Elective Expression and Variegation
Wright: Dwarf Prairie Rose (1937)
The foliage of my thirty-nine hybrids [Hansa x Rosa suffulta] formed a most interesting study. Variation
was all the way from Suffulta to Rugosa, and with some the size of the Rugosa
leaf was combined with the type of Suffulta.
Amateis (1961)
So far I have found that primary crosses in rhododendrons produce quite variable seedlings, breaking up in what would appear to be second generation segregation. Unlike the well-behaved pea and snapdragon of Mendel, they refuse to lend themselves to neat little mathematical ratios. On only one occasion have I seen consistent uniformity in a primary cross. This was a Leach cross, catawbiense album Glass x yakushimanum. It was a joy to behold. All so uniform in height that they looked sheared and each smothered with its merry pink buds and white blossoms.
Burbank: Hybrid of Tomato and Currant Tomato (1914)
The fertilization was effected without difficulty, and an abundant supply of seed was produced. The hybrids that grew in the next generation were many of them pretty clearly intermediate in form and appearance between the parents. But some of them were almost ludicrous in appearance. They took on twisted and contorted forms, and in particular their leaves were curled and twisted into fantastic shapes.
As to fruit, some of the plants produced long clusters with tomatoes much larger than cherries; others furnished small fruit like that of one of the parents. And in some cases a plant that had retained the short stocky tree form of the common tomato bore clusters of small tomatoes in bunches similar to those of the other parent.
The foliage varied astonishingly between the two types. In some there was an exact compromise that was very curious. The dark, blistered leaves of the ordinary tomato, combined with the long, slender leaves of the currant tomato, produced a most interesting effect. Other specimens showed every possible gradation between the parent forms.
Here, then, was a case in which there was no conspicuous dominance of one parent or the other as regards any individual character that could be segregated and classified.
Neither as to size and form of plant-stalk, nor as to leaf, nor as to the fruit itself, was there clear prepotency or dominance of one parent over the other.
Edwards's Botanical Register, 8 (1846)
When the bright yellow flower of the white turnip is crossed with the dull golden of the Swede, an intermediate colour is not obtained, but some of the mules (as to the colour of the flower) follow one parent, and some the others.
Noble: Clematis jackmanii alba (1888)
The flowers produced from the old wood during the months
of May, June and July, are double or semi-double, solitary, and of a bluish
French gray; while those produced from the young shoots, in August and
September, are single and white, in pairs on a long raceme, showing as many as
ten pairs and a terminal on a string.
Brown: Form and Structure of Certain Plant Hybrids (1913)
In the great majority of cases the cells of the hybrids studied were intermediate between the corresponding cells of the parents. This indicates that there must have been a complete blending of parental elements. But exceptional cases showed that a blending had not taken place, or if it had, it must have been followed by a segregation of characters. For instance, certain epidermal cells of the calyx of the Calceolaria hybrid [Calceolaria hybrida x C. integrifolia] formed glandular hairs, and other epidermal cells simple hairs, one parent having glandular hairs on its calyx and the other simple only.
A hybrid between Wild Goose Plum and Troth's Early Peach showed that segregation had advanced a step farther; whole patches of epidermal cells of the twigs were exactly like the epidermal cells of either parent. Hildebrand (1889) reports an interesting case of segregation taking place within a single cell. In a hybrid between Oxalis latifolia and O. tetraphylla he found the characteristic hairs of the two parent species might both arise from a single epidermal cell of the hybrid.
Lysenko: "Maternal" Hybrids in Wheat (1954)
In 1939, the offspring
of these first-generation plants, the "legitimate hybrids"
(i.e., the awnless), as well as the offspring of four awned plants, were
planted separately at Gorki Leninskiye, the Experiment Base of the Lenin
Academy of Agricultural Sciences of the U.S.S.R. I will not deal here with the
question of how the progeny of the different first-generation plants
varied, because the analysis is not yet complete. Suffice it to say that in the
second generation, the progeny of one of the four awned plants (i.e., those
that had seemed to be of the purely maternal type) produced several plants with
characters which in many ways resembled those of the paternal form Lutescens
062. Of the 180 plants in the progeny of this plant, 172 were found to be of
winter habit resembling the maternal form, and 8 of the plants eared; 5 of
these were awnless and 3 were awned.
