Persson (1969 a & b) used T4-6's in linkage studies. Most of the breakpoints which he proposed were based on linkage of erectoides mutants with K (hooded). There are also others, who have done linkage studies with T4-6's. These are cited later in this publication.
The literature for the determination of translocation breakpoints was reviewed in the previous papers in this series (Hagberg et al. 1975, 1978). It is hoped through the publication of this series that the translocations especially those covered in these studies would be more usable to those who are involved in cytogenetic studies.
Material and methods
Twenty-one stocks of 4-6 translocations were used in this study. Diallel crosses between these stocks were performed. Sporocytes from the F/1/-plants were collected in 3:1 solution of alcohol and acetic acid. The sporocytes were stained with orcein and the diakinesis or metaphase I chromosome configurations were studied. These were divided into two groups. Crosses within each group gave 7II but crosses between groups gave 1 IV + 5II.
Pollen from the F/1/-plants of diallel crosses was collected and stained, and the percentage of stained pollen observed.
Some of the 4-6 translocations were crossed onto male steriles. The male steriles in this case were used as an easy method of crossing and producing translocation heterozygotes. This material was also used for linkage studies between the male sterile gene and translocations.
The technique of Tuleen (1971) was followed for fixation and staining of root tips of translocation heterozygotes and homozygotes. In most cases, drawings of chromosomes as well as comparisons were made in order to see if there were any notable differences between the translocated and the normal chromosomes.
When a set of data agreed (diakinesis or metaphase I configuration, stainable pollen, karyotype and sometimes linkage data) the breakpoints were assigned to the long or short arm of the chromosomes involved in the translocation.
Some of the diallel combinations, showing 7II and high pollen fertility in the F/1/, were screened for chromosome segment duplication genotypes in the F/2/ generation, using chromosome arm length variation as selection criteria. The method was described in detail by Hagberg and Hagberg (1978).
Results and discussion
Table 1 also show those crosses between different T4-6's, which gave 7II. The table also gives the amount of stainable pollen. The 7II occur when either the breakpoints are in the same arms of both chromosomes or the breakpoints are in opposite arms of both chromosomes. The latter usually has a smaller amount of stainable pollen probably due to the fact that these paired chromosomes have different chromosome centromeres and do not always give a full genome after meiosis, which causes the formation of non-functional pollen. T4-6o did not fit the pattern but gave a chain of IV in all combinations.
A number of considerations about the relative length of chromosome arms makes this a useful criterion in determining breakpoint positions. Accordingly, when the involved chromosomes in a translocation have one chromosome arm shorter than any normal chromosome arm the translocation breakpoint is in that arm. This is also true when the arm of a translocation chromosome is longer than any of the arms of the normal chromosomes involved in the translocation. In the case of chromosome 6, if the satellite is longer or shorter than normal - the breakpoints occur in the satellite. If the breakpoint is in the nucleolar organizing region the results should be as though the breakpoint had occurred in the short arm. If the breakpoint is at the centromere, one could have more than one combination (Hagberg et al. 1975, Fig. 6).
Table 2 and Figure 1 give the various proposed breakpoints for the T4-6's studied. In five translocations, the breakpoints were in the short arm of chromosome 4 and in the short arm or satellite of chromosome 6; in six translocations in the short arm of chromosome 4 and in the long arm of chromosome 6; in three translocations in the long arm of chromosome 4 and in the short arm of 6; in seven translocations in the long arm
Table 1. Configuration in meiosis (MI) of the F/1/ combination of diallel
crosses between reciprocal translocations involving chromosome 4 and 6, and the
percentage of stainable pollen.
The F1-combinations within the box have 1 IV + 5II, all others 7II.
T4-6o gave chains of IV in all combinations.
_____________________________________________________________________
T4-6 T4-6
_______________________________________________________________
j u s q n m l h g e d o v t r p f c a k i
_____________________________________________________________________
i 92 x) | 66 66
k 90 95 | 73 65
a 92 78 82 88 83 92 88 x) 87|75 z) 57 99 z) 60
c 81 87 85 85 85 84 89 92 73| 45 73 67 z)
f 93 92 92 90 93 82 87 87 78 82 95|52 49 z) 47
p 90 62 95 88 x) 90 88 95 84 90 93 85|77 77 88
r 95 83 91 93 88 87 89 86 91 81|81 54
t 88 x) 86 87 93 90 86 89 87 90|66
v 88 96 89 88 87 93 81 87 83 80 |
o chain: 68 70 77 69 69 63 72 74 72 |
__________________________________________|
d 55 z) 56 68 62 54 56 64 81
e 55 80 z) 60 85 83 86 53
g 55 64 70 56 56 68
h 60 52 59 54 55 55
l 82 47 55 51 71
m 69 59 65 55
n 59 90 73
q 48 54 71
s 51
u
x= IV (pollen fertility not calculated)
z=II (pollen fertility not calculated)
Table 2. Proposed break positions for T4-6's
____________________________________________________________
Designation Chromosome Mode of
recommended previous 4 6 Variety origin
____________________________________________________________
T4-6a rkT2 S L Bonus Chronic r-ray
T4-6c CT 2 L S Bonus Etoxycaffeine
T4-6d DT12 S S Bonus Neutrons
(NTE-12) ert-a23
T4-6e T161 L L Bonus Neutrons
T4-6f T223 L S Bonus Neutrons
T4-6g T267 S S Bonus r-rays
T4-6h T279 L L Bonus r-rays
T4-6i KM21/a/ S L Kanto x-rays
Bansei Gall
T4-6j 584/66 L L Donaria x-rays
T4-6k 382/70 S L Inis x-rays
T4-6l T332 L L Bonus Acute r-rays
T4-6m T356 L L Bonus Acute r-rays
T4-6n T358 S S Bonus Acute r-rays
T4-6o T337 L L Bonus Acute r-rays
chain
T4-6p T381 S L Bonus Acute r-rays
T4-6q T400 S S Bonus Chronic r-rays
T4-6r T439 L S Bonus Acute r-rays
T4-6s T455 S S Bonus Acute r-rays
T4-6t T505 S L Bonus Acute r-rays
T4-6u T551 L L Foma Acute r-rays
T4-6v T555 S L Foma Acute r-rays
L______________________________C______________________________S
e f n a
c u s i
l r q k
m g p
j d t
j v
o 4.
