Mendel's principles of heredity: A defence — John Shaqi
Mendel's principles of heredity: A defenceMendel, Gregor
Science
Mendel's principles of heredity: A defence
Mendel, Gregor
Heredity; Hybridization; Mendel's law; Weldon, Walter Frank Raphael. Mendel's laws of alternative inheritance in peas
These two experiments are important for the determination of the
average ratios, because with a smaller number of experimental plants
they show that very considerable fluctuations may occur. In counting
the seeds, also, especially in Expt. 2, some care is requisite, since
in some of the seeds of many plants the green colour of the albumen is
less developed, and at first may be easily overlooked. The cause of the
partial disappearance of the green colouring has no connection with the
hybrid-character of the plants, as it likewise occurs in the parental
variety. This peculiarity is also confined to the individual and is
not inherited by the offspring. In luxuriant plants this appearance
was frequently noted. Seeds which are damaged by insects during their
development often vary in colour and form, but, with a little practice
in sorting, errors are easily avoided. It is almost superfluous
to mention that the pods must remain on the plants until they are
thoroughly ripened and have become dried, since it is only then that
the shape and colour of the seed are fully developed.
Expt. 3. Colour of the seed-coats.--Among 929 plants 705 bore
violet-red flowers and grey-brown seed-coats; 224 had white flowers
and white seed-coats, giving the proportion 3·15 to 1.
Expt. 4. Form of pods.--Of 1,181 plants 882 had them simply inflated,
and in 299 they were constricted. Resulting ratio, 2·95 to 1.
Expt. 5. Colour of the unripe pods.--The number of trial plants was
580, of which 428 had green pods and 152 yellow ones. Consequently
these stand in the ratio 2·82 to 1.
Expt. 6. Position of flowers.--Among 858 cases 651 blossoms were
axial and 207 terminal. Ratio, 3·14 to 1.
Expt. 7. Length of stem.--Out of 1,064 plants, in 787 cases the
stem was long, and in 277 short. Hence a mutual ratio of 2·84 to
1. In this experiment the dwarfed plants were carefully lifted and
transferred to a special bed. This precaution was necessary, as
otherwise they would have perished through being overgrown by their
tall relatives. Even in their quite young state they can be easily
picked out by their compact growth and thick dark-green foliage.
If now the results of the whole of the experiments be brought together,
there is found, as between the number of forms with the dominant and
recessive characters, an average ratio of 2·98 to 1, or 3 to 1.
The dominant character can have here a _double signification_--viz.
that of a parental-character, or a hybrid-character[35]. In which
of the two significations it appears in each separate case can only
be determined by the following generation. As a parental character
it must pass over unchanged to the whole of the offspring; as a
hybrid-character, on the other hand, it must observe the same behaviour
as in the first generation.
Public-domain text, read in full here on John Shaqi.
Reviews
Reviews
No reviews yet
Be the first to share your thoughts on this work.
Join the Discussion
Join the discussion
Sign in to leave a comment or review.
Sign InorCreate an account