16 April 2022 | New Scientist | 55Answers
Quick quiz #147
Answers1 Asteraceae, commonly known
as the daisy family2 The Compton effect3 The Holocene4 Sumer5 JupiterQuick Crossword
#105 AnswersACROSS 5 Mother, 7 Philtrum,
9 Plumbago, 10 Armpit,
11 Perspiration, 13 Planck,
15 Crater, 18 Edward Teller,
21 By-pass, 22 Taconite,
23 Foreskin, 24 Eye capDOWN 1 Phi-meson, 2 Argali,
3 Vitamin C, 4 Stamen,
6 Oil wells, 7 Prozac, 8 Unit,
12 Dementia, 14 Kawasaki,
16 Allen key, 17 Proton,
18 Enamel, 19 Ticker, 20 Typo#162 Poker dice
SolutionThe opposing faces of a die
always add up to 7. Therefore,
the die that is on the extreme
right must present 5 to the
adjoining cube.The central five dice contribute
another 5 x 7 = 35 to the total,
regardless of their orientation.
The die on the furthest left has
6 on top and 1 on the bottom, and
by comparing the orientation of
the 2 with that on the die at the
right, the furthest left die must
present a 4 to the adjoining cube.Hence the total of the touching
faces is: 5+35+4=44.Tom Gauld
for New Scientist
for its beautiful variegation.
We think the plant pictured is
Acalypha wilkesiana ‘Musaica’,
also known, appropriately,
as Jacob’s coat.
There are cultivars of this
plant with different shades of
green colours (due to the pigment
chlorophyll), and others that also
have red variegation (due to the
pigment anthocyanin). This
indicates that different genetic
processes are responsible for the
red and green colouration, which
is why they can occur together in
the same leaf.
Thinking about the greenish
sector first: white/pale green/
dark green variegation is quite
common in ornamental plants
and is seen most often when one
of the three layers of cells that
make up a leaf loses the ability
to make chlorophyll. However,
in the case of the plant in the
photograph, the irregular size
of the green/pale sections is
more reminiscent of the action
of a “jumping gene”, which is
a segment of DNA called a
transposable element.
If this element is inserted into a
gene required to make chlorophyll
or for chloroplast development,
this would result in white
“mutant” tissue. In parts of the
leaf where this element has been
excised, a mid-green colour is
produced. Other darker sectors
can also be seen where this
excision has occurred in two
overlapping layers of cells.
The leaf pictured also shows
variegation in its red anthocyanin
pigment (seen in the reddish
sections of the leaf). This
pigment absorbs excess light
and protects the photosynthetic
machinery of the leaf.
When the transposable element
is excised to give green sectors in
a leaf that is also producing red
anthocyanins, the sectors appeardarker due to the combination
of red and green.
As well as this variegation, the
leaf also seems to have a “twin
spot”, where in one sector of cells
all anthocyanin production has
been lost, and in the next sector
the cells are producing more
anthocyanin. This can be seen in
the left side of the leaf (pictured),
where one section looks black
and the one above it is pale.
Twin spots consist of two
genetically different clones
in a background of normal
cells. One explanation for the
anthocyanin twin spot in the
picture is that it resulted from
a process known as somatic
recombination, where daughter
cells are produced from cells
in the leaf with different
genes for the regulation of
anthocyanin production.
We have checked, and there
is very little literature available
on the variegation in Acalypha
wilkesiana. The advantage of
this lack of scientific investigation,
of course, is that we are free to
speculate on its causes! ❚