4. Comparison of length between chromosomes 2 and 3

H. I. OKA

National Institute of Genetics, Mishima, 411 Japan

There is a descrepancy between chromosomes 2 and 3 designated by different authors, as Oka and Wu (1988) has pointed out. The two chromosomes show a difference in arm ratio, which may be used for their distinction. As shown in Table 1, data A, B, C and F (group 1), chromosome 2 has greater arm ratio than chromosome 3, and vice versa in data D, E, G and H. In this note, the numbering by the authors of group I is adopted.

The 8 sets of data for relative length of the two chromosomes are summarized

Table 1. Arm ratios of chromosomes numbered 2 and 3 by different
         authors
________________________________________________________________
Author (I)           Chromosome   Author (II)        Chromosome
                     2      3                        2      3
________________________________________________________________
A.Shastry et al.1960 2.17 1.23  D.Chung&Wu 1987     1.17  1.93
B.Kurata et al. 1981 1.69 1.18  E.Chen et al.1982   1.16  1.89
C.Kurata's report^a 1.58 1.13  G.Chung&Wu 1987     1.28  1.88
F.Kurata&Omura 1978  1.67 1.37  H.Fukui et al.1988  1.25  1.60
________________________________________________________________
A,B,C,D and E-Pachytene   F, G and H-Somatic prometaphase
a: A report by Dr. N. Kurata submitted to IRRI in 1986.

Table 2.  Comparison of relative length between chromosomes 2 
          and 3 as designated by authors A, B, C and F
________________________________________________________________
                    No. of Relative length (%) Difference
Author    Stage            ___________________
                    cells  Chr. 2   Chr. 3      (2)-(3)     t
________________________________________________________________
A.Shastry 
et al.    Pachytene   10   11.88    11.75        0.13     Unable
      (1960)                                             to test

B. Kurata 
et al.      "          4  12.0+-0.8 12.0+-1.7    0.0        0
  (1981)

C. Kurata's 
report      "       6,5 11.68+-0.15 11.60+-0.46  0.12   0.37^ns  
   (1986)

D.Chung&Wu  "        25 10.82+-0.78 12.15+-0.74 -1.33  6.22**
   (1987)

E.Chen 
et al.      "        25 1O.95+-1.10 12.47+-1.10 -1.52  4.89**
  (1982)

F.Kurata&
Omura   Prometaphase 10 12.2        11.2         1.0   Unable
(1978)                                                to test

G.Chung&Wu '         35 11.12+-0.75 11.70+-0.63 -0.58  3.54**
   (1987)

H. Fukui 
et al.               10 10.08+-0.84 11.20+-0.95 -1.12  2.79*
 (1988)
 
Mean (from
ANOVA;LSD               11.00       11.95
1%=0.34    Pooled  107      (alpha dif=0.133)  -0.95  7.14**
_______________________________________________________________
*P<0.05; **P<0.01, ns: Non-significant.

in Table 2. In data A, C and F, chromosome 2 is longer than chromosome 3, but the differences are either unable to test (standard deviations are not given) or insignificant. No difference in length is reported in data B. In other four sets of data (D, E, G and H), chromosome 2 is shorter than chromosome 3 significantly. Data H obtained by computer-aided image analysis may be considered most reliable.

The whole data were subjected to analysis of variance, taking those not giving standard deviations as single determination. There was a small unequality in sample size as 6 measurements for chromosome 2 and 5 for chromosome 3 were recorded in data C, but this seemed to little affect the authogonality of comparisons. The F test proved that the difference in relative length between the two chromosomes was highly significant (Table 3). Unexpectedly, the author X chromosome interaction was not significant. The t test with the pooled data derived from the analysis of variance also showed that when the numbering by author-group I was adopted, chromosome 2 was significantly shorter than chromosome 3. If the numbering by author-group II is adopted, chromosome 2 is longer than chromosome 3. Accordingly, chromosomes 2 and 3 by author-group I have to be renumbered 3 and 2, respectively.

Table 3. Analysis of variance of relative length data for
             chromosomes 2 and 3
________________________________________________________________
Source of variation                df      Mean square  F
________________________________________________________________
Chromosome (2:3)                    1         48.455  59.4**
Stage (pachytene: prometaphase)     1          8.574  10.5**
Chromosome X stage                  1          3.223   3.95*
Author                              6          2.116   2.60
Authorxchromosome                   6          2.064   2.53
Error (single measurements)       197          0.815
________________________________________________________________
* P<0.05; ** P<O.O1

References

Chen, J. T., H. C. Lai, Y. H. Hwang, M. C. Chung and H. K. Wu, 1982. Identification of rice reciprocal translocation and the location of lazy gene. Bot. Bull. Acad. Sinica 23: 71-87. (Chinese/English)

Chung, M. C. and H. K. Wu, 1987. Karyotype analysis of IR36 and two trisomic lines of rice. Bot. Bull. Acad. Sinica 28: 289-304. (Chinese/English)

Fukui, K., K. Kakeda, K. Iijima and K. Ishiki, 1988. Computer-aided identification of rice chromosomes. RGN 5: 31-34.

Kurata, N. and T. Omura, 1978. Karyotype analysis in rice, 1. A new method for identifying all chromosome pairs. Jpn. J. Genet. 53: 251-255.

____, ____ and N. Iwata, 1981. Studies on centromere, chromomere and nucleolus in pachytene nuclei of rice, Oryza sativa, microsporocytes. Cytologia 46: 791-800.

Oka, H. I. and H. K. Wu, 1988. Comparison of data on rice chromosomes presented by different authors. RGN 5: 34-41.

Shastry, S. V. S., D. R. Ranga Rao and R. N. Misra, 1960. Pachytene analysis in Oryza, I. Chromosome morphology in Oryza sativa. Ind. J. Genet. Plant Breed. 20: 15-21.