L______________________________C___________________NO_________S
a e f n
i u s
k l c q
p m r g
t j d
v j
o 6.
There was one translocation which did not fit the diallel scheme. This was T4-6o which gave a chain of IV in all combinations. It has one breakpoint in the long arm of chromosome 6, like the T6-7's which do not fit into their diallel scheme. Suggestions as to the cause to this phenomena have been presented by Hagberg et al. (1975, 1978).
Some of the linkage data with T4-6's is presented in Table 3. Most of the chromosome 6 data agree with proposed breakpoints. However, there were many discrepancies in the chromosome 4 data. The placement of T4-6 breakpoints by Persson (1969) and Søgaard (1971) does not agree with cytological data and breakpoints proposed by the authors. Persson (1969 b) has based his proposed breakpoints on the linkage studies between ert-i and K, and the subsequent crosses of T4-6's with ert-i and other marker genes. If this data holds true, then the authors believe that the linkage map of chromosome 4 was reversed. This has also been considered a possibility by Tsuchiya (1973). Later, Singh and Tsuchiya (1974) had obtained trisomic ratio between K and telo 4S. It was not clear to the authors if telo 4S was identified by cytology or because a trisomic ratio was obtained with K. This was questioned by Lehmann et al. (1976). Tsuchiya (1981) found that previously reported telo 4S was in fact telo 4L and therefore reversed the long arm - short arm relationship for chromosome 4, which agrees with the authors data.
In the F2-generation of 3 combinations between T4-6 lines showing 7II in F1, duplication plants, combining the longest 4-6 translocation chromosome from each of two different translocation events, were identified by root tip mitosis.
Translocations have been used to locate genes, produce trisomics and duplications, increase linkage between genes and other beneficial aspects of plant breeding and cytogenetics. The proposal of breakpoints has made it easier to choose which particular translocation to work with. The program to identify translocation breakpoints should be continued in order to reduce the amount of work necessary today for the plant breeders and/or cytogeneticists to select the best translocation for their particular research.
This paper has been cited, but never before published. The paper was originally written at the time when there was much discussion about linkages on the short and long arm of chromosome 4. This was resolved by Tsuchiya (1981).
Table 3. Linkage studies between genes and T4-6's
References
Hagberg, A., G. Persson and G. Hagberg. 1972. Utilization of induced chromosomal aberrations. Translocations, duplications and trisomics in barley. Induced Mutations and Plant Improvement IAEA, Vienna p. 173-182.
Hagberg, A., L. Lehmann and P Hagberg. 1978. Segmental interchanges in barley. II. Translocations involving chromosome 6 and 7. Z. Pflanzenzüchtung 81:89-110.
Hagberg, G., L. Lehmann and P. Hagberg. 1975. Segmental interchanges in barley I. Translocations involving chromosome 5 and 6. Hereditas 80:73-82.
Hagberg, P. and A. Hagberg. 1978. Segmental interchanges in barley III. Translocations involving chromosomes 6 and 7 used in production of duplications. Z. Pflanzenzüchtung 81:89-110.
Hockett, E.A. and R.J. Eslick. 1971. Genetic male-sterile genes useful in hybrid barley production. Barley genetics II:298-307.
Lehmann, L., P. Hagberg and G. Hagberg. 1976. Translocation linkage studies and translocation breakpoints. Barley Genetic Newsletter 6:45.
Persson, G. 1969a. An attempt to find suitable genetic markers for dense ear loci in barley I. Hereditas 62: 25-96.
Persson, G. 1969b. An attempt to find suitable genetic markers for dense ear lock in barley II. Hereditas 63:1-28.
Singh, R.J. and T. Tsuchiya (1974). Further information on telotrisomic analysis in barley. Barley Genetics Newsletter 4:66-69.
Søgaard, B. 1971. Linkage studies on eceriferum mutants in barley. Barley Genetics Newsletter 1:41-47.
Tsuchiya, T. 1973. New linkage maps of barley. Barley Genetics Newsletter 3:99-103.
Tsuchiya, T. 1981. Revised linkage maps of barley, 1981. Barley Genetics Newsletter 11:96-98.