Biotechnology

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11

EXPERIMENT

Less differ- entiated cell

RESULTS

Frog embryo

Frog egg cell

UV

Donor nucleus trans- planted

Frog tadpole

Enucleated

egg cell

Egg with donor nucleus

activated to begin

development

Fully differ-

entiated

(intestinal) cell

Donor

nucleus

trans-

planted

Most develop

into tadpoles

Most stop developing

before tadpole stage

Slide 78

Reproductive Cloning of Mammals

In 1997, Scottish researchers announced the birth of Dolly, a lamb cloned from an adult sheep by nuclear transplantation from a differentiated mammary cell

Dolly’s premature death in 2003, as well as her arthritis, led to speculation that her cells were not as healthy as those of a normal sheep, possibly reflecting incomplete reprogramming of the original transplanted nucleus

Slide 79

Fig. 20-18

TECHNIQUE

Mammary cell donor

RESULTS

Surrogate mother

Nucleus from mammary cell

Cultured mammary cells

Implanted in uterus of a third sheep

Early embryo

Nucleus removed

Egg cell donor

Embryonic development

Lamb (“Dolly”) genetically identical to mammary cell donor

Egg cell from ovary

Cells fused

Grown in culture

1

3

3

4

5

6

2

Slide 80

Since 1997, cloning has been demonstrated in many mammals, including mice, cats, cows, horses, mules, pigs, and dogs

CC (for Carbon Copy) was the first cat cloned; however, CC differed somewhat from her female “parent”

Slide 81

Fig. 20-19

Slide 82

Problems Associated with Animal Cloning

In most nuclear transplantation studies, only a small percentage of cloned embryos have developed normally to birth

Many epigenetic changes, such as acetylation of histones or methylation of DNA, must be reversed in the nucleus from a donor animal in order for genes to be expressed or repressed appropriately for early stages of development

Slide 83

Stem Cells of Animals

A stem cell is a relatively unspecialized cell that can reproduce itself indefinitely and differentiate into specialized cells of one or more types

Stem cells isolated from early embryos at the blastocyst stage are called embryonic stem cells; these are able to differentiate into all cell types

The adult body also has stem cells, which replace nonreproducing specialized cells

Slide 84