Polly and Molly facts for kids
Polly and Molly were two special sheep, born in 1997. They were the first mammals ever to be cloned from an adult cell AND have a new gene added to them at the same time. This made them "transgenic." They were different from Dolly the Sheep, who was also cloned from an adult cell but didn't have extra genes added. Like Dolly, Polly and Molly were created by scientists at the Roslin Institute in Edinburgh, Scotland.
Scientists created Polly and Molly using a method similar to how Dolly the Sheep was cloned. The main difference was that they put a new gene into the cells before cloning. This new gene was for a special protein that could help treat human diseases. The protein was human blood clotting factor IX. This showed how combining cloning with adding new genes could be very useful.
How Were Polly and Molly Made?
Before Polly and Molly, scientists usually added new genes to animals by injecting DNA into very early egg cells. But this method often did not work well. Only a few animals would get the new gene, and it might not work as expected. This made it a very expensive way to try and create animals with specific traits.
For mice, there was another way using special cells called "embryonic stem cells." These cells could be changed in a lab before making an animal. This allowed for more exact changes. However, scientists had not found similar stem cells for animals like sheep.
The cloning of Dolly the Sheep, and earlier sheep named Megan and Morag, showed that healthy sheep could be made by taking the nucleus from an adult cell and putting it into an empty egg cell. This process is called "nuclear transfer."
Polly and Molly were made using a similar nuclear transfer method. First, scientists took adult cells from a sheep. Then, they added a new, foreign gene to these cells. They carefully selected the cells that successfully took in this new gene. After that, they took the nucleus from these changed cells. They put this nucleus into an egg cell that had its own nucleus removed. This new cell then grew into an embryo, which was placed into a mother sheep. This process created several transgenic animals.
What is Factor IX?
The special gene added to Polly and Molly was designed to make human blood clotting factor IX protein in their milk. This protein is very important for blood to clot properly. People with a condition called haemophilia B do not have enough factor IX. They need to receive this protein through injections.
Making this protein in sheep's milk, a process called pharming, could provide a cheaper way to get this medicine. It would also be safer than getting it from human blood, which can sometimes carry infections.
See also
In Spanish: Oveja Polly para niños
