Pisum Genetics 

Volume 23

1991

Research Reports

pages 14-15

Supplemental mapping of the gene Chi-32 on chromosome 3

Czerwinska, St.,

and B. Wolko

 Plant Experiment Station, Wiatrowo

62100 Wagrowiec, Poland

The chlorotica mutant chi-32 was induced in the line Wt3519 by using fast neutrons for the radiation treatment of dry seeds. The F9 generation analysis of the two point cross Wt11288 (testerline) x WT15325 (mutant) showed linkage between chi-32 and gene M in chromosome 3 (CrO% = 8.5 1.7) (1). A recombinant line with genotype chi-32 M was selected from fhis test and included in our Pisum gene bank as the line Wt15327.

We chose a second marker, the gene Lap-2, for mapping of the chi-32 locus. According to Weeden and Marx (2) the recombination fraction for M - Lap-2 equals 9.0 4.9. Line Wt15327 (chi-32 M Lap-2S) was crossed with line Wt8905 (Chi-32 m Lap-2f) and single locus segregation data are shown in Table 1 A. All polymorphisms displayed segregation ratios close to those expected for single gene traits. Joint segregation analysis of chi-32 and markers on chromosome 3 revealed a non random assortment with M (CrO% = 13.7 7.1) and with Lap-2 (CrO% = 10.2 2.3). The recombination fraction for the pair M - Lap-2 was 18.8 7.0 (Table 1 B) This three-point linkage analysis on chromosome 3 indicates the following ranking of the loci:

Our results indicate that the gene Chi-32, which controls a chlorophyll mutation, is placed between M and Lap-2 on chromosome 3. Previous results of Weeden and Marx (2) reveal a smaller distance between M and Lap-2. The cause of this inconsistency is not presently known.

Table 1. Phenotypic distribution in an F2 population derived from cross Wt8905
(Chi-32 m Lap-2f) xWt15327 (chi-32 M Lap-2S)

A. Monohybrid segregation

Locus

X

x

Total

Chi-square (3:1)

Chi-32

144

49

193

0.01

M

136

51

187

0.51

Lap-2

140

511

191

0.29

B. Joint segregation of chlorotica chi-32 with M and Lap-2:

Gene pair

XY

Xy

xY

xy

Total

Joint
Chi-sq.

Rec. fract.

S.E.

Chi-32 : M

91

51

45

1

187

19.77***

13.74

7.14

Chi-32 : Lap-2

132

111

8

401

191

105.06***

10.23

2.33

M : Lap-2

88

461

49

21

185

17.77***

18.88

7.03

***P< 0.001

1Homozygous slow Lap-2S Lap-2S.

  1. Czerwinska, St. 1988. PNL 20:9-10.

  2. Weeden, N.F. and Marx, G.A. 1984. J. Heredity 75:365-370.