Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (M.A.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 38-42). Also available on the Internet.

Thesis (M.A.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 138-144).

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 104-116). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (M.A.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 38-42). Also available on the Internet.

Introdução: Embora o nascimento de gêmeos tenha sempre chamado atenção, não há fatores genéticos ou ambientais conhecidos que podem determinar o nascimento de monozigóticos gêmeos (MZ). E mesmo para gêmeos dizigóticos (DZ), influências genéticas não são completamente compreendidas. Objetivos: Um estudo prévio do nosso grupo demonstrou que o alelo C do polimorfismo rs1042522 no gene TP53 foi mais frequente nas mães de gêmeos do que nas mães de gestação única em uma pequena cidade no sul do Brasil. A fim de esclarecer se este foi um fator isolado, foi realizado um estudo observacional de caso-controle de base populacional. Métodos: As amostras foram selecionadas a partir de um programa de investigação de paternidade financiado pelo estado do Rio grande do Sul. As amostras foram consideradas casos em que duas das crianças tinham a mesma data de nascimento e os controles eram de amostras em que pelo menos dois filhos nasceram em datas diferentes. O método de escolha dos controles foi sequencial, sendo utilizados os primeiros que preenchessem esta condição a cada ano. Resultados: De 2007 a 2013, foram 32.661 registros pesquisados e 283 (0,9%) gêmeos foram encontrados (119 MZ e 164 DZ). Frequências alélicas e genotípicas não foram diferentes entre as mães de gêmeos ou mães de não gêmeos. No entanto, as mães de gêmeos MZ apresentaram uma maior frequência do genótipo GG e menor frequência do alelo C quando comparado com as mães de gêmeos DZ. Além disso, a proporção de gêmeos monozigóticos (42%) é maior do que normalmente relatado (30%). Finalmente, a proporção de gêmeos encontrados neste estudo parece ser mais realista, já que esta amostra não é supostamente de usuárias de técnicas de reprodução assistida. / Introduction: Although the birth of twins has always attracted attention, there are no known genetic or environmental factors that can determine the birth of monozygotic (MZ) twins. And even for dizygotic (DZ) twins, genetic influences are not completely understood. Objective: A previous study from our group has shown that the C allele of polymorphism rs1042522 in TP53 gene was more frequent in the mothers of twins than in the mothers of singletons in a small village in South Brazil. In order to clarify if this was an isolated factor, we performed a population-based observational case-control study. Methods: Samples were selected from a state-funded program of paternity investigation. Samples were considered cases when two of the children had the same date of birth whereas controls were those samples in which at least two children were born in different dates. The first subsequent sample fulfilling control criteria was included after each case. Results: From 2007 to 2013, 32,661 records were searched and 283 (0.9%) twins were found (119 MZ and 164 DZ). Genotypic and allele frequencies were not different between mothers of twins or mothers of singletons. However, mothers of MZ twins showed a higher frequency of GG genotype and lower frequency of the C allele when compared to mothers of DZ twins. Also, the proportion of MZ twins (42%) is higher than usually reported (30%). Finally, the proportion of twins found in this study seems to be more realistic, as this sample is allegedly not user of assisted reproduction techniques.

The purpose of this study is to examine instances of naturally occurring conversations between twin siblings. This study uses both conversation analysis and semi-structured interviews to investigate communication patterns and practices in everyday twin-to-twin talk. The following research questions guided this study: (1) What pragmatic features of analytic interest are present in twin-to-twin talk? (2) What pragmatic features of analytic interest are present when twins interact with other members of the family system? There were a total of six sets of twin siblings between the ages of 10 and 15 who engaged in participant self-taping and semi-structured interviews. Although it did not have an observable effect on the findings, there were five sets of dizygotic (fraternal) twins and one set of monozygotic (identical) twins. Eight parents were interviewed and four parents participated in the conversations with the twin siblings. Findings suggest that certain communication practices and Phenomena are present in twin siblings' conversations, though not necessarily uniquely. Simultaneous speech is a conversational practice evident in every set of twin siblings' transcripts, serving as a completion to the other's utterance. In the presence of parents, it functions as a competitive move, other-initiated repair, and entertainment. As the twins conversed alone, extension/completion of the other twin's utterance served as a way to verify reported speech. It functions as support, verification, competition, and a way to gain attention when talking in front of a parent. The joint conversational performance act of code-switching was a practice used for entertainment by the twins when conversing alone. It served as a way to prove a point and to entertain as they interacted with a parent. Conversational phenomena included testing, and speaking for one's twin. Twins engaged in testing while conversing alone to show support for their twin. As they engaged in talk with a parent present, it served as competition/support, role confirmation/enactment, and identification/deidentification between the twin siblings. Speaking for one's twin could only occur while the twins were conversing in front of a parent. It functioned as a competitive move, as support, and as a way to gain attention.

This study explored the potential impact of child temperament and daycare on behavior problems and parental sensitivity. It was expected that children with more "difficult" temperaments would exhibit more behavior problems and have less sensitive parents when experiencing high amounts of daycare. Measures from 60 families involved in the Southern Illinois Twins and Siblings Study (SITSS) were examined. Results indicated that highly active children exhibited more externalizing behaviors when experiencing less daycare. Shy children experiencing more daycare had more sensitive parents. Additionally, a temperamental difference between co-twins was related to differential parental sensitivity. Lastly, DZ co-twins were more temperamentally different when experiencing high amounts of daycare. These results demonstrate that daycare does seem to affect children; however, the specific effect depends on the child's temperament. Additionally, temperament is an important factor when examining parental sensitivity shown to twins and when determining how MZ and DZ twins react to daycare.

This study examined the development of social cognition in children with and without autism spectrum disorder (ASD), as well as the influence of behavioral and molecular genetics on these higher-order cognitive abilities. Specifically, it was hypothesized that children with ASD would perform more poorly on all social cognitive tasks compared with typically developing peers. In addition, it was hypothesized that typically developing children who performed better on a simpler social cognitive task at ages 3 or 4 would perform better at follow-up (i.e., one time between the ages of 6-10). Lastly, it was hypothesized that children who had at least one risk allele in both the DRD4 and the 5-HTTLPR polymorphisms would perform worse than those who had at least one risk allele in either polymorphism, who, in turn, would perform worse than children without any risk alleles. The twin sample included 62 families of multiples (twins, triplets, or quadruplets) who were recruited through the Southern Illinois Twins and Siblings Study (SITSS), and the ASD sample included 25 children who were recruited from the Center for Autism Spectrum Disorders at SIU. Significant group differences were found for children's performance on all of the social cognitive tasks. Furthermore, results showed that some areas of social cognition (theory of mind and the understanding of non-literal language) are more influenced by genetic factors than are other cognitive skills. Lastly, results from the molecular genetic analyses suggest that basic social cognitive skills (e.g., theory of mind) may be influenced by underlying biological factors in the serotonergic and dopaminergic pathways. The present study provided useful information on how psychological and genetic factors influence the development of social cognitive abilities in children with and without ASD.