Interchange Heterozygotes Research Articles

THE ORIENTATION OF MULTIPLE ASSOCIATIONS RESULTING FROM INTERCHANGE HETEROZYGOSITY

Among the many factors thought to influence the orientation associations in interchange heterozygotes, previous evidence suggests that there is a genetically controlled mechanism (or mechanisms) which is distinct from that varying the position and number of chiasmata. In rye, variation between 50% and 90% disjunction frequency has been ascribed to this mechanism. Nevertheless, in this species, directed segregation has been found in newly arising interchanges, suggesting that the genetic constitution has been selected to give a high disjunction frequency. Two alternative explanations for these findings were considered. First, the influence on orientation may be a secondary effect of factors whose primary effect is of selective importance in normal, non- interchange individuals. Second, direct selection for a high disjunction frequency may have occurred in a manner analogous to Fisher's theory of the evolution of dominance. (auth)

X-ray induced Chromosomal Aberrations in Rice Plants

Dry and soaked seeds of several varieties of rice plants were irradiated with various degrees of doses at 120KVP, 3mA, distance 26cm., no filter. Results of cytogenetical observation of various sterile plants caused by the chromosomal aberrations were briefly summarized as follows:1. About 68 per cent of the chromosomal aberrations observed was the interchange heterozygote including (4) and (4)+(4), and about 32 per cent was trisomics, asynapsis, syncyte formation and polyploidy.2. The interchange heterozygotes were divided into several types based on the frequencies of ring or chain formation of four chromosomes at diakinesis.3. The fertility (seed or pollen) in the interchange heterozygote rans approximately parallel to the frequency of side-by-side configuration of the interchage complex at metaphase-I.4. Fertility in the progeny of the selfed interchange heterozygote differed from plant to plant, that is, some plants divided into two fertility groups, high and low, and other one showed continuous deviations.5. In the progeny of the selfed interchange heterozygote, plants with RT (interchange heterozygote) and without RT (non-interchange heterozygote) showed the segregation of 1:1 ratio.6. In the same interchange heterozygote, there was such a case showing much difference in distribution of fertility and segregation of the interchange heterozygote.7. Asynapsis and syncyte formation were observed. Especially, the latter is the first example in rice plants.8. Polyploidies, such as haploidy, triploidy and tetraploidy, have also been isolated from the progeny of X-ray irradiated rice plants.

Chromosomal status, gene exchange and evolution inDactylis

1. A survey has been made of chromosome numbers in natural populations ofDactylis. Diploids (2n=14), tetraploids (2n=28) and hexaploids (2n=42) have been found in our material, and B-chromosomes have been noted, particularly in diploid plants. In the F.A.O. collections accession numbers are given wherever interesting chromosome numbers have been found. 2. Chromosome pairing has been studied in each of the chromosome number groups, and in diploid x diploid, and tetraploid x tetraploid hybrids. The gross similarity of the chromosome sets inDactylis has been demonstrated. Minor genetic and (or) chromosomal differences have been found between tetraploid populations. 3. Chromosome pairing in the natural hexaploids is regular but variable. 4. Interchange heterozygotes have been observed and analysed in the three chromosome groups. 5. Chromosome breakage and reunion is frequent in plants derived from seed which has lost much of its germination capacity.

