Analysis of Genes for Stigma Coloration in Rice - IRRI books

Table 3. Segregation analysis of fragments homologous to B1 and B2 in F 2
population.
Fragment
Size (kb)
P1 a
P2 b
F 2 population
Present
Absent
c 2 (3:1) c
B2
B1
15 Present Absent 103 40
7.1 Absent Present 129 154
2.5 Present Absent 108 35
0.0
16.3**
0.0
a b c Maternal parent Kasalath (indica). Paternal parent F1134 (japonica). **= significant at the 1%
level.
The presence-to-absence ratios of the three fragments were estimated in the F 2
population (Table 3). The observed ratios of 2 fragments, the B2-homologous 15-kb
fragment and the B1-homologous 2.5-kb fragment, were consistent with a 3:1 ratio and
thus showed normal Mendelian inheritance. However, the segregation of the B1-
homologous 7.1-kb fragment deviated from 3:1. The deviation might be explained by
the fact that a gametophyte gene (Nakagahra 1972), which affected pollen fertility, was
linked to the B1-homologous 7.1-kb fragment, because RFLP probes linked to it also
showed deviated segregation (unpubl. data).
All three fragments were null alleles, i.e., present only in either the indica or japonica
parent. Two B1-homologous sequences were revealed to be independent alleles by
segregation analysis, and probably occupy different map positions in indicas and
japonicas.
The origin of the sequences of these plasmid-like DNAs is unknown. If nuclear
sequences homologous to the plasmids were derived from mitochondrial plasmids, our
results might be explained by the fact that transmission event of the plasmids into the
nuclear genome had occurred independently in indicas and japonicas. Alternatively,
sequence transposition could have occurred during the course of rice differentiation
into subspecies. Further mapping of these sequences is currently being done.
References cited
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Nuclear DNAs homologous to mitochondrial plasmid-like DNAs in rice 371