Context and question: The rhythm is linked to the lightdark cycle. Animals, including humans, kept in total darkness for extended periods eventually function with a free-running rhythm. Their sleep cycle is pushed back or forward each "day", depending on whether their "day", their endogenous period, is shorter or longer than 24 hours. The environmental cues that reset the rhythms each day are called zeitgebers (from the German, "time-givers"). Totally blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clocks in the apparent absence of external stimuli. Although they lack image-forming eyes, their photoreceptors (which detect light) are still functional; they do surface periodically as well.[page needed]
What kind of mammals need external stimuli to maintain their endogenous clock?
Answer: unanswerable
Context and question: According to the 2002 Census, 4.6% of the Chilean population, including the Rapanui (a Polynesian people) of Easter Island, was indigenous, although most show varying degrees of mixed heritage. Many are descendants of the Mapuche, and live in Santiago, Araucania and the lake district. The Mapuche successfully fought off defeat in the first 300350 years of Spanish rule during the Arauco War. Relations with the new Chilean Republic were good until the Chilean state decided to occupy their lands. During the Occupation of Araucania the Mapuche surrendered to the country's army in the 1880s. Their land was opened to settlement by Chileans and Europeans. Conflict over Mapuche land rights continues to the present.
When did the Mapuche surrender to the Chilean army?
Answer: 1880s
Context and question: The majority of eukaryotic genes are stored on a set of large, linear chromosomes. The chromosomes are packed within the nucleus in complex with storage proteins called histones to form a unit called a nucleosome. DNA packaged and condensed in this way is called chromatin.:4.2 The manner in which DNA is stored on the histones, as well as chemical modifications of the histone itself, regulate whether a particular region of DNA is accessible for gene expression. In addition to genes, eukaryotic chromosomes contain sequences involved in ensuring that the DNA is copied without degradation of end regions and sorted into daughter cells during cell division: replication origins, telomeres and the centromere.:4.2 Replication origins are the sequence regions where DNA replication is initiated to make two copies of the chromosome. Telomeres are long stretches of repetitive sequence that cap the ends of the linear chromosomes and prevent degradation of coding and regulatory regions during DNA replication. The length of the telomeres decreases each time the genome is replicated and has been implicated in the aging process. The centromere is required for binding spindle fibres to separate sister chromatids into daughter cells during cell division.:18.2
Chromosomes that are packed within the nucleus in complex with histones are called what?
Answer:
a nucleosome