Chapter 16 : Biotechnology in the Research Laboratory

Isolating E. coli mutants that cannot biosynthesize histidine (His−).

Using an E. coli mutant to find an E. coli gene.

Analysis of the DNA of genetically obese mice led scientists to genes involved in weight regulation. (Photograph courtesy of Jeffrey Friedman, The Rockefeller Institute.)

Purebred dogs are an excellent resource for scientists curious about the genetic basis of many different traits. Scientists in Mexico are analyzing the DNA of short legged breeds such as the basset hound to determine the molecular basis of their dwarfism. The DNA profile of this basset hound, Champion Rebec's Fuzzy Navel, ROM (aka Fuzzy), is on file with the American Kennel Club. (Photograph courtesy of Reed and Becky Pomeroy, Rebec Bassets.)

Genetic testing for SSA. bp, base pairs.

The breeding of drought-resistant rice for use in eastern India was facilitated by genetic markers. Rice is a staple crop for billions of people in developed and less-developed countries. (Photograph courtesy of the U.S. Department of Agriculture.)

Madagascar is a large island off the east coast of Africa.

The falanouc is one of Madagascar's unique carnivores. (Photograph courtesy of the Field Museum, Chicago, Ill., #CSZ77048.)

Gene sequence comparisons revealed that Madagascar’s carnivores descended from one common ancestor whose closest living relative is the mongoose. (Diagram courtesy of John Flynn, Marlene Donnelly, and Anne Yoder, the Field Museum, Chicago, Ill.)

Mitochondrial DNA. kb, kilobases.

Inheritance of mitochondrial DNA is matrilineal. That is, the mitochondrial genotype (symbolized here by the colors in the male and female symbols) is inherited from the mother. Note that all family members related through the female line share the same mitochondrial genotype.

Evolutionary tree based on the amino acid sequence of the protein cytochrome c. The numbers represent the number of amino acid changes between two nodes of the tree. For example, when the common ancestor of cartilaginous fish diverged from the line leading to bony fish, mammals, etc., it evolved and accumulated two amino acid changes in its cytochrome c protein before the lines leading to dogfish and lamprey diverged. The dogfish line accumulated nine more amino acid changes in becoming the modern organism, while the lamprey accumulated eight changes. Thus, the amino acid sequences of cytochrome c in modern lampreys and dogfish have 17 differences. (From A. Lehninger, D. Nelson, and M. Cox, Principles of Biochemistry, 2nd ed., Worth Publishers, Inc., New York, N.Y., 1993, with permission.)

Scientists obtain information about evolutionary changes by analyzing DNA from ancient specimens, such as insects trapped in amber. This insect is a timber beetle. (Photograph courtesy of Fossilmall.com.)

Neanderthals (skull cast on right), with their large brains and anatomy similar to ours, were long believed to be direct ancestors of modern humans (skull model on left).Mitochondrial DNA analysis suggests that modern humans instead arose independently of Neanderthals and displaced them. (Photograph courtesy of SOMSO Models, Coburg, Germany.)

RFLP analysis. L, ladder; E, evidence; S1, suspect 1; S2, suspect 2.

Variation in the numbers of tandem (head-to-tail) repeated sequences at many different locations within the genome provides a basis for genetic fingerprinting. To generate a fingerprint, laboratory technicians amplify many different loci using a specific set of primers for each one, or they digest the sample DNA with restriction enzymes known to cut at sites flanking the repeats.

Parentage testing by DNA typing. To conduct a test, the DNA fingerprints of the child and the alleged parent are compared. Every band in the child's fingerprint should be present in that of either the mother or father, since a child inherits half its DNA from each parent.

Lions are the only cats who live in large social groups, or prides. A pride is made up of 3 to 30 lions, consisting of related adult females and their cubs along with a few males who are not related to the females. DNA typing is revealing new information about social behavior and genetic variation in lions. (Photograph courtesy of the St. Louis Zoo.)

This handheld device contains a gene chip with thousands of probes. (Photograph courtesy of Affymetrix, Inc.)

DNA chips can reveal an individual's genotype by hybridizing his or her DNA to probes specific to the known alleles of the gene.

A developed gene chip must be read by computerized sensors. (Photograph courtesy of Affymetrix, Inc.)

Genes are often cloned so that their expression can be controlled. For example, a gene cloned with the lac promoter will be expressed only if lactose is present in the growth medium.

Plant tissue culture. (A) Pieces of plant tissue can be induced to form undifferentiated callus cells (plates on right). Manipulation of hormones in the growth medium causes the callus to differentiate into tiny plantlets (plates on left). (B) Close-up of plantlet. Note the fuzzy roots and tiny leaves. (Photographs courtesy of Syngenta.)

A stand of transgenic PRSV-resistant papaya plants surrounded by PRSV-sensitive plants that have been ravaged by the virus. (Photograph courtesy of Dennis Gonsalves, USDA.)

Researchers at Virginia Tech produced transgenic pigs that secrete human blood-clotting proteins in their milk. Hemophilia patients can be treated with the purified clotting factors without incurring the risk of infection posed by multiple transfusions of human blood. (Photograph courtesy of Virginia Tech Photo.)

Making a transgenic mouse with ES cells.

Chimeric mice produced via the fusion of ES cells and a blastocyst. The white fur is derived from blastocyst cells, while the brown fur is derived from the ES cells. (Photograph courtesy of Murinus GmbH, Hamburg, Germany.)

RNAi.In RNAi, dsRNA homologous to the RNA of the gene to be silenced is used. The cellular enzyme Dicer cleaves the dsRNA into short siRNAs. A second cellular protein uses homology between the siRNA and the target mRNA to locate the target by hybridization and then cleave it.