Implanted in uterus of a third sheep surrogate mother

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Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor 4 5 6 1 2 3 Cells fused Nucleus removed
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Figure 21.6 EXPERIMENT Researchers enucleated frog egg cells by exposing them to ultraviolet light, which destroyed the nucleus. Nuclei from cells of embryos up to the tadpole stage were transplanted into the enucleated egg cells. Frog embryo Frog egg cell Frog tadpole Less differ- entiated cell Donor nucleus trans- planted Enucleated egg cell Fully differ- entiated (intestinal) cell Donor nucleus trans- planted Most develop into tadpoles <2% develop into tadpoles Cloning
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Problems Most animals don’t develop normally Most have a short life health / social problems
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EXPERIMENT Transverse section of carrot root 2-mg fragments Fragments cul- tured in nutrient medium; stir- ring causes single cells to shear off into liquid. Single cells free in suspension begin to divide. Embryonic plant develops from a cultured single cell. Plantlet is cul- tured on agar medium. Later it is planted in soil. RESULTS A single Somatic (nonreproductive) carrot cell developed into a mature carrot plant. The new plant was a genetic duplicate(clone) of the parent plant. Adult plant CONCLUSION At least some differentiated (somatic) cells in plants are toipotent, able to reverse their differentiation and then give rise to all the cell types in a mature plant. Figure 21.5 Plants - Cloning Some differentiated cells are totipotent
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Stem Cells relatively unspecialized cell Can reproduces indefinitely Can differentiate into many types of specialized cells - given appropriate conditions
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Figure 21.4a, b Animal development. Most animals go through some variation of the blastula and gastrula stages. The blastula is a sphere of cells surrounding a fluid-filled cavity. The gastrula forms when a region of the blastula folds inward, creating a tube a rudimentary gut. Once the animal is mature, differentiation occurs in only a limited way for the replacement of damaged or lost cells. Plant development. In plants with seeds, a complete embryo develops within the seed. Morphogenesis, which involves cell division and cell wall expansion rather than cell or tissue movement, occurs throughout the plant’s lifetime. Apical meristems (purple) continuously arise and develop into the various plant organs as the plant grows to an indeterminate size. Zygote (fertilized egg) Eight cells Blastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell movement Gut Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical meristem Plant Embryo inside seed Two cells Zygote (fertilized egg) (a) (b)
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Stem Cells Pluripotent Can become several Types of cells Bone marrow Totipotent Can become Any cell Embryonic Figure 21.9 Early human embryo at blastocyst stage (mammalian equiva- lent of blastula) From bone marrow in this example Totipotent cells Pluripotent cells Cultured stem cells Different culture conditions Different types of
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