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Frequency of translocations in each population is summarized in
Table2. The frequency varied greatly among
populations from 0.00 in Qazrin to 0.583 in Mt. Hermon. Overall major
translocation frequency in Israel was 0.202. This value agrees quite
well to that reported by Kawahara (1987) but is much lower than the
value of 0.70 obtained by Joppa@et al. (1995), where the threshold
for translocation was 0.04. In order to clarify the cause of this
difference, data of seven common populations of the two reports are
compared as shown in Table 3. Joppa et al.
(1995) considered that quadrivalent frequencies greater than 0.04
represent translocation heterozygotes. According to our present
criteria (more than 0.50), translocation et al. (1995), where the
threshold for translocation was 0.04. In order to clarify the cause
of this difference, data of seven common populations of the two
reports are compared as shown in Table 3. Joppa et al. (1995)
considered that quadrivalent frequencies greater than 0.04 represent
translocation heterozygotes. According to our present criteria (more
than 0.50), translocation frequency became lower in all the
populations and became 0.00 in two population, Qazrin and Yehudiya.
Overall frequency in seven populations listed in Table 3 is 0.260 in
the materials studied by Joppa et al, (1995) and 0.187 in our
samples. The two values did not differ greatly and thus are
considered to represent frequency of 'major' translocation in natural
populations of T. dicoccooides.
Another factor which affects overall frequency is that the two
reports observed different populations in some cases. Some of the
populations studied by Joppa et al. (1995) are homogeneous for one or
more translocations. For example, all 10 genotypes from Beit Oren had
two translocations with very high frequency of quadrivalents, from
0.95 to 1.00. But we could not find populations that are homozygous
for one or more translocations. Such a population would increase
overall frequency even when it is homogeneous. We conclude that there
are two major causes for the difference in estimation of overall
translocation frequency of T. dicoccoides in Israel. One is
the difference in the sampling of population and the other is the
criterion of presence of translocation. In the present report, we
regarded that a genotype is homozygous for a 'major' translocation
when hybrids with testers formed a quadrivalent at a frequency more
than 0.50. Therefore, 'minor' translocation with very short
interchanged segment is not counted here. Apparently, the frequency
of quadrivalents will be very low in hybrids heterozygous for minor
translocation. More extensive and detailed studies are needed to
determine the frequency of translocation in natural populations.
Reference
Kawahara T (1987) Identification of reciprocal translocation
chromosome types in the emmer wheats. III. Six chromosome types in
Triticum dicoccoides. Jpn J Genet 62: 197-204.
Kawahara T (1988) Confirmation of primitive chromosome structure in
the hexaploid wheats. Theor AppI Genet 75: 717-719.
Joppa LR, Nevo E and Beiles E (1995) Chromosome translocations in
wild populations of tetraploid wheat in Israel and Turkey. Theor AppI
Genet 91: 713-719.
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