Population structure of the human pseudoautosomal boundary

Article Abstract:

Sex chromosomes consist of two X chromosomes in females, and one X and one Y chromosome in males. The sex chromosomes in mammals contain two distinct regions: the pseudoautosomal region, where exchange of genetic material between the X and Y chromosomes takes place, and regions that are specific to only one sex. Between the two regions, there is an insertion of a particular sequence of deoxyribose nucleic acid (DNA), known as the Alu element. This boundary region was examined for differences in DNA sequences in 57 Y chromosomes and 60 X chromosomes obtained from 10 human populations from various regions including Africa, Australia, Europe, and Japan. The X chromosome was polymorphic, and had sequence differences in five areas in a 300 nucleotide boundary region. The Y chromosomes were identical except for one region which was also polymorphic in the X chromosomes. This evidence supports theoretical predictions that the X chromosome has more variation than the Y chromosome. It is thought that the boundary region of the human X chromosome has descended from two chromosomes with independent early histories, while the boundary regions of the Y chromosome is derived from chromosomes that developed much later. The polymorphisms are probably due to a variety of evolutionary factors including mutation, selection, recombination, and population structure and drift. These studies provide insight into the evolution of man and could be used to examine the migration patterns of man throughout the world. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evolution (Biology), Evolution, X chromosome, Sex chromosomes, Primitive societies, Traditional societies

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For our eyes only

Article Abstract:

The removal of the tumor-suppressor gene for retinoblastoma in mouse embryos causes death in utero to occur at about embryonic day 12 or 13. Three research groups consisting of Eva Y.-H.P. Lee and colleagues, Tyler Jacks and colleagues and Alan R. Clarke and colleagues found that death resulted from the inhibition of correct cell differentiation especially in the central nervous system and erythrocytes. This finding confirms that the deletion of tumor-suppressor genes can have lethal consequences.

Genetic aspects, Tumor suppressor genes, Retinoblastoma

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Big genes and little genes and deadlines for transcription

Article Abstract:

Fly embryos of the genus Drosophila have fast mitotic cycles that set deadlines for genetic transcription that are impossible for larger genes to meet. M. Rothe and colleagues found that these cell cycles thus prevent the premature expression of large genes by functioning as a biological 'gene screen.' This delaying of the larger genes' expression is necessary because it keeps the cells from undergoing mitosis before the RNA polymerase can finish the often protracted work of transcribing a gene.

Genetic regulation, Genetic transcription, Transcription (Genetics)

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