Dolly's Story: Cloning the First Mammal

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Dolly, a female Finn Dorset sheep, was born at the Scottish Roslin Institute in 1997.

• Why was her birth considered a scientific breakthrough?

Dolly was the very first clone of an adult mammal, ending the speculation that adult cells could not be genetically modified and used to create a clone.

Cloning Before Dolly

The idea of cloning is not new, and the process existed way before Dolly was born.

• So why did she create such a big buzz?

Before Dolly, laboratories had been producing natural clones similar to identical twins with the stem cells from a single zygote or fertilized egg. These mammals were clones of one another rather than clones from an adult.

Numerous attempts to clone from an adult failed. Scientists concluded it was too difficult to generate a new animal from just specialized adult cells -- like skin or brain cells.

(If you are unfamiliar with the differences between stem cells, check out our lesson under Additional Resources in the right-hand sidebar.)

Although birthing an entire new animal from a piece of skin had been successful in a few lower lifeforms like frogs, it had never been accomplished with a mammal -- until Dolly.

Making Dolly

Let's break down the process of cloning to make it a bit easier to understand.

Mammals reproduce when an egg is fertilized and becomes an embryo. The center of the unfertilized egg contains a nucleus with its genetic material.

Biologist Ian Wilmut and his team removed this nucleus from the egg. They then fused the egg cell with a cell they had taken from the mammary gland of an adult Finn Dorset ewe.

This fusion process resulted in the development of an embryo. The scientist created 13 of these embryos which they then placed inside 13 different surrogate Scottish Blackface ewes.

Only one out of those 13 ewes became pregnant. After 148 days, she gave birth. Welcome to the world, Dolly!

The technique used to produce Dolly is now known as somatic cell nuclear transfer (SCNT), and it has successfully cloned many other mammals since.

Watch the video below to see how this technique is accomplished.

Dolly's Life

As with any genetically modified organism, health issues were the primary concern for Dolly.

At the age of 1, her DNA analysis showed that she had shorter telomeres than other sheep her age. Telomeres are the ends of DNA, and they get shorter as mammals age. When DNA has short telomeres, it can be exposed to damages.

There were speculations that Dolly was suffering from accelerated aging because she came from an adult specialized cell; however, there was no indication to prove it.

Dolly was very popular and lived a normal life at the Roslin Institute. Over the years, Dolly had a total of six lambs with a Welsh Mountain ram named David. Their first lamb, Bonnie, was born in April 1998. Twins Sally and Rosie were born the following year, and triplets Lucy, Darcy, and Cotton the year after.

Last Years of Dolly

In the year 2000, Dolly and several other sheep at the Roslin Institute were infected with a virus called Jaagsiekte sheep retrovirus (JSRV), which causes lung cancer in sheep.

The following year, she developed a cough, and a CT scan showed tumors growing in her lungs. On February 14, 2003, the team at the Roslin Institute decided to euthanize her to avoid further suffering.

She was put to sleep at the age of six. Her body was donated and is currently on display at the National Museum of Scotland.

Watch the video below about Dolly.

There are many laboratories around the world that center their research on cloning in an attempt to find ways to improve human health; however, the federal government of the United States prohibits the practice of human cloning.

As this research becomes more sophisticated in the future, it will hopefully discover the answers to our outstanding medical mysteries!

Head over to the Got It? section to assess what you have learned so far.