Meehan (1900)
Fuchsia fulgens had been introduced a year or so before, and someone sent my father a few flowers. I was the "garden boy" under my father. Fond of garden experiments, I had decided to repeat Knight's work in hybridising garden Peas, when the large amount of pollen on the Fuchsia flowers interested me. It was applied to the stigma of Fuchsia longiflora. From the one berry that resulted several dozen plants were raised. The largest and best of these subsequently appeared in the trade through the agency of Youell & Co., of Yarmouth, as 'St. Clare.' An interesting lesson followed. From this one berry no two of the many seedlings were alike. Some nearly approached the female, some the male; none could fairly be said to be intermediate. It was evident that the action of the pollen had not alone to do with the variation. Some physiological force, to this day not understood by me, must have been co-ordinate in the production of these results.
On Imperfect Hybridity.
Isaac Anderson-Henry, Esq. (1872)
Among the same batch of seedlings from which I obtained Veronica Andersonii,—V. salicifolia (syn. V. Lindleyana) + V. speciosa,—came one which, to all appearance, was a reproduction of the male parent pure and simple. And deeming it nothing else, I presented it to a friend, V. speciosa being then comparatively a new plant; and he, when he flowered it, came to tell me that it had come a very different thing in bloom to the true V. speciosa, having much longer flower-spikes and of a much lighter colour than those in that species, being of a light crimson instead of a dark purple, as in the V. speciosa.
Pearson & Lee: Intermittent Prepotency (1903)
While we
suppose unit prepotency,—the tendency of one individual out of a pair to be
prepotent,—to be chronic, there
is another form of prepotency which we may describe as intermittent. One or other parent may at a particular
mating, or may in certain individual offspring of one and the same mating, be
prepotent. On another occasion, or in other offspring of one and the same
mating, it may not be prepotent or even the other parent may be prepotent. Such
prepotency might exhibit itself in "alternative" or
"exclusive" inheritance, and is distinct from any unit prepotency or
absolute or partial dominance. It does not depend on the possession by one mate
of certain characters, but on the condition of the parents and other
circumstances peculiar to a special mating.
Experiment Station Record, 30: 144 (1914)
On some hybrids of Vitis vinifera and V. berlandieri, GARD (IV. Conf. Internat. Génétique Paris, Compt. Rend, et Raps., 1911, pp. 395, 396).
In studying a number of hybrid forms of V. berlandieri X V. vinifera raised from seed of V. berlandieri it was observed with regard to the stem that the hairy character of the maternal parent and also the glabrous character of most varieties of V. vinifera occurred among the hybrids) together with a large number of intermediate forms. Transverse sections of the stem show that the structure is sometimes intermediate between the two parents and sometimes nearer that of V. vinifera. Most generally certain characters of the liber and of the secondary wood, and especially those of the primary wood, are nearer V. vinifera. In the roots, on the other hand, these characters are nearer the other parent and are in accordance with the power of resistance to phylloxera and the excellent qualities as stocks possessed by these hybrids.
Melons (Sageret, 1826)
"The assumed product of the crosses made ought to have been intermediate: (1) Flesh very pale yellow, (2) seeds very pale yellow, (3) netting light, (4) sides slightly marked, (5) flavor at once sweet and sprightly, but the contrary was the case.
As a matter of fact, in the two hybrid fruits reported upon, the characters were not blended or intermediate at all, but were clearly and distinctly those of one or the other parent."
Datura (Naudin, 1865)
“He has confirmed that
which Sageret already knew, that in a hybrid the characters of the two parents
are often shown, not blended but approximated, in such fashion that the fruit
of a Datura hybrid, born of
two species, the one with a smooth, the other with a spiny capsule, presents
smooth places in the midst of a surface generally spiny. This disjunction, as
it is called, is explained according to him by the presence in the hybrid of
two specific essences, which tend to be separated more or less rapidly the one
from the other.”
It is of further of great
interest to note that the seeds gathered from the smooth side of the capsule
reproduced only the smooth-capsule form, Datura laevis, while those taken from the spiny side gave rise
only to the spiny form, Datura stramonium.
Dogs, pigs, stocks (Darwin, 1865)
According to Rengger, the hairless
condition of the Paraguay dog is either perfectly or not at all transmitted to
its mongrel offspring; but I have seen one partial exception in a dog of this
parentage which had part of its skin hairy, and part naked; the parts being
distinctly separated as in a piebald animal. When Dorking fowls with five toes
are crossed with other breeds, the chickens often have five toes on one foot
and four on the other. Some crossed pigs raised by Sir R. Heron between the
solid-hoofed and common pig had not all four feet in an intermediate condition,
but two feet were furnished with properly divided, and two with united hoofs.
