Detection of the time of occurrence of nondisjunction induced by the r-X1 deficiency in Zea mays L.

Abstract

The r-X1 deficiency in maize produces high frequencies of aneuploid progeny by inducing nondisjunction during embryo sac development. The purpose of this investigation was to determine the embryo sac division at which the nondisjunctive event takes place. Monosomic-6 individuals were generated by crossing r-X1 containing plants by those carrying the y-pastel-8549 allele of the Y locus on chromosome 6. A strict dosage relationship exists between the number of dominant alleles of the Y locus and the level of β-carotene in the endosperm. We found that the level of β-carotene in the endosperm of kernels containing monosomic-6 embryos was comparable with that found in endosperms with one Y allele. This indicated that they contained only one maternally contributed chromosome 6. Only nondisjunction at the second postmeiotic division could have produced such an endosperm; thus, the nondisjunctive event occurs at this division. Another endosperm type expected from nondisjunction at this same division, with three dominant Y alleles, was not found. The absence of this endosperm type suggests that the egg nucleus and the polar nucleus originating at the micropylar pole are sister nuclei that arose from the same cell at the third embryo sac mitotic division. Key words: aneuploidy, embryo sac, nondisjunction, r-X1 deficiency, Zea.

Cloning of the y1 Locus of Maize, a Gene Involved in the Biosynthesis of Carotenoids.

“…The level of provitamin A activity was found to be directly proportional to the number of Y1 allele copies in the endosperm. This relationship has been confirmed more recently by Simcox et al (1987), who used high-performance liquid chromatography to measure endosperm carotenoid content. Mangelsdorf and Fraps (1931) suggested that the y1 gene product was not an enzyme involved in the biosynthesis of /i-carotene because the rate of an enzymatic reaction, although dependent on concentration, is seldom directly proportional to the concentration of the enzyme.…”

Aneuploids induced by deficiencies of chromosome 9 and analysis of the time of nondisjunction in cotton

“…For this particular feature, the effect of the deficiency of the long arm of 9 in cotton differs from the r-XI deficiency of maize in that the former induces the loss of chromosomes significantly more frequently than the additions of chromosomes. Simcox et al (1987) used an endosperm marker gene to determine the time of chromosome nondisjunction during embryo sac formation and concluded that the r-XI deficiency induces nondisjunction at the second post meiotic division.…”

Jittery, a Mutator Distant Relative with a Paradoxical Mobile Behavior: Excision without Reinsertion

“…However, more than half of them do not breed true, for example, they carry an embryo and an endosperm that are genetically discordant, indicating that the reversion events that produced them occurred postmeiotically (i.e., at one of the megagametophytic mitoses). Conversely, full Bz9 revertant plants are occasionally seen in bz-m039 families planted from spotted seed, providing evidence that bz-m039 can specifically revert in the last gametophytic mitosis that gives rise to the egg and to its sister polar nucleus (Cooper, 1938;Simcox et al, 1987). Nevertheless, concordant germinal Bz9 reversion events occur, mostly as single kernels in the ear, at a frequency of about 1 per 1000 gametes (Table 1).…”