Goodbye Dolly

she is unforgettable, as both her birth and death stirred a raging debate. Dolly -- the first mammal to be cloned from an adult cell -- was put to death on February 14, 2003. The six-year old sheep was suffering from the fatal progressive lung disease.

Such a disease is common only in older sheep. Most sheep live for 11 or 12 years. A postmortem report would ascertain the cause of Dolly's disease.

Coming only a week after the death of the first sheep to be cloned in Australia, Dolly's demise is bound to raise fresh fears about the viability of cloning. The Australian sheep died unexpectedly on February 2, 2003, at the age of two years and 10 months.

Dolly -- a finn dorset sheep, named after the singer Dolly Parton -- was born on July 5, 1996 at the uk-based Roslin Institute. Dolly's birth raised hopes about human cloning. She bred normally on two occasions with a Welsh mountain ram called David. She first gave birth to Bonnie in April 1998, and then to three more lambs in 1999.

But in the same year, scientists noticed that the cells in Dolly's body -- cloned from the breast cell of a six year old ewe -- were showing signs of wear more typical of an older animal. Like some other cloned mammals, Dolly had shorter telomeres than other animals of her age. Telomeres are pieces of dna that protect the ends of chromosomes and research has shown that they act as molecular clocks, governing the process of ageing in the cells. In January 2002, she developed arthritis at an early. These findings indicated that researchers could not develop copies of animals without the original genetic blueprint wearing out quickly.

There are hundreds of animal clones across the world, including cows, pigs, mice and goats. Most are obese. Many attempts to clone animals have ended in failure, with deformed foetuses dying in the womb or having oversized organs. Such failures have raised ethical and scientific question about cloning, especially in the wake of human cloning.

genes and means

5000 BC: no corny origin
Humans discover that seeds produced by heartiest corn plants make the next crop strong. This is the first step towards manipulating life to suit human needs -- the ultimate goal of cloning

1952: tadpole leads
A tiny tadpole makes history as the first cloned animal. Using cells from a tadpole embryo, scientists create it

1972: xeroxing a gene
Scientists isolate a gene and then bind it to yeast. The organism incorporates the gene into its own DNA and multiplies, producing many copies of the gene

1987: cloned, not carboncopied
The first mammals -- sheep and cows -- cloned from embryonic cells. But they contain the genetic material of both parents

1996: hello, dolly
Dolly, world's first mammal to be cloned from the cell of an adult animal, is born

1998: mousetrapped
Scientists at the University of Hawaii clone more than 50 mice from adult cells. Other researchers successfully clone calves

2000: monkey business
US researchers reveal the existence of Tetra -- the 'so called' cloned monkey

2001: inhuman goal
US fertility specialist Panayiotis Zavos announces that hundreds of couples had volunteered for an experiment to create cloned children. Additionally, Britain legalises research on stem cells found in embryos

2002: just like mom
Texas A&M researchers clone a domestic cat. On December 26, 2002, the world's first cloned baby is born, claims Brigitte Boisselier. But she is unable to present a genetic match between mother and daughter

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