Studies of Y chromosome evolution often emphasize gene loss, but this loss has been counterbalanced by addition of new genes. The DAZ genes, which are critical to human spermatogenesis, were acquired by the Y chromosome in the ancestor of Old World monkeys and apes. We and our colleagues recently sequenced the rhesus macaque Y chromosome, and comparison of this sequence to human and chimpanzee enables us to reconstruct much of the evolutionary history of DAZ. We report that DAZ arrived on (...) the Y chromosome about 38 million years ago via the transposition of at least 1.1 megabases of autosomal DNA. This transposition also brought five additional genes to the Y chromosome, but all five genes were subsequently lost through mutation or deletion. As the only surviving gene, DAZ experienced extensive restructuring, including intragenic amplification and gene duplication, and has been the target of positive selection in the chimpanzee lineage.Editor's suggested further reading in BioEssays Should Y stay or should Y go: The evolution of non‐recombining sex chromosomes Abstract. (shrink)

Das historische Buch konnen zahlreiche Rechtschreibfehler, fehlende Texte, Bilder, oder einen Index. Kaufer konnen eine kostenlose gescannte Kopie des Originals durch den Verlag. 1907. Nicht dargestellt. Auszug:... I. TEIL DIE PROBLEME DER GRUNDWISSENSCHAFT ndem wir nunmehr an die von uns zu behandelnde Wissenschaft herantreten, gilt es zunachst uns klar zu werden uber die Fragen, uber die wir eine Entscheidung zu treffen haben. Es sind zum Teil solche, uber welche die Denker vor uns abweichende Ansichten geaussert haben; wir mussen aber auch (...) an etwaige weitere denken, die sie ubersehen haben mochten. Wer einer Sache recht auf den Grund kommen will, fur den ist das erste Erfordernis dies, dass er den Problemen scharf ins Gesicht sehe. Denn die nachher zu erlangende Einsicht hangt an der Losung der vorher ins Auge gefassten Probleme; wer den Knoten nicht kennt, der kann ihn auch nicht losen. Solch ein Knoten in dem Objekte aber ist es, den das Problem darstellt, wie es sich fur das Nachdenken auftut. Dem Denken namlich, sofern es die Schwierigkeit gewahr wird, ergeht es ganz ahnlich wie den Leuten, die sich durch einen festen Knoten eingeschnurt fuhlen: beide konnen keinen Schritt vorwarts tun. Darum ist es notig, zuvorderst alle Schwierigkeiten ins Auge gefasst zu haben; ist es schon aus diesem Grunde geboten, so ist ein weiterer Grund der, dass man, wenn man ohne diese Erwagung der Probleme an die Untersuchung herantritt, dem Wanderer gleicht, der nicht weiss, wohin er seinen Weg zu richten hat; und dass man ausserdem im andern Fall nicht einmal, wenn man etwas gefunden hat, zu erkennen imstande ware, ob das Gefundene auch das ist, was man sucht, oder nicht. Denn in jenem Fall ist das Ziel nicht klar; wohl aber ist es dem klar, der zuvor die Probleme sich zum Bewusstsein gebracht hat. Daz. (shrink)

Spermatogenesis is an elaborate process involving both cell division and differentiation, and cell‐cell interactions. Defects in any of these processes can result in infertility, and in some cases these can be genetic in cause. Mapping experiments have defined at least three regions of the human Y chromosome that are required for normal spermatogenesis. Two of these contain the genes encoding the RNA binding proteins RBM and DAZ, suggesting that the control of RNA metabolism is likely to be an important control (...) point for human spermatogenesis. A similar analysis in mice has shown that at least two regions of the mouse Y chromosome are essential for spermatogenesis. Both genetic and reverse genetic approaches have been used to identify mouse autosomal genes required for spermatogenesis. These studies have shown that genes in a number of different pathways are essential for normal spermatogenesis, and also provide putative models of human infertility. (shrink)

In this paper we investigate whether timing in monolingual acquisition interacts with age of onset and input effects in child bilingualism. Six different morpho-syntactic and semantic phenomena acquired early, late or very late are considered, with their timing in L1 acquisition varying between age 3 (subject-verb agreement) and after age 6 (case marking). Data from simultaneous bilingual children (2L1) whose mean age of onset to German was three months are compared with data from early second language learners of German (eL2) (...) whose mean age of onset to German was 35 months as well as with data from monolingual children. To explore change over time, children were tested twice at the ages of 4;4 years and 5;8 years. The main findings were that 2L1 children had an advantage over their eL2 peers in early acquired phenomena, which disappeared with time, whereas in late acquired phenomena 2L1 and eL2 children did not differ. Moreover, 2L1 children performed like monolingual children in early acquired phenomena but had a disadvantage in the late acquired phenomena with the amount of delay decreasing with time. We conclude that age of onset effects are modulated by effects of timing in monolingual acquisition. Contrary to expectation, input in terms of language dominance, measured as the dominant language used at home, did not affect simultaneous bilingual children’s performance in any of the phenomena. We discuss the implications of our findings for the hypothesis that acquisition of late phenomena is determined by input alone and suggest an alternative concept: the learner’s internal need for time to master a phenomenon, which is determined by its complexity and cross-linguistic robustness. (shrink)