F1 / F2 hybrids

Tim Eck teck11@embarqmail.com
Mon, 26 May 2014 20:04:44 PDT

I liked all the answers but I am compelled to add my two cents:
Hybrid is usually defined as a cross between two different breeding
populations and species is usually defined as a breeding population (in
essence).  But this might seem to imply that a hybrid is impossible by
definition.  Also, if you have two different geographically separated clades
of the same species that don't normally breed with each other, you might be
tempted to call them different species (by definition).
Clearly, the definitions are not very clear and are an attempt to cram a
portion of the natural world into simple concepts.  As such, you might
consider the concepts of species and hybrid to be non-disjoint - that is,
something that is a cross between two 'subspecies' of the same species would
be both a species and a hybrid.
Also, one way to visualize the quantitative differences between the F1 and
F2 hybrids is to consider the bell curves of any given trait (e.g. petal
length) in the two species and in the hybrids.   Each species has a mean and
standard deviation for the petal length and the mean petal length for the F1
and F2 hybrids will be each the average of the two species mean petal
lengths.  But the total variation of the F1 hybrid is expected to be close
to that of the species, while the total variation of the F2 hybrid is
expected to span that of both species.  Both are bell curves, but the F1 is
a steep, narrow curve while the F2 has a very broad curve, extending all the
way to the extremes of both species.

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