In article , Brian
writes

Kay~ Many thanks. Your ratios are quite correct for a colour determined by
a single pair of alleles. As you say they would be 'AA' for a normal
bluebell, 'aa' for a recessive and 'Aa' for the bluebell that looks normal
but is hybrid. So Aa x Aa = 1AA: 2 Aa: 1aa[white]
Also as you state Aa x aa = Aa : aa. and again the difficulty would be in
recognising the Aa ~~ which is impossible.
However the white requires two pairs of recessive alleles and gives a ratio
of 15 : 1 and then only having crossed [or self pollinated] a pair of
dihybrids.
For example pure blue would be 'AABB' 'and the white 'aabb'. The first
cross would be dihybrids 'AaBb'. Crossing two of these is not terribly
complicated mathematically but does give a ratio of 15 coloured to 1 white.
AABB:2AABb:AAbb:2AaBB:4AaBb:2Aabb:
aaBB:2aaBb:aabb. So only the aabb will be white. Those showing the A&b can
be pink as can those showing a&B but differing slightly. Nine will look the
normal blue.
--
Thanks! I was wondering about this this morning on the basis of '1
recessive gene expressed = pink, 2 = white?' which is in effect what
you've said ... on the principle that there is a pair of pink and blue
colourings in plants that seem very interlinked - as in cornflower,
geranium and borage family. Cornflower usually blue but pink and white
varieties readily available, geranium typically blue or pink (forgetting
about magenta for the time being), borage family often showing both in
same inflorescence as in forget-me-not and lungwort.

Also many blue flowers when dried turn pink.

Thus simplistic explanation is that there are two pigments, one a pink
one, one a readily decaying one which in combination with the pink gives
blue, and also that they are governed by separate alleles so that you
often encounter pink forms of the mainly blue flower. You've just
confirmed the genetic bit in bluebells - is it the same mechanism in the
other examples?
--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm