Crossing Over in the Third Linkage Group in Oenothera

Abstract

In O. lamarckiana the gene for double flowers (mut. supplena) and 1 of the genes for old-gold flower color (mut. vetaurea) are the only known genes of the 3rd linkage group. This paper reports the 1st crossing over between these 2 genes. Double-dominant yellow singles (31) in an F2 family consisting of 94 yellow singles and 22 old-gold doubles were backcrossed to one of their double-recessive old-gold double sibs; 10 of the 31 F3 families contained only yellow singles, the parents having been homozygous, while 21 families consisted of 946 yellow singles, 810 old-gold doubles, and 1 yellow double, a crossover ratio of 0.057%. Other backcross families (15) consisted of 411 yellow singles, 449 old-gold doubles, 6 yellow doubles and 2 old-gold singles, a crossover ratio of 0.92%. Families (12) from selfed diheterozygous yellow singles produced 789 yellow (or sulphur) singles, 221 old-gold doubles, 5 yellow doubles and 5 old-gold singles,[long dash]a crossover ratio of about 0.95%. Crossing over in Oenothera is not related in this case to the arrangement of non-homologous chromosomes into circles, but consists in the transfer of genes from one chromosome to the other of the same pair,[long dash]an "intrazygous" process, not a "synzygous" one. In the 1st block of 31 families above mentioned, rubricalyx bud-color and the lamarckiana lethals (both linkage group I) were also present in the heterozygous state. The total of these 31 progenies consisted of 3010 rubricalyx (red buds) and 5 pervirens (green buds), representing a crossover of 1.85% between this pair of bud-color genes and one of the zygote lethals.