One very important point to remember is that knowing the sequence of a genome is not the same as actually having that sequence made up and viable in front of you.   

Let us imagine that we have, astonishingly, overcome all hurdles and have engineered a complete and viable strand of dinosaur DNA – let’s choose a complete strand of Sinosauropteryx which lived 130 – 145 million years ago, which puts it nicely in the late Jurassic.  In the film, the scientists then cloned the dinosaur.  Cloning is the process of making a genetically identical organism through non-sexual means.  It has been used for years – even taking a cutting from a plant is cloning.  Identical twins are clones.

 

Cloning relies on taking a DNA from a normal cell with the full complement of chromosomes, and then the process of cell division by mitosis copies this DNA exactly. 

Currently, cloning animals relies on nuclear transfer – the transfer of the nucleus from one cell into an oocyte (an unfertilized cell from an ovary).  The first nuclear transfer was carried out in 1952, with the source of nuclei being a very early embryo (baby) of the frog Rana pipens.

 

In the 1970’s the scientist John Gurdon successfully cloned tadpoles using the nucleus from a specialised

frog cell. Click on the frog on the right to go to download an image of how he did it.  This was very important

– it demonstrated that it was no longer necessary to take nuclei from an embryo, and that the process of

specialisation in animal cells is reversible:  the DNA from a specialised skin cell was able to create an

entire new organism.

                                           In 1996, the first successfully cloned mammal, Dolly the sheep, was created, again using nuclear                                             transfer.

 

                                           However, with all three of the examples above, there is one outstanding and vital fact:  the oocyte                                              has come from the same species as the nuclear DNA.  In our case, this would be a dinosaur.                                                   Since no dinosaurs are alive today, we cannot obtain a dinosaur donor egg cell.

                                             It wouldn't work to insert the DNA into crocodile oocyte (as suggested in the film), because                                                      crocodile oocyte is specialied for crocodiles, not dinosaurs.  The reason for this is that                                                              development of an embryo is an incredibly sensitive process, even in naturally occurring                                                            fertilisation. When an embryo initially begins to divide, proteins present in the egg are responsible                                              for ensuring that cell division occurs properly, and that those cells begin to express the correct                                                  genes at the correct times. 

 

Even if crocodile ova could hold dinosaur DNA, a problem still arises with the development of the dinosaur embryo.

 

 

As development continues, cells must differentiate; change from being a general cell to a specific tissue that only expresses a small number of the genes present in the nucleus.  Remember the experiments of John Gurdon that demonstrated that each adult cell still contains that necessary information to create an entire organism.  Differentiation happens early on and is stimulated by signals already present inside the original oocyte.  Proteins in the oocyte must recognise specific sequences found in the DNA of the nucleus.  In the case of cloning the DNA inserted into the oocyte must come from the same, or a very closely related species, or the DNA and proteins will not recognise each other.  Imagine, if you like, that the oocyte speaks only ancient Greek and the inserted nucleus speaks only Japanese.  There is no way that the two can communicate with each other to build the IKEA flat-pack furniture.

 

In addition, there is a second set of DNA inside the oocyte, called mitochondrial DNA.  This is

always inherited from the mother and contains the genes involved in creating energy for the cell.

  Mitochondrial DNA must also match the species from which the nucleus comes, or the cell will

have difficulties creating energy.  Without energy the cell cannot survive.

 

Cloning mammals is fraught with difficulty.  For every 500 somatic cell nuclear transfers only one

is likely to create an embryo.  In 1996, Ian Wilmut and his colleagues – who created Dolly the

Sheep - had to generate98 embryos, to get 16 that were able to divide into a multi-cellular embryo.

  Of these only 8developed into foetuses, and only one (Dolly) survived more than a few days after

being born. 

 

It has proved even harder to clone extinct animals.  The last Bucardo or Pyrenean ibex died in

1999, crushed beneath a fallen tree.  However, the cells of this Burcardo, whose name was

Celia, were preserved in a laboratory in Madrid.  Over the next few years attempts were made

to create a Burcardo clone, using purely Burcardo egg and nucleus but carried within a goat– the

closest relative they could find.  57 Embryos were implanted in 57 goats.  Only 7 of those goats

became pregnant.  Of those seven, six miscarried and one carried the Burcardo clone to term. 

The clone was born, on 30 July 2003, by caesarean section, but died within 10 minutes, unable

to breathe.  A necropsy revealed that the lungs had grown a gigantic extra lobe as solid as a

piece ofliver.  This simply demonstrates how spectacularly difficult it is to clone an animal with

success.

 

We all know, however, that dinosaurs were reptilian – they hatched from eggs.  Therefore, there

would be no need for implantation and pregnancy.  Instead, however, the embryo would need to be

placed inside an egg.  In the film, embryos were placed in plastic eggs, and incubated with 100% humidity and at 37 degrees C.  The ‘eggs’ then hatched naturally and baby dinosaurs emerged.  The difficulty here is that, in reality, even a fertilised hen’s egg spends a few days in the mother hen’s oviduct before being laid, and it is thought that certain vital developments take place there.  For a dinosaur, we would need to find a suitable egg-laying host that was sufficiently large enough itself to carry the large egg needed to ‘grow’ a dinosaur.