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child. Two, the amount of DNA carried in
the mitochondria – just 37 genes in total,
compared to 20,000 in the nucleus – is
tiny, a mere 0.1 per cent of the entire
genome.
And three, children have already been
born who carry DNA from three parents.
Women who act as surrogate mothers
have been found to pass minute amounts
of mitochondrial DNA to the babies they
carry for nine months. Meanwhile, in the
late 1990s, children conceived through
‘ooplasmic transfer’ – an IVF technique
used to bolster the viability of eggs by
injecting cytoplasm from young donor
eggs into the older eggs of women
undergoing fertility treatment – were later
found to carry small amounts of DNA
from the donor. Some of the resulting
children are alive and well. The US Food
and Drug Administration (FDA),
however, put the brakes on this treatment
back in 2001, and has yet to approve the
new mitochondrial donation technique.
Yet mitochondrial donation is distinct
from surrogacy and cytoplasmic transfer
for one simple reason: it is overtly
intended to create children with DNA
from three parents. Thus there is
something inherently more unsettling

about deliberately seeking to alter the

inheritable DNA of a child. Unlike a

course of drug treatment, genetic changes

are permanent. The New York Times

called the creation of “genetically

modified babies” (an undeniably emotive

descriptor) “a dangerous step” and an

“extreme procedure” in a 2014 opinion

piece by Marcy Darnovsky, Executive

Director of the Center for Genetics and

Society. Naturally, this led to fears that

mitochondrial donation could lead to

‘designer babies’ (despite the fact that

mitochondrial genes do not code for

visible traits such as eye colour). A

Republican representative for Nebraska,

Jeff Fortenberry, went so far as to call it “a

macabre form of eugenic cloning”.

Knee-jerk reactions aside, there are

reasons to be cautious. Research is

increasingly revealing that mitochondria

are far more important than mere

‘batteries’, and have duties that

include inf luencing the speed of

HOW IT

WORKS:

There are several

techniques for creating a

baby from three parents

Here are two of them...

SPINDLE

TRANSFER

1. Start with two
   eggs – one from
   a mum-to-be
   with diseased
   mitochondria, one
   from a donor with
   healthy mitochondria.
   Remove nuclear DNA
   from both eggs.
   2. Transfer nuclear DNA
   from the mother’s egg
   into the donor egg, which
   contains only healthy
   mitochondria but no
   nuclear DNA. Discard
   remainder of mother’s egg.
   3. Fertilise the complete egg – now
   containing the mum’s nuclear DNA –
   with the father’s sperm. Allow to develop
   into an embryo.
   4. Implant the embryo, now containing
   donor mitochondria, and DNA from both
   the mum and the dad – three parents in
   total – into the mother’s womb.

Donor

egg

Nuclear DNA

discarded Remainder

of egg

containing

mtDNA

(mtDNA)

Reconstructed egg

with healthy mtDNA

fertilised

Patient’s

egg

with

faulty

mtDNA

Embryo

implanted

into patient

Rest of egg

discarded

Nuclear DNA

transferred to

donor egg

mtDNA = mitochondrial DNA 3.