The Remarkable Low Ratios of Recessive Segregates in Oryza sativa

Abstract

1. The dwarf mutant is characterized by its stunted growth and deep green foliage. The form bears highly sterile ears, only 0.7 percent of spiklets being fertile when the ears were bagged.
2. Although the dwarf sterile form is monogenically recessive to normal, the segregates exhibit a remarkable low ratio. By pedigree culture or through crossing, the average 4.0 percent of the dwarf segregates is virtually constant through generations. Compared with the homozygous, only slightly more heterozygous pedigrees are produced.
3. The rmarkable deficit is regarded as being due to the certation between the normal and dwarf microgametophytes in the course of fertilization. The chances of fertilization are calculated to be 11.5 normal: 1 dwarf in gametic proportion.
4. The slender mutant seedlings are very elongated and the leaves yellowish green. The form, which is non-viable, die about two months after germination.
5. The slender segregates showed a very low ratio in the first two generations (3.0 percent and 3.1 percent respectively), while the number of heterozygous pedigrees was very small. In the third year, the ratio of the slender increases to an average of 14.8 percent, although it varied in a remarkably way. An increase was witnessed also in the proportion of the hetorozygous pedigrees.
6. The deficit in the slender segregates is believed to be caused by the disharmony of the slender gene with respect to the plasm. The adaptation of the plasm in later generations, by lessening the disharmony, results in the segregation approaching the monohybrid. The slender mutation therefore is due to a monogenic recessive.