matters is too hazardous to be profitable.

* * * * *

{88}

CHAPTER IX

REPULSION AND COUPLING OF FACTORS

Although different factors may act together to produce specific results in
the zygote through their interaction, yet in all the cases we have hitherto
considered the heredity of each of the different factors is entirely
independent. The interaction of the factors affects the characters of the
zygote, but makes no difference to the distribution of the separate
factors, which is always in strict accordance with the ordinary Mendelian
scheme. Each factor in this respect behaves as though the other were not
present.

A few cases have been worked out in which the distribution of the different
factors to the gametes is affected by their simultaneous presence in the
zygote. And the influence which they are able to exert upon one another in
such cases is of two kinds. They may repel one another, refusing, as it
were, to enter into the same zygote, or they may attract one another, and,
becoming linked together, pass into the same gamete, as it were by
preference. For the moment we may consider these two sets of phenomena
apart. {89}

One of the best illustrations of repulsion between factors occurs in the
sweet pea. We have already seen that the loss of the blue or purple factor
(B) from the wild bicolor results in the formation of the red bicolor known
as Painted Lady (Pl. IV., 7). Further, we have seen that the hooded
standard is recessive to the ordinary erect standard. The omission of the
factor for the erect standard (E) from the purple bicolor (Pl. II., 5)
results in a hooded purple known as Duke of Westminster (Pl. II., 7). And
here it should be mentioned that in the corresponding hooded forms the
difference in colour between the wings and standard is not nearly so marked
as in the forms with the erect standard, but the difference in structure
appears to affect the colour, which becomes nearly uniform. This may be
readily seen by comparing the picture of the purple bicolor on Plate II.
with that of the Duke of Westminster flower.

Now when a Duke of Westminster is mated with a Painted Lady the factor for
erect standard (E) is brought in by the red, and that for blue (B) by the
Duke, and the offspring are consequently all purple bicolors. Purples so
formed are all heterozygous for these two factors, and were the case a
simple one, such as those which have already been discuss