Nicholas Chun
Section B
Long Term Assignment
Discussion and Conclusions
The data show patterns that indicate a definite pattern in the inheritance of hybrid
characteristics. The number of offspring with a particular characteristic appears in a
fixed ratio, and this ratio does not change when hybrids for two different characteristics
are bred. In effect, all the characteristics studied show independent assortment. The
results show that plants hybridize in a ratio of 3:1 in the first generation. This suggests a
hereditary model for the Pisum plants. If A is taken as the dominant trait and a as the
recessive trait, then the pattern of inheritance is AA, 2Aa, aa. Both the sperm and the
egg characteristics are seen in the offspring, and thus there must be hereditary input from
two sources, which has lead to the double letter model.
If a hybrid with Aa hybrid characteristics is crossbred with a Bb hybrid plant,
then the ratio resulting offspring can be determined in a combination series. The progeny
will appear as AB, Ab, aB, ab, 2Abb, 2aBb, 2AaB, 2Aab, 4AaBb. This pattern shows
up as a 1:2:4 ratio for ab::AB::Ab, aB. Furthermore, if the descendants are analyzed for
B and A characteristics independently, it is found that both the BB:Bb:bb and AA:Aa:aa
relationships have the ratio of 1:2:1. This is very important because it means that if given
true breeding strains, it can now be predict exactly how many of each type of plant will
result.
These results and analyses are in opposition to work done by both Kartner and
Kolreuter. Kartner’s proposition that a plants characteristics must be taken altogether has
not held up in this study. The current model of inheritance proposes that all heritable
traits of the “mother” and “father” get mixed together in their offspring and that some
intermediate form of these traits will then appear in this offspring. Clearly, the data
shows this to be inaccurate. Instead, it appears that the new plants will display either the
dominant or the recessive trait. For example, if studying the form of seeds, each seed
will either be round or wrinkled. There will be no seeds that are wrinkled on one half and
round on the other.
This experiment further debunks the current theory of holistic inheritance because
the seven characteristics studied were inherited independently of one another. This means
that it is impossible to determine what color the unripe pods of a plant will be if, for
example, given the form of the seeds. Thus every plant should be viewed as a
combination of independent heritable traits, rather than one holistic collection of linked
characteristics. This is not, of course, to say that Kartner is a poor experimenter with bad
conclusions. The experiment involving the Phesolum plants shows that hybridizing
crosses will not always work out in a prescribed 3:1 ratio. Furthermore, work done on
the color of ornamental flowers supports Kartner’s proposal that hybrids take on
intermediate characteristics between the two parental strains. It is found that
crossbreeding red-flower and white-flower parental strains can lead to pink flowers,
white flowers with red spots, or red flowers with white spots.
Data such as these indicate that not all characteristics turn out with clear dominant
and recessive traits. It is possible that the cultivation of these ornamental plants over the
years has made it impossible to isolate true-breeding plants, and that the parental strains
being used are, in fact, already hybridized versions of some long lost grandparental strain.
Further experimentation must be done to develop a model that takes these outliers into
account and to show whether what is the true cause for not. A second
Of course, great care was taken in this experiment to ensure that the parental
strains were true breeding and that there was no cross-contamination among plants, but it
is possible that there was experimental error. However, by the law of large numbers, it
seems doubtful that any of this would have caused significant deviations. Enough plants
were used to ensure that the statistical effects would outweigh deviation due to this kind
of error. Solely if the parental strains had not been true breeding would there be
significant error in the data. Only if the parental stocks had not been true breeding would
there be significant error in the data. However, it is doubtful that for all seven
experiments, true breeding lines failed to get isolated as parental strains. Since the ratio
of trait segregation was the same in all seven experiments, it can be concluded that in fact
all the experiments had true breeding strains as parental stock. Even with all the plants
used, it would have been helpful to have even more experimental material. Most of the
calculations done are statistical and based on probability. As such, the larger the pool,
the more accurate the data and the analysis.
From the data collected, it can be determined that trait segregation does occur and
occurs independently of each other trait. The new model for inheritance suggested by
these findings contends that every offspring will inherit only one form of a heritable trait
from its parents, and that the inheritance of this trait is not affected, and will not affect the
inheritance of any other traits. This new theory has groundbreaking implications. If the
rule of segregating traits is valid, and an offspring can only inherit one form of a trait,
then it is possible that characteristics previously thought of as determined exclusively by
environment, such as the gender of an offspring, may in fact be a heritable traits.