There are two main reasons. First, there are introns and exons existed in eukaryotes. Introns do not contain the genetic information but are in large amount in chromosome. So, if the mutation occurs in the introns, it will be recessive. Second, one amino acid will corresponding to several base sequences. For example, UUU and UUC all represent Phe. This is called degeneracy. So if the mutation did not change the amino acid, it is also recessive.
Stem cell therapies are not new. Doctors have been performing bone marrow stem cell transplants for decades. But when scientists learned how to remove stem cells from human embryos in 1998, both excitement and controversy ensued.
The excitement was due to the huge potential these cells have in curing human disease. The controversy centered on the moral implications of destroying human embryos. Political leaders began to debate over how to regulate and fund research involving human embryonic stem (hES) cells.
Newer breakthroughs may bring this debate to an end. In 2006 scientists learned how to stimulate a patient's own cells to behave like embryonic stem cells. These cells are reducing the need for human embryos in research and opening up exciting new possibilities for stem cell therapies.
The earth is cooled and its atmosphere is heated by terrestrial radiation.
