7 The Proterminal Regions and Telomeres of Human Chromosomes

Abstract

This chapter discusses the proterminal regions and telomeres of human chromosomes. The chapter also discusses recent advances in the description of terminal sequences of human chromosomes and relates them to the known and proposed functions of telomeres and proterminal regions. The rapid turnover of terminal sequences of human chromosomes in somatic tissues during evolution is discussed in the chapter. Chromosome abnormalities that involve the loss or rearrangement of terminal sequences and contribute to the generation of some contiguous gene syndromes are also considered in the chapter. In situ hybridization studies have shown that the telomere repeats lie close to the nuclear membrane and tightly associated with the nuclear matrix throughout interphase in many different human cell types. In some cell types of some species, chromosomes adopt a “Rabl” orientation where the telomeres become arranged near one another and near to the nuclear membrane, while the centromeres tend to associate on the opposite side of the nucleus. It is also thought that telomeres are directly involved in terminal associations sometimes observed between homologous and nonhomologous chromosomes. The extent to which cryptic terminal rearrangements of human chromosomes contribute to genetic disease is yet to be determined.