A Database for Triticeae and Avena
II. 5. Value of crossing-over between linked genes mo5 and
O. T. Tazhin, Biological Faculty, Department of Genetics, Kazakh State
University, Alma-Ata, 480091, U.S.S.R.
The initial mutant (var. Revelatum from Mongolia), which spontaneously
emerged in 1964, and its identical progenies contain four ovaries in each
flower (one ovary is main and the remaining three ovaries have developed
from stamens), as well as two greenish leaflets instead of lodicules. The
multiovary character in the mutant florets is controlled by a recessive
gene mo5 linked with the hull-less seed gene n (Tazhin 1971,
1980). One may observe a series of multiple alleles mol-mo4 accounting
for a great number of ovaries in barley (Moh and Nilan 1953; Kamra 1966)
but a linkage group has not been established for them as yet.
When crossing mutants with hulled seeded barleys, F1 always have normal
hulled seeds and the F2 segregates into normal hulled seed and multiovarian
in the ratio 3:1. In addition, single normal plants with hull-less seeds
Multiovarian plants are homozygous as to their recessive and linked
genes, their genotype being mo5 mo5 nn. In florets of the multiovarian
plants all anthers transformed to ovaries, therefore self-pollination and
fertilization do not occur in them and the hull-less seed gene is not evident.
Hulled seeded barleys to be crossed with the multiovarian mutants are homozygous
for both dominant genes, their genotype being ++/++. Their F1 are heterozygous
for both genes and have the genotype +mo5/+n.
Two types of non-crossover (mo5n and ++) and two types of crossover
(mo5 + and + n) ovicells and spermatozoons are formed with
equal frequency in flowers of F1 plants.
As a result of self-pollination and fertilization of non-crossover ovicells
with non-crossover spermatozoons hulled caryopses form in flowers of F1,
as a consequence non-crossover plants in the ratio 3 normal hulled occur
in F2: 1 multiovarian by phenotype and 1++/++:2+mo5/+n:l
Due to fertilization of crossover gametes with the non-crossover ones
hulled caryopses form in florets of F1, as a consequence crossover plants
in the ratio 4 normal hulled occur in F2 :2 normal hull-less seed: 2 multiovarian
by phenotype and 2+ mo5/++:2++/+n:2+ mo5/nn:
2 mo5mo5/+n by genotype.
Owing to fertilization of crossover gametes of two types hulled caryopses
form in flowers of F1, as a consequence crossover plants in the ratio 2
normal hulled occur in F2 :1 normal hull-less seed: 1 multiovarian by phenotype
and 2+mo5/+n:l++/nn: lmo5mo5/++ by genotype.
Thus in the presence of crossing-over during the formation of female
and male gametes four phenotypic classes arise in F2. However, crossover
hulled plants are phenotypically not distinguishable from the non-crossover
hulled ones and crossover multiovarian plants are phenotypically not distinguishable
from the non-crossover multiovarian plants F2. As a resul F2 phenotypically
segregated into 2 classes of plants (normal hulled and multiovarian), but
only single hull-less seed (crossover) plants with the genotypes +mo5/nn
and ++/nn segregate. Therefore, the crossing-over percentage was
derived only with consideration of one class (i.e. hull-less seed barley)
where p - fraction of crossover plants, n - total number of plants,
c number of hull-less seed plants in F2. The value of crossing-over between
the linked genes mo5 and n in barley thus derived is given
in Table 1.
Table 1. Value of crossing-over (%) between linked
genes mo5 and n in barley as to 10 hybrids F2 multiovarian
x normal hulled (data obtained in 1970-1978).
During 1970-1978 segregation of 1O hybrids (F2 multiovarian x hulled)
has been studied. Normal two-rowed hulled barley var. Nutans was used as
a male parental form. As to the total of combinations, hybrids F2 segregated
into normal hulled and multiovarian in the ratio 3:1. Ten hybrids of F2
taken into account, 61 plants with hull-less seed were established within
9 years. On the linearity test the progeny of each plant out of 61 plants
segregated into normal hull-less seed and multiovarian in the ratio 3:1.
