Tight Linkage between the Fin Locus for Plant Habit and the Z Locus for Partly Colored Seedcoat Patterns in Common Bean

Linkage between the Fin locus controlling plant habit and the Z locus controlling partly colored seedcoats in common bean (Phaseolus vulgaris L.) was studied in the F2 and F3 progenies from the cross `t virgarcus BC3 5-593' (determinate habit, virgarcus pattern of partly colored seeds, fin tz) × `Steuben Yellow Eye' (indeterminate habit, sellatus pattern of partly colored seeds, Fin t zsel). The heterozygous genotype zsel/z produces the piebald pattern of partly colored seeds, whereas Fin is completely dominate to fin. Selection was made in the F2 for crossover phenotypes: indeterminate habit with virgarcus seeds or determinate habit with piebald seeds. Linkage calculations were based on crossover genotypes confirmed by F3 progeny tests grown in the greenhouse. The recombination percentage between Fin and Z was 1.032±0.33 map units. The gene symbol zsel is proposed, where t Z gives the expansa partly colored seedcoat pattern, t zsel gives sellatus, and t z gives virgarcus.

Linkage analysis of open bud (ob2) and yellow petal (Y1) in cotton

In allotetraploid Gossypium species yellow petal is controlled by duplicate dominant genes Y1 (Ah genome) and Y2 (Dh genome), and open bud is controlled by duplicate recessive genes designated ob1 (Dh genome) and ob2 (Ah genome). Y2 and ob1 have been shown previously to be linked on chromosome 18 and 11.5 map units (MU) apart. In this study ob2 and Y1 were transferred from Gossypium darwinii (Watt) accession CB3099 into Gossypium hirsutum L. and found to have a mean recombination percentage of 3.14 for backcross and 3.40 for self-pollinated families from 2n parental heterozygotes and 10.73 in families from mono-18 parental heterozygotes. The lower recombination frequency in the homoeologous linkage group was perhaps due to this chromosome segment being transferred from G. darwinii. The higher frequency of recombination in the monosomic progeny families suggests that the absence of recombination in one homoeologue (chromosome 18) is compensated for by an increase in recombination in the other homoeologue.Key words: cotton, G. hirsutum L., homoeologous linkage groups, genetic markers.

APPLICATION OF THE OVARIAN TERATOMA MAPPING METHOD IN THE MOUSE

ABSTRACT Murine ovarian teratomas were used to determine recombination percentages for gene-gene and centromere-gene intervals. Data were obtained utilizing a recombinant inbred strain, LTXBJ, and a number of newly developed LT/SvEi congenic strains. ——Centromere-gene recombination was measured at 11.3 ± 1.2% for the centromere of chromosome 7 – Gpi-1 interval and 15.8 ± 2.4% for the centromere of chromosome 14 – Np-1 interval using the ovarian teratoma method. The centromere – Np-1 interval was measured at 26.5 ± 3.6% using a standard backcross involving the Rb6Bnr Robertsonian translocation as a centromere marker. ——To assess the accuracy of the ovarian teratoma mapping method, we compared the recombination frequency obtained for the Mpi-1–Mod-1 interval on chromosome 9 using the ovarian teratoma method to that obtained using a standard backcross. The recombination percentage was 22.9 ± 5.4 using the ovarian teratoma method and 18.6 ± 3.3 using the backcross method, indicating that the two methods produce equivalent estimates of recombination. In addition, for centromere-gene intervals known to be more than 30 cM in length, the ovarian teratoma method was consistent with classical recombination methods, yielding high recombination percentages. We conclude from these results that the ovarian teratoma mapping method is a reliable method for estimating recombination frequencies and the most accurate method available for estimating centromere-gene recombination frequency in the mouse.

RECOMBINATION AT THE Ml-a LOCUS IN BARLEY CONDITIONING RESISTANCE TO ERYSIPHE GRAMINIS F. SP. HORDEI

Attempts were made to recombine the dominant or semidominant resistance genes Ml-a, Ml-a3, Ml-a8 and Ml-a9 from the barley varieties Algerian Ricardo, Heil's Hanna and Monte Cristo, respectively. No recombinants with two resistance genes in the coupling phase were found in a total of 3117 test-cross seedlings from four crosses studied. The true recombination percentages between the genes Ml-a/Ml-a3, Ml-a/Ml-a8, Ml-a/Ml-a9 and Ml-a8/Ml-a9 are between zero and 0.5. One possible recombinant susceptible to Erysiphe graminis f. sp. hordei suggests that the recombination percentage between the recessive genes ml-a/ml-a8 is 0.083.

Zur Kinetik der Rekombinantenbildung bei T 1-Bakteriophagen

A cross is made between 2 mutants of phage T 1 with a multiplicity of infection of 4 of each type. Infected bacteria are opened during the latent period after the method described by Doermann, and recombinant percentages are determined. From the increase of recombinant frequency and the increase of particle number, the recombination percentage and the mating experience of the particles in the pool are calculated, making use of the equations of the Delbrück-Visconti theory. From the linear increase of mating experience follows constant mating probability between 8 and 14 min after infection. It is shown in the discussion that the beginning of mating occurs very likely at 4 min. The mating probability is constant over the entire length of the latent period, thus being independent of the pool size.