The human X chromosome has a unique biology that was shaped by its evolution as the sex chromosome shared by males and females. We have determined 99.3% of the euchromatic sequence of the X chromosome. Our analysis illustrates the autosomal origin of the mammalian sex chromosomes, the stepwise process that led to the progressive loss of recombination between X and Y, and the extent of subsequent degradation of the Y chromosome. LINE1 repeat elements cover one-third of the X chromosome, with a distribution that is consistent with their proposed role as way stations in the process of X-chromosome inactivation. We found 1,098 genes in the sequence, of which 99 encode proteins expressed in testis and in various tumour types. A disproportionately high number of mendelian diseases are documented for the X chromosome. Of this number, 168 have been explained by mutations in 113 X-linked genes, which in many cases were characterized with the aid of the DNA sequence.

This paper provides a survey of`first wave' economic studies of tropical deforestation and land use. These studies of tropical forest land conversion are generally at the cross-country level. We also conduct a synthesis cross-country analysis of tropical agricultural land expansion. The results show that agricultural development is the main factor determining land expansion, but institutional factors have an important influence. Income effects tend to vary from region to region, and do not always display an`Environmental Kuznets Curve' relationship.This paper also provides a review of the more recent`second wave' economic studies of tropical deforestation that model and analyze the economic behaviour of agricultural households, timber concessionaires and other agents within tropical forest countries who affect deforestation through their land use decisions. Further work in this area requires more country-level and local case studies into tropical deforestation and land use.

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