The British government proposes to ban the creation of hybrid human-animal embryos that scientists hope to use to find treatments for degenerative disorders such as Alzheimer's disease.

Creating the hybrids, called chimeras, involves taking human DNA from the skin cells of people suffering from the diseases and placing it in an animal egg. 

The resulting embryo is 99.5 per cent human, giving scientists a source of stem cells for research. There is a shortage of human eggs for researchers to work with in Britain.

The nucleus of the animal embryo is removed from the egg, making it little more than a shell, scientists say.

Cells are harvested after six days and the embryo is destroyed after two weeks. The mixed embryos are not permitted to grow to maturity.

Human-animal hybrids are already outlawed in Canada under the Assisted Human Reproduction Act, and the British government is proposing similar legislation within a year.

Consultations in Britain showed widespread discomfort among the public with the idea of chimeras. People said they were horrified by images of mice with human ears growing on their backs and pigs bred with human blood running through their veins.

Researchers say the concept of chimeras is misunderstood and stress that the embryos would never be allowed to mature.

Scientists hope that studies on stem cells — immature cells that have the ability to become many types of tissues — could lead to better understanding of and treatment for diseases such as Alzheimer's and Parkinson's.

Britain's Human Fertilisation and Embryology Authority, or HFEA, will make a policy decision on the licensing of human-animal embryo research on Jan. 10, according to the body's website.