Thus, all hull-less seed plants occurring in F2 were the crossover ones
with the genotype +mo5/nn. The poor infructescense of hybrid
grains on artificial pollination (on the average 3.3%), their low field
germination rate (below 70%) made it impossible to obtain a sufficient
number of plants in F1 and F2 to establish crossover hull-less seed plants
with the genotype ++/nn among F2.
As is seen from Table 1, the value of crossing-over between the genes
mo5 and n as to one class (i.e., hull-less seed barley) varies
from 1-3% depending upon years and crossing combinations. It varies even
within one and the same combination as far as years are concerned. Thus,
as to 3 combinations F2 multiovarian x Nutans 19180 the crossing-over value
varies within 1.6 - 2.5% depending upon years. As to 4 combinations F2
multiovarian x Nutans 187 it varies within 1.0 - 2.62% which probably depends
upon the peculiarities of pollinator varieties and F hybrid growth condition
and development. It is impossible to obtain fuil information on the crossing-over
value estimation considering only the hull-less seed barley. Most valid
data on the value of crossing-over between the genes mo5 and n
were obtained as a result of two combinations of analyzing crossing. In
such case the multiovarian maternal plant forms one type of ovicells (mo5n)
while the heterozygous male parental plant forms as to both genes, i.e.
hybrid F1, forms 4 types of spermatozoons, two of which are the non-crossover
types (mo5n and ++) and the other two are the crossover ones (mo5+
and +n). When artificially pollinated by pollen F1 hybrid grains
(on the average 3.3%) with poor field germination (below 70%) form in flowers
of multiovarian plants, giving rise to non-crossover parental plants in
the progeny, their ratio being 1 normal hulled: 1 multiovarian and that
of the crossover ones being 1 normal hull-less seed: 1 multiovarian. The
crossover multiovarian plants with the genotype mo5 mo5/+n
are phenotypically not distinguishable from the non-crossover multiovarian
ones. Due to this fact the hybrids phenotypically segregate into 2 classes
of plants, i.e. normal hulled and multiovarian in the ratio 1:1 followed
by segregating of normal hull-less seed (crossover) plants with the genotype
+mo5/nn. Data on two combinations of crosses are given in
Table 2. Segregation of hybrids of two combinations
of crosses and fraction of crossover hull-less seed plants with genotype
As to the combination multiovarian x (F1 multiovarian x Nutans 187)
the fraction of crossover hull-less seed plants is 2.01%. As far as the
combination multiovarian x (F1 multiovarian x Nutans 19180) is concerned,
it is 1.80%, the average being (2.01 + 1.80) 2 = 1.90%
It should be noted that the occurrence of multiovarian plants with the
genotype mo5mo5/+n that are not phenotypically established
is equal as compared with the crossover hull-less seed ones in the ratio
1:1. Thus, the fraction of the crossover hull-less seed plants class multiplied
by 2 gives 1.90 x 2 = 3.80%. Consequently, the value of crossing-over between
the linked genes mo5 and n in barley averages 3.8%.
Kamra, P. 1966. Genetic control of the development of floral organs
in Hordeum vulgare. Mechanism of mutation and inducing factors.
Proceedings of Symposium in Prague, August 9-11, 1965, pp. 213-215.
Moh, C. C. and R. A. Nilan. 1953. Multi-ovary in barley. J. Hered. 44:183-184.
Tazhin, 0. T. 1971. Inheritance of the multiovarian characteristic by
barley. In collection "Biological Sciences", Kazakh State University Press,
Alma-Ata, pp. 69-72.
Tazhin, 0. T. 1980. The linkage of the genes mo5 and n
in barley. Barley Genet. Newsl. 10:69-72.
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