Behavior of the nuclear elements in Zea mays

Material: Line X - Genotype C*-IE7002 A1 A2 C R Pr B Pl homozygous (#1877 Dr. Randolph, 1933), phenotype A C R Pr B Pl; Line Y - Genotype A1 A2 C R Pr homozygous (originating from the cross between c-tester and gl ij tester from Cornell University, 1934), phenotype A C R Pr.

Operation 1: (Line X x Line Y) x Line Y. F1 Phenotype A C R Pr B Pl; BC1 40 progenies, grains Pr = 10084, Pr dilute = 3179, colorless = 256; total = 13519; colorless grains = 1.8%. The percentage of variability of colorless grains between progenies was very small since 50% of the progenies fell within 1 to 2% colorless grains. The amplitude for colorless grains fell between 0.5 and 4%. The mean is 1.8%.

Interpretation: Mendelian interpretation is possible due to the homogeneity of the segregation among 40 BC1 progenies. The gene C*-IE7002 of Line Y with activators would produce free replicates (amplification) that would inhibit the aleurone color. Line X would carry the genes E1 E2 E3 E4 E5 besides the genes A1 A2 C R Pr B Pl C*-IE7002, each of them (E*) wouId degrade the free replicates of the gene C*-IE7002. The operations and experimental results with the genotypes previously mentioned are:

C*-IE7002 E1 E2 E3 E4 E5 A1 A2 C R Pr B Pl      x      + e1 e2 e3 e4 e5 A1 A2 C R Pr
Phenotype = A C R Pr B Pl by degradation                      Phenotype = A C R Pr
of the replicates C*-IE7002

F1 = C*-IE7002 + E1 e1 E2 e2 E3 e3 E4 e4 E5 e5 A1 A1 A2 A2 C C R R B B Pl PI
Phenotype = A C R Pr B Pl

All grains have aleurone color because of degradations of the replicates C*-IE7002.

Previously mentioned BC1 will segregate 1/2 C*-IE7002 +, and only 1/32 will carry genotype e1 e1 e2 e2 e3 e3 e4 e4 e5 e5, which do not degrade the replicate C*-IE7002 and for that reason will segregate 1/2 x 1/32 = 1/56% colorless grains according to experimental data.

Operation 2: From 256 grains colorless aleurone (Operation 1) were obtained 134 plants which were self-fertilized. Segregation for colorless grains between progenies from S1 showed a very large variability which is indicated in the following table:

51 progenies did not segregate colorless grains
15 progenies segregated 1 to 10% colorless
27 progenies segregated 11 to 20% colorless
13 progenies segregated 21 to 30% colorless
14 progenies segregated 31 to 40% colorless
4 progenies segregated 41 to 50% colorless
4 progenies segregated 51 to 60% colorless
2 progenies segregated 61 to 70% colorless
0 progenies segregated 71 to 80% colorless
1 progeny segregated 81 to 90% colorless
0 progenies segregated 91 to 100% colorless

All grains analyzed from the segregating progenies gave the following results: Pr = 8843, Pr dilute = 8307 and colorless = 5081. Besides the large variability in the segregations of colorless grains between progenies were produced spurious segregations such as large colorless areas in ears alternating with colored areas; variable segregations of colorless grains according to considered area; big glumes, viviparity, big grains and grains more reduced than brittle, scattered anthocyanic spots in the stalk and anthers; stiff leaf with distic position, zig-zag stalk and male sterile.

Interpretation: Perhaps free replicates of the C*-IE7002 gene in synaptic labile position (episomic) with diverse loci would produce spurious segregations.

Operation 3: Colorless grains from 51 progenies (5081 grains) in Operation 2 were self-fertilized and the 52 ears with colorless grains were crossed x Line Y, and then were self-fertilized. The F1 had all colorless grains with good expression. In F2 was obtained great variability in the segregation and expression of aleurone color; the dominant character of the aleurone color in F1 was changed to recessive in F2.

Interpretation: In S2 the dominant free elements for colorless aleurone would stabilize in some progenies because of allelic synaptic phenomena. In the F1 of the cross between the previously mentioned S2 (colorless grains) x Line Y, the colorless character is dominant, but in F2 new synaptic phenomena are produced along the Line Y loci with free C*-IE7002 elements. The new synaptic phenomena would change dominant inhibitor character of the aleurone color to recessive.

Operation 4: (Line X x Line Y) x Line Y (BC1) gave colorless = 6, Pr dilute 65, Pr = 205. From the colorless class, sub-line (a) gave in S1 colorless = 27, Pr = 250; in S2 from the colorless, colorless = 195, Pr = 75; in S3 from the colorless, colorless = 133, Pr = 42 (good expression). From the BC1 Pr class, sub-line (b) gave in S1 colorless = 69, Pr = 273; in S2 from the colorless, 5 ears gave all grains colorless and 5 ears segr. 3/4 colorless:1/4 colored (good expression).

Interpretation: One among 200 backcrosses has a free C*-IE7002 replicate able to produce a permanent chromosomal insertion or episomic transitionary state. The above phenomenon is produced in sub-lines (a) and (b) independently and both lines answer to mendelian monogenic segregation of the dominant inhibitory character of the aleurone color.

Luis Mazoti


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