"Kay Easton" wrote in message
...
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:
Kay,
Again you are quite correct.
Have you also noticed that blue flowers, when photographed, can often look
'magentarish'?
With all flowers the primary search is for the natural/ wild version. These
will be genetically pure~~ but not necessarily dominant~~ for all of their
genes, to any mutation that occurs. Mutations of genes do take place over
time and these can be dominant or recessive to existing alleles. Only when
it is expressed is it possible to determine dominance/recessive or even
mutual.
A mutated allele can exist for hundreds of years before being crossed with
another with a similar mutation before it can be expressed.
This is why no form of sexual reproduction can reproduce an exact copy.
Yes, we can buy seeds that are of a named variety but that means they are
pure genetically for the aspects that matter, but for literally thousands of
genes they can and do differ.
The genetics of the Cornflower you mentioned can be shown to be similar to
that of the bluebell though with even more pairs of alleles invoved.
The sought after blue rose will only be achieved when further mutations
happen or can be induced~~not that it would appeal to me.
I visit Swedish universities and two years ago some students showed me
some 'blue roses' but this had been achieved by watering with analine dyes!
I was amused but not deceived.
Interestingly, quite a number of human aspects are determined quite simply.
My brother is an albino[truly] and yet both parents were quite normal~~my
father quite dark.
Thus, as you know, both parets were 'Aa' for albinism. The cross was Aa x
Aa= AA:2Aa:aa[my brother] So I am twice as likely to be hybrid than pure!
Also, as albinism is rare, all my brother's children must be Aa.
Even more interestingly; we not only inherit our parents' genes but also
the surname of our father. If, given a surname, and then having no male
children, the name would die out.
Surnames were often aquired through ones home town, occupation or
appearance.
Via my work I found a friend called 'Bulstrode' which is not totally
uncommon. He was born with a deformed hip which is recessive. His
g.g.g.g.getc.parent must have aquired that name by [in Anglo-saxon] "walking
like a bull". Legs apart and swinging.
The allele being carried for a thousand years before his father with the Aa
unwittingly[and of course called Bulstrode] met another carrying the Aa,~
unknowingly.
Perhaps the loveliest girl I ever met is called Broadfoot, and has a club
foot. With modern appliances this can be reasonably disguised. Obviously her
ancestor was given that name because of that deformity. There was no PC in
those days. Human skin pigmentation involves numerous pairs of
alleles. The totally black being dominant for all invoved alleles. A single
pair of alleles becoming recessive dilutes the colour and explains all the
variations The combinations are seemingly endless.
Sorry to have been so garrulous but have taken time off to have a cold
and a tooth extracted. Being a man I consequently make a great fuss over
such a triviality!!
Regards and Best Wishes Brian.
Where were you when I wanted attentive students??
"Getting older is not so bad when you think of the alternative"!!
http://www.scarboro.demon.co.uk/edward/index.htm