> Any ideas on why there are difference in the cases that do show
>them? I can see why there would some differences in F2 but what of
>F1 generation crosses?
A classical example of F1 differences are the monkey x horse bastards which
look different depending if the monkey or the horse was the female. The
german language has even two different words for the two mule forms
(Maulesel, Maultier).The reason is probably the fact that the chromosomes
are not the only heredity factors. Plasmatic factors also may influence
heredity and are only present in the female egg cell but not in the sperma
cells.
In plants the pollen cells usually contain some carbonhydrates while the
egg cells also contain proteins. These proteins are different from species
to species and may influence heredity.
Another reason of phenotypical differences are different chromosome numbers
of the parents. It seems that in some plants (e.g. Iris) certain hybrids
of unequal chromosome parents can only be produced in one direction.
Juerg
___________________________________________________
Juerg Steiger, Institut fuer Aus-, Weiter- und Fortbildung IAWF
University of Bern, Inselspital 37a, CH-3010 Bern, Switzerland
Office: +41 31 632 9887 Fax: +41 31 632 9871