STERILITY IN INTERCHANGE HETEROZYGOTES OF BARLEY

Introduction In his paper proposinc the Oenothera method of establishing homoP zygous lines from promismg hybrids, Burnham (1946) suggested that the niethod may be applied to barley xvhere the chromosome number is small (211=14) and where interchange heterozygotes with 3 ring of four chromosomes are not accompanied b y an excessive decrease in fert~li ty. Various degrees of sterility have bcen reported in interchange heterozygotes of barley. These are summarized and prese~lted in Table I . As can be seen in the table, most of these studies dealt with simple interchanges. Relatively little work has bcen reported on the stcrility in plants heterozygous for interchanges at higher levels of chromosoine participation. T h e present study was conducted t o determine the effect of level of chromosonie interchange on sterility. Materials and Methods Thirty-one crosses werc made among 35 homozygous interchange stoclts of barley and 25 crosscs were inade between these stoclts and the normal R4ontcaln1, to produce hybrids heterozygous fo r interchanges of various cornbinations. T h e interchange stoclts wcre from four different sources. All C stoclts and the stoclt 4256-1 were f rom the Department of Agronomy and Plant Genetics, University of R4inncsota, E r t and X T stoclts were from the Swedish Seed Association. Svalijf. and stoclt 7031 was ~ r o d u c e d a t the Department of Field ~ u s b a n ' d r ~ , 1 , i v c r s i t ~ of ~asltatchex\;an. Roman numeral stocla are multiple interchange stoclts developed at the University of AjIanitoba b y crossing simple interchange stoclts. T h e designation of each stoclt and the interchanee cl~romosoiiies involved can bc found in Tablc 11. 0 Pollen niother cells f rom I;, plants were exalllined cytologically to confirm the presence of expected metapliase configurations. Sced set was determined fo r each I;, plant. Per cent sterility was calculated b y number of sterile s~il telets

Seperation of Trisomic and Diploid Barley Seeds Produced by Interchange Heterozygotes1

SynopsisA seed blower can be used to obtain seed lots that contain a high frequency of trisomics since most of these are found in the lighter seed.

Trisomics from Interchange Heterozygotes in Barley1

Trisomics from Interchange Heterozygotes in Barley¹

X-ray Induced Chromosomal Aberrations in <i>Hordeum</i>

X-ray treatment was applied to dormant seeds of Hordeum spontaneum C. Koch var. transcaspicum Vav. by Matsuda's Type KXC-17 apparatus at 180kVp, 3mA, no filter. The dose was about 13, 500r units. Seventy eight plants in X2 generation which were raised from semi-fertile (fertility less than 50%) X1 plants were cytologically investigated. The results are summarized as follows:1. Chromosome interchanges were observed in 13 plants from 9 head progenies. One ring of eight, 2 ring of four, and one ring of four were observed in 1, 2, and 9 diploid plants, respectively (Tab. 1).2. One of two trisomic plants showed the chromosome associations of 1V+5II and 1III+6II at diakinesis and MI, indicating the tertiary nature of the trisomics (Tab. 2).3. Nucleolus-chromosome relationships were determined in all plants with reciprocal translocations (Tab. 2). The ring of eight (Figs. 4a, b), one of the two rings of four in one of the 2 (4)+(4)-plants and the ring of four in 4 (4)-plants (Figs. 1, 2) were attached to the nucleolus, which showed that a member of the interchange was the nucleolus chromosome (chromosome 6 or g-chromosome).4. In one plant a complete failure of pairing was observed, almost all of the chromosomes being univalents at diakinesis and MI. The meiotic process was very irregular followed by complete sterility on both female and male sides.5. The results of Burnham and Hagberg (1956) indicating that the breakage frequency of a certain chromosome varies according to the variety are confirmed.6. The occurrence of trisomic plants in the progeny of interchange heterozygotes is mentioned.

Genotypic control of chromosome behaviour in rye. II. Disjunction at meiosis in interchange heterozygotes

Genotypic control of chromosome behaviour in rye. II. Disjunction at meiosis in interchange heterozygotes

AN INTERPRETATION OF THE OBSERVED AMOUNT OF RECOMBINATION IN INTERCHANGE HETEROZYGOTES OF BARLEY

AN INTERPRETATION OF THE OBSERVED AMOUNT OF RECOMBINATION IN INTERCHANGE HETEROZYGOTES OF BARLEY

Chromosome Breakage and Sterility in the Mouse

SHELL2 has shown that the offspring of X–rayed male mice produced before the onset of complete X–ray sterility contain a certain proportion—depending on the dosage—of semi–sterile individuals, which when outcrossed to unrelated animals throw litters of reduced size. This semi–sterility could be shown to be inherited and was assumed to be due to an interchange of segments between non–homologous chromosomes induced by irradiation. The genetical behaviour of semi–sterility was extensively studied in breeding experiments2,3,1. A great number of valuable data on zygotic lethality during the early embryonic development was also collected by various investigators4,5,6,10, yet so far no cytological analysis of chromosome behaviour in interchange heterozygotes has been attempted. With this programme in view, three semi–sterile lines, A, B and T, each from a differently treated male, were produced by us using the X–ray technique of Snell.

