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Wheat Information
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Number 72: 60-63 (1991)
III
Records
Proceedings of the 22th Wheat Genetics Symposium of Japan
The 22th wheat Genetics Symposium of Japan was held on December
15 and 16,1990 at Nara, Japan, chaired by Dr. T. R. Endo. The
followings are the proceedings of the presentations. Addition to the
reports on wheat studies, Dr. M. Hori and Dr. H. Ogura presented
recent topics of human genetics and rice breeding, respectively.
Chromosome mapping by use of aneuploids in wheat
Kozo Nishikawa
Faculty of Agriculture, Gifu University, 1-1 Yanagido, Gifu-shi
501-11, Japan
The term, chromosome map includes genetic map and cytological or
cytogenetical map. Cytological mapping which is referred to as
physical mapping in the broad sense is the subject of the Dr. Y.
Mukai, the second speaker in this symposium. Dr. K. Tsunewaki, the
third speaker will talk about RFLP mapping. So I will confine myself
to the method of genetic mapping of morphological and isozyme markers
by use of aneuploids and discussion of some problems accompanied.
McIntosh (1987) described principle and method for gene location and
gene mapping in hexaploid wheat. McIntosh and Cusick (1987) presented
linkage map of hexaploid wheat. Nomenclature for description of wheat
aneuploids was presented by Kimber and Sears (1968). With the rather
few good markers available, genetic mapping in wheat has not been
well developed. So some data reported in barley and cotton will be
cited for supplement.
1. Hyperaneuploids
a) Trisomic: Primary trisomic had been used to determine the
gene-chromosome association. Trisomic analysis is generally less
efficient than monosomic analysis, and largely applied to diploid
plants, which is hard to withstand hypoaneuploidy. Determination of
genotypes of F2 plants with dominant character makes it
possible to estimate the recombination value, but this is not
realistic, because of too much time and labor to be required.
b) Monotelotrisomic (telotrisomic): Instead of primary trisomic,
monotelotrisomic has been used for determining the centromere
position in diploid plants such as barley. In Fig.1,
the locus A nearby and the locus B far from the centromere on the arm
homologous to telocentric would show chromosome segregation and
random chromatid segregation depending on respective distance from
the centromere, while the locus C on the opposite arm would show
disomic segregation. Thus by monotelotrisomic analysis, centromere
can be positioned between markers when a considerable number of
markers have been mapped on a give chromosome. This had been done by
Tsuchiya and his coworkers in barley (Tsuchiya and Singh 1982).
Similarly, monoacrotrisomic (acrotrisomic) analysis can provide
information on the position of break point of the chromosome
concerned (Tsuchiya et al. 1984).
c) Monoisodisomic: Monoisodisomic carries three doses of loci
locating on the isosome. In cotton recombination value of 16.2%
between centromere and a marker, M1 was obtained in
monotelodisomic for chromosome 4S, while the value of 21.7% in
monoisodisomic 4S (Endrizzi and Bray 1980). The significantly higher
value in monoisodisomic was attributed to chiasma between two isoarms
followed by a chiasma formation between a complete chromosome and one
arm of isosome at the proximal region.
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