RESUMO
Subterminal satellite (StSat) repeats, consisting of 32-bp-long AT-rich units (GATATTTCCATGTT(T/C)ATACAGATAGCGGTGTA), were first found in chimpanzee and gorilla (African great apes) as one of the major components of heterochromatic regions located proximal to telomeres of chromosomes. StSat repeats have not been found in orangutan (Asian great ape) or human. This patchy distribution among species suggested that the StSat repeats were present in the common ancestor of African great apes and subsequently lost in the lineage leading to human. An alternative explanation is that the StSat repeats in chimpanzee and gorilla have different origins and the repeats did not occur in human. The purpose of the present study was quantitative evaluation of the above alternative possibilities by analyzing the nucleotide variation contained in the repeats. We collected large numbers of sequences of repeat units from genome sequence databases of chimpanzee and gorilla, and also bonobo (an African great ape phylogenetically closer to chimpanzee). We then compared the base composition of the repeat units among the 3 species, and found statistically significant similarities in the base composition. These results support the view that the StSat repeats had already formed multiple arrays in the common ancestor of African great apes. It is thus suggested that humans lost StSat repeats which had once grown to multiple arrays.
Assuntos
DNA Satélite/genética , Evolução Molecular , Hominidae/genética , Sequências Repetitivas de Ácido Nucleico/genética , Animais , Sequência de Bases , Genoma Humano , Gorilla gorilla/genética , Heterocromatina , Hominidae/sangue , Humanos , Masculino , Dados de Sequência Molecular , Técnicas de Amplificação de Ácido Nucleico , Pan paniscus/genética , Pan troglodytes/genética , Filogenia , Reação em Cadeia da Polimerase , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico , Especificidade da Espécie , Telômero/genéticaRESUMO
The structured coalescent describes the ancestral relationship among sampled genes from a geographically structured population. The aim of this article is to apply the central limit theorem to functionals of the migration process to study coalescence times and population structure. An application of the law of large numbers to the migration process leads to the strong migration limit for the distributions of coalescence times. The central limit theorem enables us to obtain approximate distributions of coalescence times for strong migration. We show that approximate distributions depend on the population structure. If migration is conservative and strong, we can define a kind of effective population size N(e)(*), with which the entire population approximately behaves like a panmictic population. On the other hand, the approximate distributions for nonconservative migration are qualitatively different from those for conservative migration. And the entire population behaves unlike a panmictic population even though migration is strong.
Assuntos
Genética Populacional , Modelos Genéticos , Algoritmos , Migração Animal , Animais , Genes/genética , Haploidia , Cadeias de Markov , Mutação/genética , Filogeografia , Densidade Demográfica , Dinâmica Populacional , Fatores de TempoRESUMO
Results of twin studies have shown that autism spectrum disorders (ASDs) are attributable to complex multigenic interactions rather than to a single susceptibility gene. However, the growing number of distinct, individually rare genetic causes of ASDs, mostly copy number variations (CNVs), favors an alternative to the polygenic hypothesis, the two-component model, which suggests that ASDs are caused either by de novo mutation or by dominant inheritance from asymptomatic carriers of such a mutation. To verify this hypothesis, we estimated the distribution of ASD-risk among both catchment area-based families and multiplex families. Our results suggest that the models with more than three risk components are preferable to the two-component model. Our results also suggest that the largest proportion of ASD cases is caused by dominant inheritance. We additionally show that Supplementary information regarding prevalence has a crucial role in analyzing proband-ascertained data.
Assuntos
Algoritmos , Transtornos Globais do Desenvolvimento Infantil/genética , Modelos Genéticos , Pré-Escolar , Saúde da Família , Feminino , Frequência do Gene , Genes Dominantes , Predisposição Genética para Doença , Humanos , Lactente , Masculino , Fatores de Risco , IrmãosRESUMO
The aim of this article is to investigate the distribution of the coalescence time (T) for sampled genes in the structured coalescent. We obtain some exact solutions for small samples and approximate distributions for n sampled genes in strong and weak migration. We also conduct computer simulation to evaluate efficiencies of these approximations and show the dependency of the distribution of the coalescence time on the geographical structure and the intensity of migration. In a panmictic population, we prove that the conditional distribution of the coalescence time given the number of segregating sites (S) among sampled genes is given by the weighted mean of the convolution of gamma distributions. We also study the joint distribution of T and S in the structured coalescent model and show some exact solutions.
