Cloning of a Human

Jenna Mendenhall

Cloning humans

Scientists generate clones by replacing the nucleus of an egg cell with that from another individual. They have cloned human embryos, but none has yet successfully grown past the early stage where they are solid balls of cells known as morals. The act of transferring the nucleus may disrupt the ability of chromosomes to align properly during cell division. "Whenever you clone a new species, there's a learning curve, and with humans it's a serious challenge getting enough good-quality egg cells to learn with," says Robert Lanza of Advanced Cell Technology in Worcester, Mass., who made headlines in 2001 for first human embryos. Especially tricky steps include discovering the correct timing and mix of chemicals to properly reprogram the cell.

Cloning animals

Animal cloning

Cloning gives a farmer complete control over an offspring's inherited traits, overcoming the unpredictability of conventional forms of breeding. Through cloning, breeders can produce multiple genetic copies of the best animals in the herd--those with naturally occurring desirable traits, such as disease resistance or quality meat production, and introduce these traits into production herds more rapidly than with sexual reproduction.