Analogous facts
have been observed with plants: Major Trevor Clarke crossed the little
glabrous-leaved, annual stock (Matthiola), with pollen of a large,
red-flowered, rough-leaved, biennial stock, called cocardeau by the French, and the result was that half the
seedlings had glabrous and the other half rough leaves, but none had leaves in
an intermediate state. That the glabrous seedlings were the product of the
rough-leaved variety, and not accidentally of the mother-plant's own pollen, was
shown by their tall and strong habit of growth. In the succeeding generations
raised from the rough-leaved crossed seedlings, some glabrous plants appeared,
showing that the glabrous character, though incapable of blending with and
modifying the rough leaves, was all the time latent in this family of plants.
Orange x Pomelo
(Swingle & Weber, 1897)
FIG. 10—Leaves of orange and pomelo and
of their hybrids of the first generation, showing close resemblance to one or
the other parent: f, St. Michael Blood (Citrus
aurantium), female parent m, Bowen pomelo (C. decumana),
male parent; hf, hybrid, resembling female
parent hm, hybrid, resembling male parent.
Citrus x Poncirus
(Swingle, 1911)
The citremons, or crosses between the lemon and Citrus
trifoliata, on the contrary, show nearly 20 per cent of seedlings with an
exaggerated development of hypophylls, and in the majority of cases never
produce any normal foliage leaves at all, dying from starvation shortly after
the reserve food material of the seed is used up. One parent, Citrus
trifoliata, has a few hypophylls along the base of the stem of the young
seedling, while the lemon, like the orange and all other common citrous fruits,
shows a pair of rather large, rounded, sessile, opposite leaves. Some show five
leaflets (this occasionally occurs in citranges also), others show unifoliate
leaves or leaves with very much reduced side leaflets (which is rarely or never
seen in citranges). Most of the citremons have trifoliate leaves with large
lateral leaflets, which is the type characteristic of citranges.
Paphiopedilum (Hurst,
1900)
When several hybrids from
the same pair of species are compared together, this variation of the parts, of
“Partial Prepotency,” as I propose to call it, becomes even more apparent and
more diverse. For example, in three hybrids raised from the same parents, in
the first, the pollen-parent may predominate in form in a certain part; in the
second, the seed-parent may prevail in that part; while in the third, that part
may be fairly intermediate between both parents; while in regard to colour,
these conditions may be exactly reversed. But this only includes one part of
the hybrid, and the same law applies equally to every one of the parts so that
when the changes are rung on twenty or more different parts by the two parents
in both form and colour, we can well understand the many possibilities of
variation in hybrids of the same parentage; and I venture to suggest that this
law of Partial Prepotency, founded on actual facts observed in hybrids of
Paphiopedilum, may perhaps throw some light on the question of variation in
offspring of the same parents. Yet, notwithstanding this variation in the
parts, it is a remarkable fact that in primary hybrids the whole plant taken
together is fairly intermediate between the two parents, the balance of power
being well maintained in the whole.
Peas, Datura (Sutton, 1903)
If each cell contains maternal and paternal potentialities in regard to each character, and if dominance is not a common function of one of these, there is nothing to show why as a result of some disturbing factor one body of chromatin may not be called into activity in one group of cells and its homologue in another. This would produce just the sort of a mosaic which Bateson and Saunders found in Datura or as Tchermak's pied yellow and green peas obtained by crossing the Telephone pea with yellow varieties. Correns describes the condition as poecilodynamous and his conception of the causes of the phenomenon as I understand it is parallel with that which I have outlined above. The logical possibility suggested by Bateson that the recessive islands in such cases as the mosaic pea may be due to recessive allelomorphs in the paired state does not accord with the theory of a chromosomic basis for those allelomorphs, since the chromosome groups, both of cells showing the recessive character and of neighboring cells showing the dominant one, are derived, so far as we know, by longitudinal or equation division from the chromosomes of the same original cleavage nucleus and hence must be alike.
Veronica (De Vries,
1904)
In my garden, I cultivated, for many years, a Veronica
longifolia which was a hybrid
from the blue species and the white variety, and correspondingly had blue
flowers. But from time to time splittings occurred; either one single spike
bloomed white, or a few isolated white flowers appeared on an otherwise blue
spike. During the entire life, up to the time of the formation of the
reproductive cells this internal dualism manifests itself in this way.
