Supplemental mapping of the gene Chi-32 on chromosome 3

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-2^S) was crossed with line Wt8905 (Chi-32 m Lap-2^f) 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-2^f) xWt15327 (chi-32 M Lap-2^S)

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

***P< 0.001

¹Homozygous slow Lap-2^S Lap-2^S.

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

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