Abstract House mice offer a powerful system for dissecting the genetic basis of phenotypes that isolate species in the early stages of speciation.
Mapping and molecular genetic studies indicate that both are the result of mutations in the huge gene that encodes dystrophin, also symbolized DMD. Approximately two-thirds of the mutations in both forms are deletions of one or many exons in the dystrophin gene.
Although there is no clear correlation found between the extent of the deletion and the severity of the disorder, DMD deletions usually result in frameshift. The mean age at DMD diagnosis was 4.
In this cohort, death occurred at a median age of 17 years. The authors commented that the diagnosis of DMD is being made at an earlier age but survival has not changed. The bulbar extraocular muscles are spared but the myocardium is affected.
There is massive elevation of creatine kinase levels in the blood, myopathic changes by electromyography, and myofiber degeneration with fibrosis and fatty infiltration on muscle biopsy. The onset of Duchenne muscular dystrophy usually occurs before age 3 years, and the victim is chairridden by age 12 and dead by age The onset of Becker muscular dystrophy is often in the 20s and 30s and survival to a relatively advanced age is frequent.
Moser and Emery found that some female heterozygotes had myopathy resembling autosomal recessive limb-girdle muscular dystrophy Serum creatine kinase was particularly elevated in these patients.
In most populations, the frequency of manifesting heterozygotes is about the same as that of females with limb-girdle muscular dystrophy. Soloway and Mudge remarked that patients with advanced muscular dystrophy may develop hypokalemia from insults vomiting, diarrhea, diuretics that would have little effect on normal persons.
Reduced intracellular potassium stores are responsible for this perilous situation, which may be the mechanism of death.
In an Italian boy with congenital myopathy, born to nonconsanguineous parents, Prelle et al. Although the patient showed severe mental retardation, there was no cerebral atrophy.
Cardiomyopathy was also present.
Genomic analysis of the AQP4 gene revealed no abnormalities. The authors concluded that the reduced mRNA was due to either decreased transcription or increased degradation of the message.
There was increased expression of genes related to immune response, sarcomere, extracellular matrix proteins, and signaling or cell growth. Upregulation of these genes reflected dystrophic changes, myofiber necrosis, inflammation, and muscle regeneration.
Genes related to muscle homeostasis and energy metabolism were downregulated. Severe cardiomyopathy did not develop before age 21 in BMD and few patients showed any cardiac signs before age 13 Nigro et al.
They reported 2 carriers with dilated cardiomyopathy and increased serum CK but no symptoms of muscle weakness. Heart biopsies in both patients showed absence of dystrophin in many muscle fibers.
Smooth Muscle Noting that in DMD functional impairment of smooth muscle in the gastrointestinal tract can cause acute gastric dilatation and intestinal pseudoobstruction that may be fatal, Barohn et al.Vol.
62, No. 1, Jan., Published by: Society for the Study of Evolution. Asymmetry and Polymorphism of Hybrid Male Sterility during the Early Stages of Speciation in House Mice. Asymmetry and Polymorphism of Hybrid Male Sterility during the Early Stages of Speciation in House Mice.
Second, in some crosses hybrid male sterility was asymmetric and depended on the species origin of the X chromosome.
These observations confirm and extend previ-ous findings, underscoring the central role that the M. musculus X chromosome plays in reproductive isolation. Hybrid sterility contributes to speciation by restricting gene flow between related taxa.
Although four hybrid sterility genes have been identified in Drosophila and mouse so far, the underlying molecular mechanisms are largely unknown. We describe extensive asynapsis of chromosomes in male and.
found signiﬁcantly smaller testes and fewer sperm in hybrid male progeny of most crosses. Second, in some crosses hybrid male sterility was asymmetric and depended on the species origin of the X . One of the most striking aspects of our data was the strong asymmetry in hybrid male sterility in reciprocal crosses between musculus PWK and either M.
architecture of the polymorphism for hybrid male sterility (HMS) in the F common occurrence of asymmetry  and/or Haldane’s Rule. While the genetic dissections of incompatibility phenotypes by backcrosses and introgression [10,21,24,26,27] have contributed. Regardless, the observation of polymorphism at multiple loci that have a large impact on F 1 hybrid fertility suggests that resolving the overall genetic architecture of hybrid male sterility may require considerable population-level sampling within both M. musculus and M. domesticus (Vyskocilová et al. ). The unexpected combination of genetic . how to cite. good, j. m., handel, m. a. and nachman, m. w. (), asymmetry and polymorphism of hybrid male sterility during the early stages of speciation in house.
domesticus strain (Table 2, Fig. 2), suggesting hybrid incompatibilities originate on one or both of the sex chromosomes. Second, in some crosses hybrid male sterility was asymmetric and depended on the species origin of the X chromosome.
These observations confirm and extend previous findings, underscoring the central role that the M. musculus X chromosome plays in reproductive isolation.