RADIATION INDUCED RECIPROCAL TRANSLOCATIONS AND INVERSIONS IN ANOPHELES ALBIMANUS

Reciprocal translocations and inversions were induced in Anopheles albimanus Wiedemann by irradiation of males with X rays. A total of 1669 sperm were assayed, and 175 new aberrations were identified as follows: 102 reciprocal translocations (67 autosomal and 35 sex-linked), 45 pericentric inversions, and 28 paracentric inversions. Eleven of the translocations were nearly whole-arm interchanges, and these were selected for the construction of "capture systems" for compound chromosomes. Two double-heterozygous translocation strains and four homozygous translocation strains were established. Anopheles albimanus females were irradiated, and a pseudolinkage scheme involving mutant markers was employed to identify reciprocal translocations. The irradiation of females was very inefficient: only one translocation was recovered from 1080 ova tested.

INCIPIENT GENOME DIFFERENTIATION IN GOSSYPIUM. II. COMPARISON OF 12 CHROMOSOMES IN G. HIRSUTUM, G. MUSTELINUM AND G. TOMENTOSUM USING HETEROZYGOUS TRANSLOCATIONS

ABSTRACT Eight homozygous translocation lines (TT) of G. hirsutum marking 3 chromosomes of the A genome and 9 chromosomes of the D genome were crossed with G. hirsutum, G. mustelinum and G. tomentosum, all homozygous for the standard end arrangements (tt). Chiasma frequencies in the G. hirsutum Tt controls were compared with those in the G. hirsutum × G. mustelinum and the G. hirsutum × G. tomentosum Tt hybrids. Both nucleus-wide and regionspecific chiasma frequencies were compared.—Some genome differentiation appears to have arisen between G. hirsutum and G. mustelinum. The G. hirsutum × G. mustelinum hybrids had a 1.8 to 1.9% reduction in the nucleus-wide chiasma frequency. Four of the eight TT lines showed a 3.4 to 10.5% reduction in chiasmata in the hybrid translocation quadrivalents, suggesting that chromosomes 1, 21, 23 and 24 may have undergone localized genome differentiation. The two species may differ naturally in the end arrangement of two chromosomes, since a quadrivalent not due to experimentally introduced translocations was observed in 13% of the PMC's of two G. hirsutum × G. mutelinum hybrids.—Very little genome differentiation has occurred between G. hirsutum and G. tomentosum. In the G. hirsutum × G. tomentosum hybrids, the nucleus-wide estimates showed only a very small (0.1 to 0.2%), though statistically significant, lowering of the chiasma frequency, and there was no reduction in chiasma frequency in the more sensitive readings for specific translocation quadrivalents.

ASSOCIATION OF PINK ALBINO SEEDLINGS WITH A RADIATION-INDUCED TRANSLOCATION OF CUCUMBER

Pink seed, which germinated faster than normal seed and gave albino seedlings with a pinkish color, segregated from all selfed fruit from plants of cucumber (Cucumis sativus L.) heterozygous for a radiation-induced translocation. The segregation ratio in some populations suggested monogenic, recessive inheritance. No pink seed or pink albino mutants segregated from fully fertile progeny of translocation heterozygotes and no homozygous translocation lines were found. It is suggested that the lethal albino mutation is associated with the induced interchange.

GENETIC ANALYSIS OF THE RECIPROCAL TRANSLOCATION T2(I;VIII) OF ASPERGILLUS USING THE TECHNIQUE OF MITOTIC MAPPING IN HOMOZYGOUS TRANSLOCATION DIPLOIDS

ABSTRACT A UV-induced sulphite-requiring mutant (sD50) consistently shows mitotic linkage to groups I and VIII in haploids from heterozygous mapping diploids. This linkage was found to be due to a reciprocal translocation T2(I;VIII) which could not be separated from the sulphite requirement in about 100 tested progeny from heterozygous crosses, and both may well have been induced by the same mutational event. T2(I;VIII) is the first case of a reciprocal translocation in Aspergillus which showed meiotic linkages between markers of different linkage groups, and, in addition, involved chromosome arms containing markers suitable for complete mapping by the technique of mitotic recombination in homozygous translocation diploids.—Using various selective markers, haploid segregants and diploid crossovers of all possible types were isolated from homozygous translocation diploids. (1) Haploid segregants showed new linkage relationships in T/T diploids: all available markers of VIII now segregated as a group with the majority of the markers of I, exceptfor the markers of the left tip of I. These formed a separate linkage group and are presumably translocated to VIII. (2) Diploid mitotic crossovers confirmed this information nd shhowed that the orientation of the translocated segments was unchanged. These findings conclusively demonstrate that T2(I; VIII) is a reciprocal translocation due to an exchange of the left tip of group I with the long right arm of group VIII.—Since the position of the break on VIIIR was found to be at sD50 this marker could be used to map the break on IL by meiotic recombination in heterozygous crosses. In addition, such crosses showed reduced recombination around the breaks, so that it was possiblc to sequence markers which normally are barely linked.