Chapter 13 Genetic Technology
Selective Breeding • For a long time, humans have selected the best plants and animals to breed • Why? • Examples? • Milk Cows • 1947 - produced 4,997 lbs... of milk/year • 1997 - produced 16,915 lbs.... of milk/year • Increasing the frequency of desired alleles in a population is the essence of genetic technology
Inbreeding • Mating between closely related individuals • Why? • Done to make sure that breeds consistently exhibit a trait and to eliminate undesired trait • Creates purebred lines • Can be bad also • Can bring out harmful, recessive alleles in a “family”
Hybrids • It can be beneficial to create hybrids • For example, disease-resistant plants crossed with plants that produce bigger fruit • Offspring get both qualities • Hybrids produced by crossing two purebred plants are often larger and stronger than their parents
Test Crosses • A test cross is a cross of an individual of unknown genotype with an individual of known genotype (usually homozygous recessive) • How will this work? • Results when heterozygous x homozygous? • Results when homozygous x homozygous? • When is this practical?
Section 1 Review • A test cross made with a cat that may be heterozygous for a recessive trait produces ten kittens, none of which has the trait. What is the presumed genotype of the cat? Explain. • Suppose you want to produce a plant that has red flowers and speckled leaves. You have two offspring, each having one of the desired traits. How would you proceed? • Why is inbreeding rarely a problem among animals in the wild? • Hybrid corn is produced that is resistant to bacterial infection and is highly productive. What might have been the phenotypes of its two parents? • How is selective breeding done? • What effect might selective breeding of plants and animals have on the size of Earth’s human population? Why?
Genetic Engineering • Selective breeding may take a while to produce a purebred “line” • Genetic engineering is a faster and more reliable method for increasing the frequency of an allele in a population • This involves cutting - or cleaving - DNA from one organism into small fragments and inserting the fragments into a host organism of the same or a different species • Also called recombinant DNA technology. • Connecting, or recombining, fragment of DNA from different sources
Transgenic Organisms • Plants and animals that contain functional recombinant DNA from an organism of a different genus • Ex: they grow a tobacco plant that glows from a gene in a firefly • 3 steps: • Isolate the foreign DNA fragment to be inserted • Attach the DNA fragment to the carrier • Transfer the DNA into the host organism
Restriction Enzymes • Bacterial proteins that have the ability to cut both strands of the DNA molecule at a specific nucleotide sequence • Some enzymes cut straight across • Called blunt ends
Restriction Enzymes • Many enzyme cut in palindromes • Ex: a protein only cuts at AATT, it will cut the two fragments at different points - not across from each other (called sticky ends) • Called sticky ends because they want to bond with things due to their “open” end • These sticky ends are beneficial, because if the same enzyme is used in both organisms, they will have identical ends and will bond with each other
Vectors • DNA fragments don’t just attach themselves to another fragment, they need a carrier • A vector is the means by which DNA from another species can be carried into the host cell • Vectors may be biological or mechanical • Biological vectors include viruses and plasmids • A plasmid is a small ring of DNA found in a bacterial cell • Mechanical vectors include micropipettes and a little metal bullet coated with DNA shot with a gene gun into a cell
Insertion Into a Vector • If the plasmid and the DNA fragment were both cleaved with the same enzyme, they will stick together because they have “sticky ends” • A second enzyme helps this process
Labs • Mini-Lab 13.1 • Page 343 • Modeling Recombinant DNA • Page 354
Gene Cloning • Once the fragment is in the plasmid, the bacterial makes many copies of the DNA • Up to 500 copies per cell • Clones are genetically identical copies • Each copied recombinant DNA molecule is a clone • If the plasmid is placed into a plant or animal cell, the cell reproduces that DNA also and makes those proteins coded for
Cloning Animals • Dolly was the first animal cloned in 1997 • Since then, goats, mice, cattle, pigs, etc. have been cloned • Take DNA out of embryonic stem cells or zygote and insert new DNA
Polymerase Chain Reaction • A way to artificially replicate DNA • DNA is heated and the strands separate • An enzyme isolated from a heat-loving bacterium is used to replicate the DNA when nucleotides are added (in a thermocycler) • Makes millions of copies in less than a day • Why could this be helpful?
