Mendel's Paper: A Collaborative Hypertext
Section 6: The Second Generation of the Hybrids
Experiments in Plant Hybridization (1865)
by Gregor Mendel
The Second Generation From the Hybrids
Those forms which in the first generation exhibit the recessive character do
not further vary in the second generation as regards this character; they
remain constant in their offspring.
It is otherwise with those which possess the dominant character in the first
generation. Of these two-thirds yield offspring which display the
dominant and recessive characters in the proportion of 3:1, and thereby
show exactly the same ratio as the hybrid forms, while only one-third
remains with the dominant character constant.
The separate experiments yielded the following results:
For each separate trial in the following experiments 100 plants were selected
which displayed the dominant character in the first generation, and in order
to ascertain the significance of this, ten seeds of each were cultivated.
- Expt. 1. Among 565 plants which were raised from round seeds of the first
generation, 193 yielded round seeds only, and remained therefore constant in
this character; 372, however, gave both round and wrinkled seeds, in the
proportion of 3:1. The number of the hybrids, therefore, as compared with
the constants is 1.93:1.
- Expt. 2. Of 519 plants which were raised from seeds whose albumen was of
yellow color in the first generation, 166 yielded exclusively yellow, while
353 yielded yellow and green seeds in the proportion of 3:1. There
resulted, therefore, a division into hybrid and constant forms in the
proportion of 2.13:1.
In each of these experiments a certain number of the plants came constant
with the dominant character. For the determination of the proportion in which
the separation of the forms with the constantly persistent character results,
the two first experiments are especially important, since in these a larger
number of plants can be compared. The ratios 1.93:1 and 2.13:1 gave
together almost exactly the average ratio of 2:1. The sixth experiment
gave a quite concordant results; in the others the ratio varies more or less,
as was only to be expected in view of the smaller number of 100 trial plants.
Experiment 5, which shows the greatest departure, was repeated, and then in
lieu of the ratio of 60:40, that of 65:35 resulted. The average
ratio of 2:1 appears, therefore, as fixed with certainty. It is
therefore demonstrated that, of those forms which posses the dominant
character in the first generation, two-thirds have the hybrid-character,
while one-third remains constant with the dominant character.
- Expt. 3. The offspring of 36 plants yielded exclusively gray-brown
seed-coats, while of the offspring of 64 plants some had gray-brown and some
- Expt. 4. The offspring of 29 plants had only simply inflated pods; of the
offspring of 71, on the other hand, some had inflated and some constricted.
- Expt. 5. The offspring of 40 plants had only green pods; of the offspring
of 60 plants some had green, some yellow ones.
- Expt. 6. The offspring of 33 plants had only axial flowers; of the
offspring of 67, on the other hand, some had axial and some terminal flowers.
- Expt. 7. The offspring of 28 plants inherited the long axis, of those of
72 plants some the long and some the short axis.
The ratio of 3:1, in accordance with which the distribution of the
dominant and recessive characters results in the first generation, resolves
itself therefore in all experiments into the ratio of 2:1:1, if the
dominant character be differentiated according to its significance as a
hybrid-character or as a parental one. Since the members of the first
generation spring directly from the seed of the hybrids, it is now clear
that the hybrids form seeds having one or other of the two differentiating
characters, and of these one-half develop again the hybrid form, while the
other half yield plants which remain constant and receive the dominant or the
recessive characters in equal numbers.
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