In this review we have attempted to account for the evolution of dimorphic sex chromosomes and to explain the evolution and significance of related phenomena such as the conformational changes with sex chromosomes undergo during meiosis, dosage compensation, and the imprinting of sex chromosomes. The scheme which we have proposed incorporates many of the features of hypotheses which were put forward by Muller (1918), Nei (1969, 1970), Charlesworth (1978), Lucchesi (1978), Bull (1983), Graves (1987) and others to explain the evolution of heteromorphic sex chromosomes. However, unlike these authors, we have stressed the importance in sex chromosome behaviour and evolution of the constraint associated with meiotic pairing. Since the consequences of meiotic pairing failure are a reduction in fitness, mechanisms have evolved which reduce the frequency of pairing failure or counteract its effects. We believe that these mechanisms are responsible either directly or indirectly for many of the changes which have led to the evolution of dimorphic sex chromosomes. They are also involved in the evolution of dosage compensation in some groups, and are probably responsible for the marked genomic imprinting found in the sex chromosomes of some species.
|Number of pages||28|
|State||Published - 1990|