Two silkworm strains viz, B20 A (high cocoon shell ratio) and C.Nichi (low cocoon shell ratio) were sib mated for 10 generations to determine the homozygosis. Both bulked segregant analysis(BSA) and near isogenic line...Two silkworm strains viz, B20 A (high cocoon shell ratio) and C.Nichi (low cocoon shell ratio) were sib mated for 10 generations to determine the homozygosis. Both bulked segregant analysis(BSA) and near isogenic lines (NIL) studies were done to identify the RFLP markers closely linked to cocoon shell parameters. Three hundred and fifty two random clones were identified as the low copy number sequence and used for identification of Restriction Fragment Length Polymorphic (RFLP) marker linked to cocoon weight and cocoon shell character. In the bulk segregant analysis, DNA from the parents (B20 A, C.Nichi), F 1 and F 2 progeny of high shell ratio (HSR) and low shell ratio (LSR) were screened for hybridization with the random clones. Polymorphic banding pattern achieved through southern hybridization with different probes indicated the probable correlation of polymorphism with high and low cocoon shell character which are possible landmarks in identifying the putative marker(s) for the cocoon shell character. Out of the 100 probes tried with parents, F 1, F 2 and their bulks, 10 probes were found to be closely linked to cocoon shell characters.展开更多
The causes of population differentiation can provide insight into the origins of early barriers to gene flow. Two key drivers of population differentiation are geographic distance and local adaptation to divergent sel...The causes of population differentiation can provide insight into the origins of early barriers to gene flow. Two key drivers of population differentiation are geographic distance and local adaptation to divergent selective environments. When reproductive isolation arises because some populations of a species are under selection to avoid hybridization while others are not, population differentiation and even speciation can result. Spadefoot toad populations Spea multiplicata that are sympatric with a congener have undergone reinforcement. This reinforcement has resulted not only in increased reproductive isolation from the congener, but also in the evolution of reproductive isolation from nearby and distant conspecific allopatric populations. We used multiple approaches to evaluate the contributions of geographic distance and divergent selective environments to population structure across this regional scale in S. multiplicata, based on genotypes from six nuclear microsatellite markers. We compared groups of populations varying in both geographic location and in the presence of a congener. Hierarchical F-statistics and results from cluster analyses and discriminant analyses of principal components all indicate that geographic distance is the stronger contributor to genetic differentiation among S. multiplicata populations at a regional scale. However, we found evidence that adaptation to divergent selective environments also contributes to population structure. Our findings highlight how variation in the balance of evolutionary forces acting across a species＇ range can lead to variation in the relative contributions of geographic distance and local adaptation to population differentiation across different spatial scales.展开更多
Speciation research has seen a renewed interest in ecological speciation, which emphasises divergent ecological se- lection leading to the evolution of reproductive isolation. Selection from divergent ecologies means ...Speciation research has seen a renewed interest in ecological speciation, which emphasises divergent ecological se- lection leading to the evolution of reproductive isolation. Selection from divergent ecologies means that phenotypic plasticity can play an important role in ecological speciation. Phenotypic plasticity involves the induction of phenotypes over the lifetime of an organism and emerging evidence suggests that epigenetic marks such as cytosine and protein （histone） modifications might regu- late such environmental induction. Epigenetic marks play a wide role in a variety of processes including development, sex dif- ferentiation and allocation, sexual conflict, regulation of transposable elements and phenotypic plasticity. Here we describe recent studies that investigate epigenetic mechanisms in a variety of contexts. There is mounting evidence for environmentally induced epigenetic variation and for the stable inheritance of epigenetic marks between generations. Thus, epigenetically-based pheno- typic plasticity may play a role in adaptation and ecological speciation. However, there is less evidence for the inheritance of in- duced epigenetic variation across multiple generations in animals. Currently few studies of ecological speciation incorporate the potential for the involvement of epigenetically-based induction of phenotypes, and we argue that this is an important omission [Current Zoology 59 （5）： 686-696, 2013 ].展开更多
文摘Two silkworm strains viz, B20 A (high cocoon shell ratio) and C.Nichi (low cocoon shell ratio) were sib mated for 10 generations to determine the homozygosis. Both bulked segregant analysis(BSA) and near isogenic lines (NIL) studies were done to identify the RFLP markers closely linked to cocoon shell parameters. Three hundred and fifty two random clones were identified as the low copy number sequence and used for identification of Restriction Fragment Length Polymorphic (RFLP) marker linked to cocoon weight and cocoon shell character. In the bulk segregant analysis, DNA from the parents (B20 A, C.Nichi), F 1 and F 2 progeny of high shell ratio (HSR) and low shell ratio (LSR) were screened for hybridization with the random clones. Polymorphic banding pattern achieved through southern hybridization with different probes indicated the probable correlation of polymorphism with high and low cocoon shell character which are possible landmarks in identifying the putative marker(s) for the cocoon shell character. Out of the 100 probes tried with parents, F 1, F 2 and their bulks, 10 probes were found to be closely linked to cocoon shell characters.
文摘The causes of population differentiation can provide insight into the origins of early barriers to gene flow. Two key drivers of population differentiation are geographic distance and local adaptation to divergent selective environments. When reproductive isolation arises because some populations of a species are under selection to avoid hybridization while others are not, population differentiation and even speciation can result. Spadefoot toad populations Spea multiplicata that are sympatric with a congener have undergone reinforcement. This reinforcement has resulted not only in increased reproductive isolation from the congener, but also in the evolution of reproductive isolation from nearby and distant conspecific allopatric populations. We used multiple approaches to evaluate the contributions of geographic distance and divergent selective environments to population structure across this regional scale in S. multiplicata, based on genotypes from six nuclear microsatellite markers. We compared groups of populations varying in both geographic location and in the presence of a congener. Hierarchical F-statistics and results from cluster analyses and discriminant analyses of principal components all indicate that geographic distance is the stronger contributor to genetic differentiation among S. multiplicata populations at a regional scale. However, we found evidence that adaptation to divergent selective environments also contributes to population structure. Our findings highlight how variation in the balance of evolutionary forces acting across a species＇ range can lead to variation in the relative contributions of geographic distance and local adaptation to population differentiation across different spatial scales.
文摘Speciation research has seen a renewed interest in ecological speciation, which emphasises divergent ecological se- lection leading to the evolution of reproductive isolation. Selection from divergent ecologies means that phenotypic plasticity can play an important role in ecological speciation. Phenotypic plasticity involves the induction of phenotypes over the lifetime of an organism and emerging evidence suggests that epigenetic marks such as cytosine and protein （histone） modifications might regu- late such environmental induction. Epigenetic marks play a wide role in a variety of processes including development, sex dif- ferentiation and allocation, sexual conflict, regulation of transposable elements and phenotypic plasticity. Here we describe recent studies that investigate epigenetic mechanisms in a variety of contexts. There is mounting evidence for environmentally induced epigenetic variation and for the stable inheritance of epigenetic marks between generations. Thus, epigenetically-based pheno- typic plasticity may play a role in adaptation and ecological speciation. However, there is less evidence for the inheritance of in- duced epigenetic variation across multiple generations in animals. Currently few studies of ecological speciation incorporate the potential for the involvement of epigenetically-based induction of phenotypes, and we argue that this is an important omission [Current Zoology 59 （5）： 686-696, 2013 ].
