Cloning? Just a simple CtrlC CtrlV?

How does animal cloning exactly work?

Cloning is always a point of debate whether the points made are even relevant or not. Some people will always be dismissing it as wrong or dangerous as long as they do not understand it. Thus I decided to write a short piece about how cloning works. Including a few extra facts and some misconceptions.

How does cloning work?

The point of cloning is to start a zygote (=a fertilized egg cell) but in this zygote you want the same genetic material as the organism you want to clone. The easiest way is to take the nucleus from a somatic(=body) cell, which often are the skin or liver cells. All the cells in an organism have the same set of DNA in the nucleus. For cloning you can take an egg cell that has been naturally ovulated and remove the egg cell nucleus containing the unwanted DNA. After this you just replace the nucleus, by putting the somatic nucleus in the ’empty'(=enucleated) egg cell. Now we need to wait a few hours to let the DNA ‘rearrange’ itself for this new cell. When this ‘rearranging’ has been done, mitosis(=cell division) can be induced. After this ‘fertilization’ you can put it in a surrogate mother and it will grow just like a normal fertilized egg cell.

The famous Dolly

The famous Dolly experiment

What animals have been cloned so far?

Since the famous Dolly experiment a number of mammals have been cloned including cats, cattle, deer, dogs, ferrets, goats, gaurs, horses, cows, mice, mouflons, mules, pigs, rabbits, rats, rhesus monkeys, sheep, water buffalo and wolves. One of these animals is CC. A cloned cat, “Operation CopyCat”, which was part of a bigger research to clone the dog “Missy”, “Operation Missyplicity”.

Do you get exact carbon copies when cloning an animal?

When CC was born one things was apparent, her DNA was the same of that as her ‘mother’s’ Rainbow, but their calico pattern was different. Although this has nothing to do with CC being a cloned cat, it does give an idea of the problems of cloning animals for ‘commercial’ ends. This different calico pattern is caused by X-inactivation, also called Lyon-hypothesis after it’s discoverers Marie Lyon and Lillian Russell (1961). Because it is a female cat it has two X chromosomes. To prevent females from having more active X-chromosomes than men do one gets ‘inactivated’. The fun thing is, is that the gene encoding the colour of the fur is on this chromosome. When the cells divide, at some point the cell turns off one of its 2 X-chromosomes and all ‘offspring’ of this cell have the same chromosome in its off-setting. So if one cell turns of X-chromosome-I, encoding a black colour, the resulting colour is orange. If it would turn off X-chromosome-II, encoding an orange colour, the resulting colour would be black. This is what results in the patchy colours of the fur.

Rainbow, the donor on the left. Copycat and surrogate mother on the right.

Rainbow, the donor, on the left. Copycat and surrogate mother on the right.

Why don’t we make an army of the clones?!

Since many clones die before and only moments after birth, it suggests the survivors have something special. For example changes in gene regulation. Experiments done by Rudolph Jaenisch at the Whitehead Institute for Biomedical Research found that clones and cultured cells that have a donor nucleus have changes in gene expression that allows them to survive the transposition from cell A to cell B. This could mean that the clones that survive have unforeseen problems with health and are unlikely to be ‘normal’.

Another problem is that the cells that you take the nucleus from are often already differentiated (=taken on a certain task, in which process they ‘turn off’ some parts of the DNA). If you take this differentiated nucleus and transfer them into another cell, it will probably cause problems because it’s hard for a nucleus to redifferentiate.

Because of all these issues and lack of tools to fix these problems, human cloning is of course out of the question.

Nothing like this anytime soon.

Nothing like this anytime soon.


Clones born do not have the same age as the ‘parental donor’. They are born like any other animal. They are born babies and age normally.

Clones do not possess the same memory or recollection as the parental donor. It’s a different organism, just the same DNA.

Clones do not look exactly like the parental donor, environment is a very important factor in the phenotype(=all expressed traits etc.) of an organism.

Cloning is not per definition unnatural, many plants, bacteria, fungi and some animals clone themselves.


p 348-349, ‘Chromosomal Basis of Inheritance’ p 550-552‘Genetic Analysis of Development’ iGenetics 3rd edition – by Peter J. Russell

Wikipedia Cloning entry

Learn.Geneticstm Utah University Genetic Learning Centre.


“The Dolly Experiment”

from Cloning via

Microinjection picture from:

Les protocoles de stimulation oarienne en vue de fecondation in vitro : evolution au cours de dernieres ann. Médecine Thérapeutique Endocrinologie & Reproduction. Volume 5, Number 1, 7-17, Janvier 2003, Fécondation in vitro

Hugues et al. , Service de Médecine de la Reproduction, Hôpital Jean‐Verdier, AP‐HP, Av du 14 Juillet, 93143 Bondy, France .

Copycat image from James Meek, science correspondent The Guardian, Friday 15 February 2002 17.09 GMT – “First cloned kitten – but it’s not an exact copycat”


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