Biotechnology

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Rinse off excess cDNA; scan microarray for fluorescence. Each fluorescent spot represents a gene expressed in the tissue sample.

Tissue sample

mRNA molecules

Labeled cDNA molecules (single strands)

DNA fragments representing specific genes

DNA microarray with 2,400 human genes

DNA microarray

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Slide 71

Determining Gene Function

One way to determine function is to disable the gene and observe the consequences

Using in vitro mutagenesis, mutations are introduced into a cloned gene, altering or destroying its function

When the mutated gene is returned to the cell, the normal gene’s function might be determined by examining the mutant’s phenotype

Slide 72

Gene expression can also be silenced using RNA interference (RNAi)

Synthetic double-stranded RNA molecules matching the sequence of a particular gene are used to break down or block the gene’s mRNA

Slide 73

Organismal cloning produces one or more organisms genetically identical to the “parent” that donated the single cell

Concept 20.3: Cloning organisms may lead to production of stem cells for research and other applications

Slide 74

Cloning Plants: Single-Cell Cultures

One experimental approach for testing genomic equivalence is to see whether a differentiated cell can generate a whole organism

A totipotent cell is one that can generate a complete new organism

Slide 75

Fig. 20-16

EXPERIMENT

Transverse section of carrot root

2-mg fragments

Fragments were cultured in nu- trient medium; stirring caused single cells to shear off into the liquid.

Single cells free in suspension began to divide.

Embryonic plant developed from a cultured single cell.

Plantlet was cultured on agar medium.

Later it was planted in soil.

A single somatic carrot cell developed into a mature carrot plant.

RESULTS

Slide 76

Cloning Animals: Nuclear Transplantation

In nuclear transplantation, the nucleus of an unfertilized egg cell or zygote is replaced with the nucleus of a differentiated cell

Experiments with frog embryos have shown that a transplanted nucleus can often support normal development of the egg

However, the older the donor nucleus, the lower the percentage of normally developing tadpoles

Slide 77

Fig. 20-17