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Mutations of the mouse Attractin (Atrn; formerly mahogany) gene were originally recognized because they suppress Agouti pigment type switching. More recently, effects independent of Agouti have been recognized: mice homozygous for the [Atrn.sup.mg-3J] allele are resistant to diet-induced obesity and also develop abnormal myelination and vacuolation in the central nervous system. To better understand the pathophysiology and relationship of these pleiotropic effects, we further characterized the molecular abnormalities responsible for two additional Atrn alleles, [Atrn.sup.mg] and [Atrn.sup.mg-L], and examined in parallel the phenotypes of homozygous and compound heterozygous animals. We find that the three alleles have similar effects on pigmentation and neurodegeneration, with a relative severity of [Atrn.sup.mg-3J] [is greater than] [Atrn.sup.mg] [is greater than] [Atrn.sup.mg-L], which also corresponds to the effects of the three alleles on levels of normal Atrn mRNA. Animals homozygous for [Atrn.sup.mg-3J] or [Atrn.sup.mg] but not [Atrn.sup.mg-L], show reduced body weight, reduced adiposity, and increased locomotor activity, all in the presence of normal food intake. These results confirm that the mechanism responsible for the neuropathological alteration is a loss--rather than gain--of function, indicate that abnormal body weight in Atrn mutant mice is caused by a central process leading to increased energy expenditure, and demonstrate that pigmentation is more sensitive to levels of Atrn mRNA than are nonpigmentary phenotypes.

The recombination frequency as influenced by five independent recessive ds genes was measured on three segments of different chromosomes of rice, Oryza sativa L. Each ds gene in the homozygous condition resulted in an almost equally reduced recombination frequency in the three segments. When the mean reduction in recombination frequency was related to the reduction of chiasma frequency, the five ds genes were divided into two types: in one type the reduction of chiasma frequency almost corresponded to the mean reduction of recombination frequency, and in the other the chiasma frequency was greatly reduced in comparison with the mean reduction of recombination frequency. Three of the five ds genes were found to belong to the former group. In both types, normal synaptonemal complexes were observed in pachytene cells homozygous for ds genes. This finding suggests that ds genes do not affect the formation of synaptonemal complexes which are regarded as the prerequisite structure for crossing over.