Sex-specific differences in the synaptonemal complex in the genus Oreochromis (Cichlidae)

Total synaptonemal complex (SC) lengths were estimated from Oreochromis aureus Steindachner (which has a WZ/ZZ sex determination system), O. mossambicus Peters and O. niloticus L. (both of which have XX/XY sex determination systems). The total SC length in oocytes was greater than that in spermatocytes in all three species (194±30 μm and 134±13 μm, 187±22 μm and 127±17 μm, 193±37 μm and 144±19 μm, respectively). These sex-specific differences did not appear to be influenced by the type of sex determination system (the female/male total SC length ratio was 1.45 in O. aureus, 1.47 in O. mossambicus and 1.34 in O. niloticus) and do not correlate with the lack of any overall sex-specific length differences in the current Oreochromis linkage map. Although based on data from relatively few species, there appears to be no consistent relationship between sex-specific SC lengths and linkage map lengths in fish. Neomale (hormonally masculinized genetic female) O. aureus and O. mossambicus had total SC lengths of 138±13 μm and 146±13 μm respectively, more similar to normal males than to normal females. These findings agree with data from other vertebrate species that suggest that phenotypic sex, rather than genotype, determines traits such as total SC length, chiasmata position and recombination pattern, at least for the autosomes

Genome-Wide Crossover Distribution in Arabidopsis thaliana Meiosis Reveals Sex-Specific Patterns along Chromosomes

In most species, crossovers (COs) are essential for the accurate segregation of homologous chromosomes at the first meiotic division. Their number and location are tightly regulated. Here, we report a detailed, genome-wide characterization of the rate and localization of COs in Arabidopsis thaliana, in male and female meiosis. We observed dramatic differences between male and female meiosis which included: (i) genetic map length; 575 cM versus 332 cM respectively; (ii) CO distribution patterns: male CO rates were very high at both ends of each chromosome, whereas female CO rates were very low; (iii) correlations between CO rates and various chromosome features: female CO rates correlated strongly and negatively with GC content and gene density but positively with transposable elements (TEs) density, whereas male CO rates correlated positively with the CpG ratio. However, except for CpG, the correlations could be explained by the unequal repartition of these sequences along the Arabidopsis chromosome. For both male and female meiosis, the number of COs per chromosome correlates with chromosome size expressed either in base pairs or as synaptonemal complex length. Finally, we show that interference modulates the CO distribution both in male and female meiosis

The Performance of Exchange Rate Forecasts

Since the floating of the Australian dollar the forecasting of exchange rate movements has become more difficult and received much more attention. As a result, some participants in the foreign exchange market have, on a number of occasions, come under criticism for their inability to predict exchange rate movements. This article seeks to evaluate these criticisms through an examination of exchange rate forecasts made by market participants (as published in the Australian Financial Review from March 1985 to December 1985). The accuracy of the $A/US$ forecasts is compared with that of forecasts generated from a number of simple forecasting rules as well as forecasts of the US$/Yen exchange rate. In general, the simple forecasting rules provide superior forecasts to those provided by the individual market participants. However, under some criteria, the mean of the individual participants' forecasts may be preferred to these simple forecasting rules. Further, the comparison of the US$/Yen forecasts with the $A/US$ forecasts shows the former to be generally more accurate. Copyright 1987 The University of Melbourne, Melbourne Institute of Applied Economic and Social Research.

Rational expectations in European economies

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