Two sex-reversed males and eight intersexes have been found in a natural population of the mole species Talpa occidentalis. All individuals of karyotype 34,XY were normal males, while the 34,XX karyotype was found in normal females, intersexes and sex-reversed males. Small testes were present in XX males, and ovotestes in intersexes. Intersexes showed male antigen levels higher than for females and lower than for males (including XX males), as judged by cytotoxicity tests. The X chromosome of sex-reversed males and intersexes and the Y chromosome of males appeared morphologically normal.

Standard linkage testing crosses and ovarian teratoma mapping were used to estimate the length of the chromosomal segment that is marked by galactose-1-phosphate uridyl transferase and soluble aconitase and that has been conserved since divergence of lineages leading to mouse and man. These experiments were also used to determine whether the Rb(4·6)2Bnr Robertsonian translocation suppresses recombination on the proximal portion of mouse Chromosome 4. The estimated length of the conserved segment marked by galactose-1-phosphate uridyl transferase and soluble aconitase in mouse and man was estimated to be 24 cM. It was also shown that Rb(4·6)2Bnr strongly suppressed recombination on the centromeric portion of mouse Chromosome 4.

The n0 coalescent of Kingman (1982a, b) describes the family relationships among a sample of n0 individuals drawn from a panmictic species. It is a stochastic process resulting from n0 − 1 independent random events (coalescences) at each of which n (2 ≤ n ≤ n0) ancestral lineages of a sample are descended from n − 1 distinct ancestors for the first time. Here a similar genealogical process is studied for a species consisting of two populations with migration between them. The main interest is with the probability density of the time length between two successive coalescences and the spatial distribution of n − 1 ancestral lineages over two populations when n to n − 1 coalescence takes place. These are formulated based on a non-linear birth and death process with killing, and are used to derive several explicit formulae in selectively neutral population genetics models. To confirm and supplement the analytical results, a simulation method is proposed based on the underlying bivariate Markov chain. This method provides a general way for solving the present problem even when an analytical approach appears very difficult. It becomes clear that the effects of the present population structure are most conspicuous on 2 to 1 coalescence, with lesser extents on n to n − 1 (3 ≤ n) coalescence.This implies that in a more general model of population structure, the number of populations and the way in which a sample is drawn are important factors which determine the n0 coalescent.

A population genetics model of the role of asymmetric pairing and unequal exchange in the stabilization of transposable element copy number in natural populations is proposed and analysed. Monte Carlo simulations indicate that the approximations incorporated into the analysis are robust in the relevant parameter ranges. Given several simple assumptions concerning transposition and excision, equal and unequal exchange, and chromosome structure, predictions of the relative numbers of transposable elements in various regions of the Drosophila melanogaster genome are compared to the observed distribution of roo/B104 elements across chromosomal regions with differing rates of exchange, and between X chromosomes and autosomes. There is no indication of an accumulation of elements in the distal regions of chromosomes, which is expected if unequal exchange is reduced concomitantly with normal crossing over in the distal regions. There is, however, an indication of an excess of elements relative to physical length in the proximal regions of the chromosomes, which also have restricted crossing over. This observation is qualitatively consistent with the model's predictions. The observed distribution of elements between the mid-sections of the X chromosomes and autosomes is consistent with the predictions of one of two models of unequal exchange.

The extent of accumulation of mouse Y chromosomal repetitive sequences generally correlates with the known phylogenetic relationships in the genus Mus. However, we describe here a M. musculus Y chromosomal repetitive sequence, designated as ACClfl, whose accumulation patterns among eight Mus species do not correspond to their phylogenetic relationships. Although male-specific hybridization bands were present in all the species examined, significant accumulation (> 200 copies) in the Y chromosomes was found in M. minutoides (subgenus Nannomys), M. pahari (subgenus Coelomys) and M. saxicola (subgenus Pyromys) as well as in the three closely related species M. hortulanus, M. musculus and M. spretus that belong to the subgenus Mus. Unexpectedly, the Y chromosomes of M. caroli and M. cookii (both subgenus Mus) had considerably reduced amounts of ACClfl-related sequences. Furthermore, in rats (Rattus norvegicus) the major accumulation sites appear to be autosomal. These observations suggest that caution must be taken in the interpretation of data obtained with repetitive sequences that have evolved quickly.

There are a number of reports of gametic disequilibrium between alleles causing segregation distortion (e.g. t alleles in M. musculus and SD alleles in D. melanogaster) and linked loci. These observations have resulted in the conclusion by some researchers that segregation distortion may cause gametic disequilibrium. In this manuscript I have shown that (1) segregation distortion cannot generate gametic disequilibrium de novo and (2) because segregation distortion results in an excess of heterozygotes, the rate of decay of disequilibrium is faster than if segregation distortion were absent. Other factors, such as mutation or selection, appear to generate the observed disequilibrium, and extremely low recombination appears important in retarding its decay.

Age-related reactivation of an X-linked gene which maps close to Xce, the X chromosome inactivation centre, has been observed. In five female mice which carried the X-linked coat colour gene Moblo on the reciprocal translocation T(X;16)16H (Searle's translocation), and the wild-type gene on the normal X chromosome, and therefore expressed the Moblo phenotype due to the non-random inactivation characteristic of Searle's translocation, progressive darkening of the coat was observed as the animals aged. This is due to reactivation of the previously inactivated wild-type gene at the Mo locus on the normal X chromosome. As the Mo locus is located 4 cM distal to Xce, the X chromosome inactivation centre, these observations provide evidence of age-related instability of inactivation of an X-linked gene close to the inactivation centre.