SUPPLEMENTAL LINKAGE DATA FOR CHROMOSOMES 1 AND 5

PNL Volume 16 1984 RESEARCH REPORTS

Marx, G. A. NYS Agricultural Experiment Station, Geneva, NY USA

Creep-Ce-Fs

In 1982 (5) I reported evidence showing that creep is situated on

chromosome 5. With respect to other markers on that chromosome, the

following order was suggested: Cr-Creep-Fs-Ce. A line homozygous reces-

sive for creep ce fs was recovered from the above study and was used in

the three-point test reported here (Table 1.) The present data confirm

the previous findings in all essential respects except that the inten-

sity of linkage among creep, ce and fs is stronger in this study and

that the order apparently is creep-ce-fs rather than creep-fs-ce. The

order indicated by the present data conforms with the order given in

Lamprecht's 1968 map [see (1)].

The data are divided into two separate analyses because the overall

experiment was conducted in part in the glasshouse and in part in the

field. There was some question about the genotype of 18 F2 segregants,

so these plants were progeny tested to verify their genotype. There

were only two Ce fs crossover F2 plants in the combined populations

comprising 507 plants.

50 PNL Volume 16 1984

RESEARCH REPORTS

Cov Fs

Evidence adduced previously has indicated that cov, a chlorophyll

gene which confers a distinct blue-green foliage color (but without

affecting pod color), is located on chromosome 5 in the vicinity of cr

and gp (3,4). These results lead to the expectation, demonstrated

herein, that cov should show evidence of linkage with fs (Table 2).

Table 2. Analysis of the F2 of a repulsion phase cross Cov fs x cov Fs.

A-Af-I-Am-1

Preliminary data on a cross involving three genes on chromosome 1 ,

af-i-am-1, was reported last year (6). Larger populations of the same

cross were grown and evaluated in the field in 1983. In this case,

however, the seeds from the F1 plants (i.e. F2 seeds) were sorted prior

to planting for yellow (I) and green (i) cotyledon color. Because, as

the analysis of the glasshouse populations demonstrated, the three genes

are rather tightly linked, the I seeds, except for a few crossovers,

were expected to produce plants with normal (Af/-) foliage but

to segregate for A-a, for I-i, and for Am-l-am-1. The am-l/am-1 plants

were expected to be I/I but only the A plants of this group are expected

to show the seed disorder (sd-1) associated with am-1 (that is, sd-2

expression is blocked in the presence of a/a). The second group of

seeds, the ii seeds, were expected to produce (except for crossovers)

afila (af) plants segregating for A-a but not for am-1 and its as-

sociated seed disorder. These expectations were fulfilled in the field

populations (Tables 3 and 4), the only exceptions arising from crossover

events.

PNL Volume L6 1984

RESEARCH REPORTS

Although the cross represents a four-point linkage test, the data

are presented as combinations of specific gene pairs. In view of the

complexity that is introduced by various forms of epistasis it is easier to

comprehend the relationships among all the genes by considering them in

pairs.

Wild-type vs white flower color: The two parents in the cross were

white flowered, one because of a and the other because of am-1. The F1

plants bore wild-type flowers and the overall F2 population satisfactorily

fit a 9:7 for colored vs white flowers, the white flowered class being

composed of a/a and am-l/am-1 plants (Table 3).

Norma1 (Af) vs afila (af) habit and yellow (I) vs green (i)

cotyledons : Since i is linked in coupling phase with af in this cross,

nearly all ii seeds gave rise to af plants, but some crossovers were

recovered and the calculated linkage intensity between af and i was 3.72 in

the glasshouse population and 5.60 in the field populations (Table 4).

Af-af vs Am-l-am-1: These two genes were in repulsion phase and no

crossover plants were recovered in the F2 of either the glasshouse or field

populations (Tabie 4). This result is consistent with a previous study

(2) involving a comparable number of plants. In both cases progeny tests

were required to extract af - am-1 recombinants. In the present case, 32

am-1 F2 segregants were progeny tested and, of those, five progenies

segregated for Af-af, the estimated recombination fraction being 9 + 4% (vs

8+3% for the 1969 experiment).

Am-l-am-1 vs I-i: These two genes also were in repulsion and,

again, no am-1-i plants were recovered in F2 (Table 4). The progeny tests

which were performed to recover af-am-1 plants (described in previous

paragraph) were not all carried into the adult plant stage so no estimate

of the intensity of linkage between am-1 and i Is possible from these

studies, except that the combined F2 populations indicate that the value is

less than 13%. However, one crossover progeny was found among a group of

selected plants that were grown to maturity.

1. Blixt, S. 1972. Agri Hort. Genet. 30:1-293.

2. Marx, G. A. 1969. PNL 1:9-10.

3. Marx, G. A. 1972. PNL A:30-31.

4. Marx, G. A. 197A. PNL 6:30-31.

5. Marx, G. A. 1982. PNL 14:41-42.

6. Marx, G. A. 1983. PNL 15:43-45.



	50 PNL Volume 16 1984	RESEARCH REPORTS

	Cov Fs Evidence adduced previously has indicated that cov, a chlorophyll gene which confers a distinct blue-green foliage color (but without affecting pod color), is located on chromosome 5 in the vicinity of cr and gp (3,4). These results lead to the expectation, demonstrated herein, that cov should show evidence of linkage with fs (Table 2). Table 2. Analysis of the F2 of a repulsion phase cross Cov fs x cov Fs.



	A-Af-I-Am-1 Preliminary data on a cross involving three genes on chromosome 1 , af-i-am-1, was reported last year (6). Larger populations of the same cross were grown and evaluated in the field in 1983. In this case, however, the seeds from the F1 plants (i.e. F2 seeds) were sorted prior to planting for yellow (I) and green (i) cotyledon color. Because, as the analysis of the glasshouse populations demonstrated, the three genes are rather tightly linked, the I seeds, except for a few crossovers, were expected to produce plants with normal (Af/-) foliage but to segregate for A-a, for I-i, and for Am-l-am-1. The am-l/am-1 plants were expected to be I/I but only the A plants of this group are expected to show the seed disorder (sd-1) associated with am-1 (that is, sd-2 expression is blocked in the presence of a/a). The second group of seeds, the ii seeds, were expected to produce (except for crossovers) afila (af) plants segregating for A-a but not for am-1 and its as- sociated seed disorder. These expectations were fulfilled in the field populations (Tables 3 and 4), the only exceptions arising from crossover events.