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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

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chapter 13

Chapter 13

Genetic Technology

selective breeding
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
  • 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”
  • 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
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
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
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
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
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 enzymes10
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
  • 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
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
  • Mini-Lab 13.1
    • Page 343
  • Modeling Recombinant DNA
    • Page 354
gene cloning
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
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
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
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
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
recombinant dna in industry
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
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
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 animals25
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
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
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
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
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
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
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
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
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
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 fingerprinting36
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
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
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
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