Genetic Engineering and Selective Breeding Techniques
DNA Polymerase: Sequencing vs. Cellular Function
Contrast the role of DNA polymerase in determining a DNA sequence with its role in normal cells.
In DNA sequencing, DNA polymerase replicates small pieces of DNA using normal bases and some bases that are tagged with dye. Each base can be tagged with a different color dye. The dye-tagged bases stop replication. After running the bases on a gel, scientists can determine the sequence of the DNA by reading the order of the colored bands on the gel. In normal cells, DNA polymerase builds new DNA strands based on the parent strands but does not use bases that have been tagged with dye.
Chromosome Size and Gene Count: A Misconception
Why might it be incorrect to assume that if one chromosome is larger than another, the larger chromosome has more genes?
The larger chromosome might be larger because it has longer stretches of repetitive DNA than the smaller chromosome. Because repetitive DNA does not code for proteins, it does not contain genes. Thus, in this case, the larger chromosome does not have more genes than the smaller chromosome.
Inbreeding: Advantages and Disadvantages
Explain an advantage and a disadvantage of inbreeding.
Examples will vary. The advantage of inbreeding is that it maintains desired traits within a breed, such as curly hair in poodles. The disadvantage is that it can lead to genetic defects within a breed because of the likelihood that an individual could inherit two defective, recessive alleles.
Selective Breeding: Creating Organisms with Desired Traits
Suppose you want to produce a new animal breed or plant species with certain desirable traits. Write a brief description of the traits you would want the organism to have. Then, explain how you would use selective breeding techniques to produce an organism with those traits.
Answers will vary. Students should include in their answers the traits that they will select for and the methods that they will use to select for those traits, such as hybridization and inducing mutations.
Genetic Engineering for Enzyme Production
Suppose you are a scientist trying to help people who cannot produce an enzyme needed for proper digestion. How could you use genetic engineering techniques to make transformed bacteria that produce the enzyme?
- Extract DNA from the cells of people who can make the digestion enzyme.
- Cut the DNA with a restriction enzyme, then use gel electrophoresis and a DNA probe to locate the gene.
- Use the polymerase chain reaction to copy the gene.
- Choose a plasmid that has an antibiotic-resistance genetic marker, and cut the plasmid with the same restriction enzyme used to cut out the human gene.
- Insert the copies of the human gene into the plasmids.
- Allow bacterial cells to take in the plasmids.
- Select for transformed bacteria by growing them in a culture containing the antibiotic.
These bacteria will make the digestion enzyme.
Genetic Engineering vs. Selective Breeding
Compare and contrast the techniques used in genetic engineering and in selective breeding to produce organisms with desired traits.
In genetic engineering, organisms with desired traits are produced by directly changing the DNA of the organisms. This is done by cutting out desirable genes from the DNA of certain organisms and inserting them into the DNA of other organisms. In selective breeding, organisms with desired traits are produced by selecting organisms for their traits and then mating, or crossing, them. Selective breeding does not directly change the DNA of living organisms.