Tetraploid PMCs of Rhoeo induced by low temperature treatment

In the winter of 1937, pots of Rhoeo discolor Hance were transfered from the green house (23°C) to the place of 2°C for four hours and then were put back again. Two weeks after treatment, some anthers were found to contain a considerable number of tetraploid PMCs mixed among the normal diploid ones. The chromosome configurations were studied by one 'diakinesis' (Fig. 6) and nine MI (Figs. 2-4 and 7-15) PMCs. They involved univalents, ring bivalents, chains of three or more chromosomes, rings of 4 chromosomes and polyvalents bearing triple terminal chiasmata. They are all similar to those demonstrated by Seitz (1935) in tetraploid Oenothera species. These 4x-PMCs are ascribed to be due to the failure of cytokinesis at the last mitosis in the archesporial tissues which were affected by influence of low temperature treatments. The chromosome configurations observed favor the assumption that Rhoeo is an interchange heterozygote as has been hitherto inferred only from ring configurations.

Trisomics inPisum sativum derived from an interchange heterozygote

InPisum sativum tertiary trisomics and trisomic interchange heterozygotes have been derived from Hammarlund’sK-line interchange heterozygote, which has a meiotic association of four chromosomes. The origin of the trisomics is shown to be in numerical non-disjunction of the association of four in one only of the four possible ways.

The limitation of crossing-over inOenothera

The simplest method of origin of ring formation, direct segmental interchange, gives interchange heterozygotes which inevitably contain segments of chromosomes of three different types in respect of crossing-over;differential segments with no crossing-over,interstitial segments (proximal to the interchange) with reduced and deleterious crossing-over, andterminal segments with simple crossing-over. These different kinds of segments account for the existence of a complex, of genes characteristically associated with the complex, and of others in which freer crossing-over is possible and no characteristic association with the complex occurs.

The Behavior of Interchange Heterozygotes in Oenothera

In a recent number of these PROCEEDINGS, Emerson' suggests that certain breeding results are incompatible with my view of the genetic structure of complex in Oenothera.2 He points out, first, that crossing-over between genes is as great in the multiple rings as in the simple ring pairs and, secondly, that this crossing-over is not accompanied by interchange of non-homologous segments and consequent change of configuration in the progeny.* My view, however, is that, while certain genes, which are sometimes associated with complexes, cross over freely without interchange, the essential and permanent differences between complexes must depend upon genes which are normally incapable of crossing-over, owing to their being differently arranged in the chromosomes following structural change, and owing to their being situated next to the spindle attachment. Thus Emerson believes that the differences between complexes can be resolved into differences between independently segregating genes while I believe that they are inherently incapable of such resolution because they are associated with structural changes such as translocation, deficiency and reduplication. Since I put forward this suggestion new'evidence bearing on the question has appeared, particularly from observation of interchange heterozygotes in maize4 and Pisum.5 In these it is found that interchange has occurred in the arms of the chromosomes at some distance from the spindle attachment. It follows in such cases, as E. R. Sansome has pointed out, that a ring of six can (and indeed must) arise from two interchanges in such a way as to give interstitial homologous X-segments in two chromosomes both of whose ends are non-homologous. This statement may be generalized as follows: Every successive interchange by which a ring of four is increased to six, eight and so on, will give one such new relatively translocated segment in opposite complexes unless two interchanges coincide. Thus, consider a ring of four and one pair of the following segmental constitution: