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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

Genetic Technology

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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

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  • 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”

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  • 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

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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?

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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?

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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

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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

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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

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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

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  • 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

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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

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  • Mini-Lab 13.1

    • Page 343

  • Modeling Recombinant DNA

    • Page 354

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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

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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

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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?

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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

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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

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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

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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

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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

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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

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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

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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.

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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)

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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

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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)

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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

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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

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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

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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.

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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?

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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

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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

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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?

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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