Interaction of Genes for Flesh Color in Watermelon

Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] flesh color is controlled by several genes to produce red, canary yellow, salmon yellow, and orange. Our objective was to study the interaction of three gene loci with two or three alleles at each C (canary yellow vs. red), y (salmon yellow vs. red), yo (orange), and i (inhibitory to C permitting Y to produce red flesh color). Five crosses were used to study gene action: `Yellow Baby' × `Sweet Princess', `Yellow Baby' × `Tendersweet Orange Flesh', `Yellow Baby' × `Golden Honey', `Yellow Doll' × `Tendersweet Orange Flesh', and `Yellow Doll' × `Golden Honey'. Based on the performance of six generations (PA, PB, F1, F2, BC1A, and BC1B), the parents had the following genotypes: `Yellow Baby' = CCYYII, `Yellow Doll' = CCYYII, `Sweet Princess' = ccYY ii, `Tendersweet Orange Flesh' = ccyoyoII, and `Golden Honey' = ccyyII. Segregation of flesh colors in the progeny of the five families demonstrated that there was a multiple allelic series at the y locus, where YY (red) was dominant to yo yo (orange) and yy (yellow). Also, yoyo was dominant to yy. In conclusion, epistasis is involved in genes for the major flesh colors in watermelon, with ii inhibitory to CC (Canary), resulting in red flesh, and CC in the absence of ii epistatic to YY, producing canary flesh.

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. II. The mode of inheritance of spring versus winter growth habit

The study on the mode of inheritance of spring versus winter growth habit in Triticum monococcum is the first in a diploid wheat species. The results are discussed in light of the information available on the genetics and cytogenetics of this character in Triticum aestivum. Two spring habit and six winter habit lines were used in these investigations. Statistical analyses of progenies in each of these lines clearly established the true-breeding nature of all eight lines with respect to days to heading. Analysis of F1 and F2 results of crosses between the two spring habit lines 68 and 293 showed the following: (i) neither line carries winter habit alleles at any of the major gene loci determining growth habit; and (ii) four of five minor allele pairs determine the phenotypic differences between them. Monohybrid F2 and testcross ratios in crosses between spring habit line 68 and each of the six winter lines lead to the following conclusions: (i) differences between spring and winter growth habit in each cross are due to alleles of one major gene; (ii) the allele for spring habit is completely dominant to that for winter habit in each cross; and (iii) all these lines are genotypically identical or very similar at all modifying gene loci. These results imply that only one major gene determines growth habit in this species. Diallel (critical) crosses among the six recessive lines indicate that complementation does not occur in any of the F1's. Therefore, all these recessive genes represent mutations in the same gene. If these results are characteristic of all winter lines in Triticum monococcum, they permit the initial conclusion that only one major gene determines growth habit in this diploid species. This locus is in all likelihood the VrnI locus since it is the only one of the five major genes identified for growth habit, that is present in the A genome of Triticum aestivum. All six recessive lines respond to natural vernalization. This lends further support to our initial conclusion. Because the six recessive lines head at five different times we conclude that a multiple allelic series occurs at this locus. Specifically, at least three and probably five recessive alleles responsible for different heading dates among the winter lines, and at least one dominant allele for spring habit, occur at this locus.Key words: Triticum, complementation, quantitative, vernalization, alleles, multiple.

CONTROL OF ANTHOCYANIN SYNTHESIS IN PETUNIA HYBRIDA BY MULTIPLE ALLELIC SERIES OF THE GENES An1 AND An2

ABSTRACT A mutable allele of the An1 locus in Petunia hybrida has given rise to a multiple series of stable derivative alleles. Anthocyanin concentration in mature flowers of these mutants (an1 +/p/an1) decreases from the wild-type red to the recessive white in a continuous series. Anthocyanin composition changes regularly: the ratio of peonidin to cyanidin is 3.5 for an an1 +/+/an1 and 1.2 for an an1 +/p5/an1 mutant. Analysis of anthocyanins during flower development indicates that these differences in composition are due to the specific state of the An1 locus and not to anthocyanin concentration. Anthocyanin concentration in flowers of the allelic series for An1 correlates with the activity of the enzymes UDP-glucose: flavonoid-3-O-glucosyltransferase and SAM: anthocyanin-3′-O-methyltransferase. The same correlations were found for members of a comparable allelic series at the An2 locus. The possibility that the correlation between the enzyme activities is due to the occurrence of a multienzyme complex is discussed.

CYTOGENETIC ANALYSIS OF AN SD CHROMOSOME FROM A NATURAL POPULATION OF DROSOPHILA MELANOGASTER

ABSTRACT The discovery and the cytogenetic characterization of a new SD(Segregation Distorter) chromosome 2 from a natural population in Ranna (Sicily, Italy), SDRa, are reported. The main features of this chromosome are as follows: (a) it contains an SdRa gene with a moderate degree of segregation distortion (= 0.72), (b) a recessive female sterile gene, fs(2)TLM, responsible for modifications of the morphology and structure of the testes and ovaries is located at 89.7, (c) SDRa/SDRa males and females are viable but sterile, the females due to homozygosis of fs(2)TLM and the males because of homozygosis of a region containing the Sd locus, and (d) SDi/SDj combinations are fertile, thus suggesting that the different Sd factors found in natural populations constitute a multiple allelic series.——These data may indicate that each population containing SD chromosomes has evolved its own genetic architecture for the complex SD system, with specific modifiers and perhaps different Sd genes. The possibility of reconstructing the evolutionary pattern of the SDRa chromosome in the natural Ranna population after the model of CHARLESWORTH and HARTL (1978) and CROW (1979) is considered.