| Popis: |
Our previous data showed that mutation ade13-1, blocking steps 8 and 12 of purine biosynthesis in the yeast Saccharomyces cerevisiae, caused the inability of strains manifesting this activity to grow on the complete nutrient medium with glucose in addition to the loss of adenylosuccinate lyase activity. It was also determined that the ade2-D mutation, inactivating aminoimidasole ribonucleotide carboxylase (the enzyme of step 6), suppressed this phenotypic manifestation of ade13-1; i.e., the ade2-D mutation restores the ability to grow on this medium. When spores of a hybrid that contained both mutations in the heterozygote were germinated on the YEPD medium, almost complete viability of segregants with genotypes ADE2 ADE13 and ade2-D ADE13 and the absence of ADE2 ade13-1 growth were observed. The number of growing segregants ade2-D ade13-1 amounted to approximately half of the possible number. In this work, a decrease in the proportion of segregants with this genotype was shown to occur only when they were obtained as a result of the segregation of hybrids with the normal allele (ADE2) in the heterozygote. The proportion of segregants with genotype ade2-D ade13-1 did not decrease upon segregation of hybrids similar in the genetic background and containing the ade2-D mutation in the homozygote and ade13-1 in the heterozygote. Spores with this genotype formed in the diheterozygous diploid were able to germinate on a medium containing glycerol and to further grow on a medium with glucose. The data suggest that, when a product of the normal ADE2 allele or of another gene, the synthesis of which is stimulated in the presence of this allele, enters spores with genotype ade2-D ade13-1 during meiosis, some of these spores lose their ability to grow on the medium with glucose; i.e., the ADE2 allele can be phenotypically expressed in the spores that did not contain this allele. This phenomenon is similar to the maternal effect known in some species of animals from various systematic groups. |