Sequencing DNA • First, PCR is done to make millions of copies • Separate the strands of DNA • Place in four different tubes with four different restriction enzymes that cut at one of the four bases (A,T,C,G) • A fluorescent tag is also placed at each cut • The fragments are separated according to size by a process called gel electrophoresis • Produces a pattern of fluorescent bands in the gel • Shows the sequence of DNA
Gel Electrophoresis • The gel is like firm gelatin • Molded with small wells at one end • Has small holes in the gel (not visible) • DNA has a slight negative charge • A current is run through the gel and an added buffer fluid • DNA will move towards the positive end • Smaller fragments fit through the holes in the gel better and move farther
Gel Electrophoresis gslc
Recombinant DNA in Industry • E. coli has been modified to produce an indigo dye to color blue jeans • Recombinant DNA has been used to help production of cheese, laundry detergent, paper production, sewage treatment • Increase enzyme activity, stability and specificity
Recombinant DNA in Medicine • Production of Human Growth Hormone to treat pituitary dwarfism • Insulin Production by bacterial plasmids • Antibodies, hormones, vaccines, enzymes, and hopefully more in the future
Transgenic Animals • Mice reproduce quickly and have chromosomes that are similar to humans’ • The genome is known better • The roundworm Caenorhabditis elegans and the fruit fly, Drosophila melanogaster are also well understood • Used in transgenic studies
Transgenic Animals • A transgenic sheep was produced that contained the corrected human gene for hemophilia • This human gene inserted into the sheep produces the clotting protein in the sheep’s milk • This protein can then be given to hemophilia patients
Recombinant DNA in Agriculture • Crops that stay fresh longer and are more resistant to disease • Plants resistant to herbicide so weeds can be killed easier • Higher product yields or higher in vitamins • Peanuts and soybeans that don’t cause allergic reactions
Section 2 Review • How are transgenic organisms different from natural organisms of the same species? • How are sticky ends important in making recombinant DNA? • How does gel electrophoresis separate fragments of DNA? • What is a restriction enzyme? • What is PCR? • Explain two ways in which recombinant bacteria are used for human applications. • Many scientists consider engineering to be simply an efficient method of selective breeding. Explain.
The Human Genome • In 1990, scientists in the U.S. organized the Human Genome Project (PGP) • An international effort to completely map and sequence the human genome • Approximately 20,000 - 25,000 genes on 46 chromosomes • In February, 2001, the PGP published its working draft of the 3 billion base pairs in most human cells • Mini-lab, page 350 (as a class)
Linkage Maps • Crossing over occurs • Geneticists use the frequency of crossing over to map the relative position of genes on a chromosome • Genes that are further apart are more likely to have crossing over occur
Linkage Mapping • Suppose there are 4 genes on a chromosome – A, B, C, D • Frequencies of recombination as follows: • Between A & B: 50% (50 map units) • Between A & D: 10% (10 map units) • Between B & C: 5% (5 map units) • Between C & D: 35% (35 map units) • These give a relative distance between genes • A -10 units- D -35units- C -5 units- B (whole thing is 50 units)
Linkage Mapping • The problem with this in humans, is that we have relatively few offspring • Geneticists mark genes that have specific sequences • They can follow these through inheritance and hopefully see what it does • If a gene is marked, not passed on and that trait doesn’t show up, it may help identify the gene
Sequencing the Human Genome • Genome is cloned, cut into segments, and then run through gel electrophoresis • Arrange the fragments and get a sequence • Machines can do this much faster
Applications of HGP • Probably the biggest application so far has been the identification of genetic disorders • Often done prenatal • Take cells from amniotic fluid and look for deviations
Gene Therapy • The insertion of normal genes into human cells to correct genetic disorders • Have been used for SCID (severe combined immunodeficiency syndrome), cystic fibrosis, sickle-cell anemia, hemophilia and others. • Scientists are hopeful his will help treat cancer, heart disease, AIDS and many other things.
DNA Fingerprinting • Genes are separated by segments of noncoding DNA (“junk DNA”) • These segments produce distinct combinations of patterns unique to each individual • What are the uses?
DNA Fingerprinting • Small DNA sample obtained • Clone samples with PCR • Cut into fragments • Separated by gel electrophoresis • Chances of two identical matches are infinitesimally small
Stem Cells • An undifferentiated cell • Doesn’t have a specific function yet • Will eventually become differentiated • It will get a specific function and then can only do certain thins • GSLC site
Other Uses of DNA Technology • Look at mummies to understand them • Looked at Abraham Lincoln’s hair • Look at fossils and compare extinct species • They now seem unlimited. • Is that a good thing?
Section 3 Review • What is the Human Genome Project? • Compare a linkage map and a sequencing map. • What is the goal of gene therapy? • Explain why DNA fingerprinting can be used as evidence in law enforcement. • Describe some possible benefits of the Human Genome Project