Sometimes proofs of it are even found in the anatomical structure of the
tissues, and of the individual cells, where the parental characters are set
free and a mosaic-like structure results. MacFarlane, who has made the most
thorough study of the anatomical structure of hybrids, recognizes everywhere
the principle of duality, and goes so far as to regard every individual
vegetative cell of a hybrid as a hermaphrodite formation. And the renowned
French investigator of hybrids, Naudin, also expressed himself about forty
years ago in a similar manner. "L'hyhride est une mosaique
vivante," said he; we do not
recognize the individual parts as long as they remain intimately blended, but
occasionally they separate and then we are able to distinguish them.
We therefore regard it as established
that, in the children, the inheritances from the fathers and mothers are indeed
combined, but not fused into a new entity. Acting always conjointly under
ordinary circumstances, they yet do not lose the power of separating
occasionally.
Cistus (Gard, 1911)
Cistus ladaniferus x C. monspeliensis.—15 hybrids were obtained, and one plant
resembling the seed parent. The former consisted of two types, one of which
nearly resembled C. ladaniferus and the other C. monspeliensis.
C. albidus x C. polymorphus subsp. villosus.—170 hybrids were obtained. Some of these
possessed the leaf characters of the seed parent, others those of the male
parent, while a third category consisted of intermediate forms.
Sea Urchins, etc. (Loeb, 1912)
It is well known that Herbst and Tennent have made experiments in which the paternal influence in the hybrid embryo was diminished. Tennent states that in the cross between Hipponoe and Toxopneustes, Hipponoe characters become dominant in sea water of a high OH concentration and Toxopneustes characters in sea water of a low OH concentration. The amount of acid or alkali Tennent needed to accomplish his result was very small; namely about 2 cc. N/10 acetic or hydrochloric acid to 500 cc. of sea water.
Burbank: Variegated expression of purple and green in plum leaves (1914)
This is a crossbred seedling, descended from purple-leaved and green-leaved ancestors. The segregation of colors in the second generation has been referred to, and is illustrated here in a very interesting way. Most specimens have leaves that are all green or all purple; but here and there one mixes the colors, in a way that has peculiar interest for the student of heredity.
Radish x Cabbage
(Karpechenko, 1924)
"The radish-cabbage hybrids towards autumn appeared to be strictly
polymorphic in their habit of growth and, irrespective of difference in the
variety of cabbages participating in the crossing, were generally of three
types. The 1st type was a small plant
with a very short stem about 30 cm. in length, densely covered, especially at
the base, with small leaves; the stem was often branched and bore short
flowering shoots 15-17 cm. in length with clustered flowers. The 2nd
type of plant consisted of big leafy rosettes
of 1 1/2 metres in diameter, or bushes with short
thick branches and big leaves. They flowered sometimes, developing small
clusters of flowers. The 3rd type was represented by plants of a vigorous growth with a strong stem with many
branches of 2-2 1/2 metres in height. They flowered
abundantly and their flowering shoots reached a length of 1 1/2 metres and more."
Drosophila (Serra, 1949)
HETEROCHROMATIN POSITION EFFECTS
These constitute one of the most interesting types of position effects. In
what concerns the phenotype they provoke are of the mimic class, but in many
cases they show an additional characteristic, mottling or variegation. After
the first case of variegation was explained as an effect of the
"wild" allele being relocated in the chromocenter in the salivaries
(Schultz 1936) many other cases of mottling have been demonstrated to have this
causality. The variegation appears in heterozygotes, where the mutant loci
corresponding to genes contained in the segments inserted near the heterochromatin
may manifest in some patches of tissue, while adjacent ones remain of the wild
type or of an intermediary phenotype between the + allele and the extreme
recessive mutant. However, not always does the neighbourhood of heterochromatin
near + alleles causes variegation: sometimes there is a uniform phenotype like
the recessive
Japanese-Siberian
hybrid Iris (Hensler, 1992)
The first crosses were made in 1992 using 2 JI pod parents
(2n=24) and 2 Siberian pollen parents (2n=28). Seeds from 3 pods gave me 2
distinctly different types of fertile hybrids.
Chromosomes
were counted on 4 of the F1s (2 of each seedling type). Three of these showed
2n=26. One showed 2n=24.
The F1 "A" types appeared
to be pure species Ensata except for behavior. These plants prefer the growing
conditions of Siberians and are at their best when given good soil and water
with good drainage. Most of the F1 "B" types appeared to be pure
Siberian. Two individuals however, showed non-typical ridges in their leaves
once established and preferred the growing conditions of the JIs.