Inheritance of sex in Lychnis

Shull, George Harrison (February 1910) Inheritance of sex in Lychnis. Botanical Gazette, 49 (2). pp. 110-125.

DOI: 10.1086/330128


Hermaphrodite mutants occur in pure-bred families of Lychnis dioica L., the ratio of mutability being somewhat less than 1:1000. None of these hermaphrodites was diseased and several were fully functional both as females and males, thus negativing the suggestion of STRASBURGER that the hermaphrodites in this species may always be due to the attacks of the smut, Ustilago violacea. In their hereditary relations these hermaphrodites were of two kinds, some behaving like normal males, others having the capacity of transmitting the hermaphrodite character to their male offspring. This second class of hermaphrodites when self fertilized, or crossed with normal females, gives progenies consisting of normal females and hermaphrodites, and when fertilized by normal males gives normal females and normal males. The hermaphrodite individuals are modified males, for in all families in which these hermaphrodites were the pollen parents the offspring showed the same ratios of females and hermaphrodites as would have been expected of females and males had a normal male been used as the pollen parent. These results agree in a general way with those of Bryonia in that they demonstrate the homozygous character of the females and the heterozygous character of the males in Lychnis. Whether the females are positive or negative homozygotes cannot be determined from the F_1, as both assumptions can be made to fit the facts by the aid of simple correlative hypotheses whose correctness or incorrectness can be determined only by further breeding. A fundamental difficulty in either case is found in the fact that the egg cells of the hermaphrodites are apparently of a single type, all possessing the female-producing gene. The assumption that the hermaphrodites are heterozygous leads us to expect equal numbers of two different types of egg cells. Cytological studies may perhaps explain this difficulty, The male germ cells of the same plants are of two types, as required by theory. The occurrence of two hermaphrodite individuals in a progeny produced by a cross between hermaphrodite and normal male suggests the possibility that the hermaphrodite character may also be transmitted through the female. This fact, together with the occurrence of two genotypes among the hermaphrodites, is held to be slightly favorable to the view that the female is a positive homozygote. The demonstration that the hermaphrodite individuals of Lychnis are modified males indicates that STRASBURGER was mistaken in assuming that his hermaphrodites were diseased females. They were probably diseased males in which the dominance of the male character was modified by the fungus. The sex ratios in Lychnis do not accord well with a theory of sex which requires males and females to be present in equal numbers. The ratios found in my cultures are in accord with those found by STRASBURGER, the average for the past year being 1.32 females to 1 male, with a very wide difference in the ratios of different families. The significance of these ratios is not yet understood. When the variability in the sex ratios is compared with that in ratios produced by crossing heterozygous purple with white-flowered individuals, it is found that not only is there an undue departure in the sex ratios from the expected ratio 1:1, but also that there is greater variability in the sex ratios than in the color ratios, and that the curve is strongly negatively skewed and possibly not monomodal; while the color curve derived from the same families is nearly normal; with the mean departing but little from the 50 per cent. required by Mendelian theory.

Item Type: Paper
Subjects: evolution
CSHL Authors:
Communities: Station for Experimental Evolution at Cold Spring Harbor
Depositing User: Matt Covey
Date: February 1910
Date Deposited: 15 Jan 2013 14:15
Last Modified: 02 Nov 2017 14:57

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