Slide 13 of 63

Cloning of non-mammals was first accomplished in 1952. However, cloning of mammals proved much more difficult, with the first successful clone being the sheep, Dolly. Dolly died a premature death, probably due to the use of aged Threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.chromosomes in her nuclear transfer. Other mammal species followed rapidly, with mice and cows being cloned in 1998, and pigs in 2000.