Recurrent horizontal transfer identifies mitochondrial positive selection in a transmissible cancer.

Autonomous replication and segregation of mitochondrial DNA (mtDNA) creates the potential for evolutionary conflict driven by emergence of haplotypes under positive selection for 'selfish' traits, such as replicative advantage. However, few cases of this phenomenon arising within natural populations have been described. Here, we survey the frequency of mtDNA horizontal transfer within the canine transmissible venereal tumour (CTVT), a contagious cancer clone that occasionally acquires mtDNA from its hosts.

Facilitators and barriers to the delivery of school-based smoking prevention interventions for children and young people: a protocol for a systematic review of qualitative studies.

Background: Despite a decline in child and adult smoking prevalence, young people who smoke (even occasionally) can rapidly become addicted to nicotine, with most adult smokers initiating smoking before they are 18. Schools have long been a popular setting to deliver youth smoking prevention interventions, but evidence of the effectiveness of school-based prevention programmes is mixed, and outcomes vary by the type of programme delivered. Existing systematic reviews that explore the factors contributing to the success or failure of school-based smoking prevention programmes often exclude qualitative studies, due to a focus on intervention effectiveness which qualitative research cannot answer.