoni infection (LE strain). The susceptibility rates for individuals from Group F1 were 0 to 0.6 percent, and from Group F2 was 7.2 percent. The susceptible individuals from Group F2 discharged a lower number of cercariae, when compared with the susceptible parental group, and in 2 out of 9 positive snails the cercarial elimination was discontinued. In order to identify genetic markers associated with resistance the genotype of parental snails and their offspring F1 and F2 were analyzed by means of the randomly amplified polymorphic DNA method. Nevertheless, it was not possible to detect any marker associated to resistance, but the results showed that in the mentioned species the resistance character is determined by two dominant genes.