Metaphase I bound arms and crossing over frequency in rye III. Non-chiasmate bonds in desynaptic plants

Abstract

SUMMARYIn order to analyze the correspondence between the number of metaphase I bonds and the chiasma frequency of specific chromosome arms in desynaptic plants, two Fl hybrids were backcrossed to the parental inbred lines. The plants obtained were desynaptic. Some of these plants were heterozygous for a prominent telomeric C-band in chromosomes 1R (long arm) and/or 2R (short arm).From the frequency of bound arms at metaphase I and the frequency of recombined chromosomes at anaphase I in the arms considered, estimates of chiasma frequencies have been derived. The results have been compared with those obtained for the Fls between inbred lines from which the desynaptic plants were produced Orellana and Giraldez, 1981) as well as with those obtained in an open pollinated variety of rye (Orellana and Giraldez, 1981). The excess of anaphase I parental chromosomes found in the desynaptic plants can be explained on the assumption that some of the bonds appearing at metaphase I are achiasmate and a remnant of prophase pairing.

Metaphase I bound arms and crossing over frequency in rye. IV. Triticale-rye hybrids

“…In this case all bonds formed in the short arm of bivalent 1R would be nonchiasmate while in the long arm non-chiasmate bonds would appear with a probability NCB=0215. This value can be compared with the one obtained in an earlier work (Orellana and Giraldez, 1983) for the same chromosome arm in desynaptic plants of rye (B1PEE). In that instance the frequency with which the long arm of bivalent 1R was not bound at metaphase I was NB=0•0225 and the frequency of anaphase I parental chromosomes was Fp = 0'2072.…”

“…The existence of non-chiasmate bonds proposed earlier (Orellana and Giraldez, 1983) in desynaptic rye would easily explain an excess of anaphase I parental chromosomes when compared to the frequency with which a given chromosome arm is not bound at metaphase I. These non-chiasmate bonds would represent a remnant of prophase pairing that could be similar to the process found in achiasmate organisms in which chromosomes remain paired till anaphase I onset (see Baker et a!., 1976).…”

“…From the frequency of being bound at metaphase I and the frequency of recombinant chromosomes at anaphase I or metaphase II in the arms considered, estimates of chiasma frequencies were derived. The materials employed in those instances were an open pollinated variety of rye (Orellana and Giraldez, 1981), the Fl s between rye inbred lines Orellana and Giraldez, 1981) and partially desynaptic plants obtained from the backcrosses between those Fls and their parental inbred lines (Orellana and Giraldez, 1983).…”

Molecular Assembly of Meiotic Proteins Asy1 and Zyp1 and Pairing Promiscuity in Rye (Secale cereale L.) and Its Synaptic Mutant sy10

“…Sticky, nonchiasmate associations may reflect the promiscuity of chromosome configurations at an earlier stage of meiosis. However, since they are largely random, it would appear that they have no functional significance in terms of rescuing achiasmate meiosis, as has been suggested for desynaptic (Orellana and Giraldez 1983) and inbred rye (Cermeno et al 1984).…”