BBC_Knowledge_Asia_Edition_-_May_2016_

Could two people

who aren’t twins have

the same DNA?

As a species, humans actually show remarkably little ge

diversity. The DNA of two unrelated people only differs y

about one in every 1,000 base pairs; orangutans differ b

more than double this amount. Even so, there are three

billion base pairs in the human genome, so that’s an

average of three million genetic differences between

any two strangers. Most of these differences are

‘single nucleotide polymorphisms’ (SNPs), in which

a single letter of the genetic code is changed. There

are about 20 million known SNPs in the human

genome. This means that the odds of someone

having the same DNA by chance is like having a deck

of 20 million cards, all different, and then drawing the

same hand of three million cards twice! LV

QUESTION OF THE MONTH

c i i

a i i

c i

Could we genetically engineer

animals to be photosynthetic?

There isn’t a single gene
for photosynthesis, which
is the process plants use
to produce glucose from
the Sun’s energy. Plants
can photosynthesise
because their cells contain
chloroplasts, which
were originally free-living
bacteria that entered into a
symbiotic relationship with
single-celled organisms
about 1.5 billion years
ago. Chloroplasts have
their own DNA and
reproduce inside plant
cells, but they also need
the plant to provide the
right environment.
In 2010, Harvard
researchers tried injecting
photosynthetic bacteria
into the eggs of zebrafish.

They found that the

bacteria were still alive

two weeks after the fish

hatched. But the bacteria

didn’t grow or reproduce

and they didn’t generate

much sugar.

Some animals in nature

have partially harnessed

photosynthesis. For

example, reef-building

corals and giant clams

contain photosynthetic

algae. But photosynthesis

only creates sugar. Plants

can make all the other

biochemical molecules

they need, but animals

must absorb additional

nutrients from food, so

photosynthesis could

never be a complete

replacement for eating. LV

enetic

by

by

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Most reef-building corals

contain photosynthetic

algae, whichprovide the

corals with glucose