Cloning, Gene Therapy, and DNA Technologies

Cloning

• Cloning involves removing the nucleus of an unfertilized egg and replacing it with the nucleus of a body cell from the same species.
• The offspring will have the same number of chromosomes as the individual that donated the body cell.
• The egg is implanted into a female to develop, resulting in a clone.
• Cloning is used in agriculture to develop many of the foods we eat.
• Example: Cavendish banana is a clone of the original plant
• Cloning helps produce crops of consistent quality.
• Drawback: A population with little genetic diversity.

Gene Therapy in Humans

• Genetic diseases are caused by mutations in the DNA code.
• Mutations can be inherited or occur spontaneously.
• Gene therapy involves changing a gene to treat a medical disease or disorder.
• A normal working gene replaces an absent or faulty gene.
• One therapy involves genetically engineering immune-system cells and injecting them into a patient's body.
• Sickle Cell Disease:
  • Caused by a single mutation affecting hemoglobin.
  • Hemoglobin carries oxygen.
  • Mutation causes red blood cells to be shaped like a sickle or crescent.
• CRISPR:
  • Gene-editing tool for sickle cell disease.
  • Uses a guide RNA and an enzyme to cut out the DNA sequence causing the mutation.
  • Guide RNA takes the enzyme to the mutation.
  • Enzyme removes the sequence.
  • Another tool pastes a copy of the normal sequence into the DNA.

Practical Uses for DNA

• DNA sequencing: Determining the exact sequence of nitrogen bases in an organism's DNA.
• Human Genome Project:
  • Goal: Identify the sequence of the entire human genome.
  • The complete set of genetic information in an organism's DNA is the genome.
  • Completed in 2003.
  • Since sequencing the human genome, scientists research the functions of human genes.
  • Helps to better understand certain diseases, and how humans evolved.
• DNA technologies help diagnose genetic diseases.
• Genetic disorders result from mutations.
• DNA screening detects the presence of a mutation.
• DNA comparisons determine how closely related you are to another person.
• DNA fingerprint:
  • DNA is broken down into fragments.
  • Fragments are separated by size to produce a pattern.
  • Similarities between patterns determine who contributed the DNA.
  • Used to tie a person to a crime scene, prevent the wrong person from going to jail, identify remains, or identify the father of a child.

Artificial Selection

• Consumers are attracted to the best-tasting fruits and vegetables.
• Selective breeding (artificial selection) influences traits organisms inherit.
• Natural selection: Individuals with beneficial traits are more likely to survive and reproduce.
• Artificial selection: Humans breed organisms with desired traits to produce the next generation.
• Desired traits are not necessarily those that benefit the organism's survival.
• Dogs, cats, and livestock animals have been selectively bred.
• Cows, chickens, and pigs have been bred to be larger so that they produce more milk or meat.
• Animal husbandry: Breeding and caring for farm animals with desired genetic traits.

Genetic Engineering

• Genetic Engineering: Transferring a gene from the DNA of one organism into another.
• It is used to give organisms traits they could not acquire through breeding.
• Geneticists insert specific genes into animals.
• Scientists created a fish that glows under a black light by inserting a jellyfish gene for fluorescence into a fish egg.
• Genetic engineering is used to synthesize materials.
• Example: Insulin produced by genetically modified bacteria helps control blood-sugar levels.
• People who have diabetes cannot effectively control blood-sugar levels, and many must take insulin.
• Prior to 1980, some diabetics were injecting themselves with insulin from other animals without getting good results.
• Scientists genetically engineered bacteria to produce the first human protein (insulin).
• Bacteria reproduce quickly, so large quantities of insulin are produced in a short time.
• Process of bacteria producing human insulin:
  • Small rings of DNA, or plasmids, are found in some bacteria cells.
  • Scientists remove the plasmid and cut it open with an enzyme.
  • They then insert an insulin gene that has been removed from human DNA.
  • The human insulin gene attaches to the open ends of the plasmid to form a closed ring.
  • Some bacteria cells take up the plasmids that have the insulin gene.
  • When the cells reproduce, the new cells contain copies of the "engineered" plasmid. The foreign gene directs the cells to produce human insulin.