Chapter 13 Genetics and Biotechnology 13.1 Applied Genetics

Applied Genetics Selective breeding is used to produce organisms with desired traits. Dog breeds Plants Hybridization Time consuming Expensive Inbreeding Two closely related organisms are bred to have the desired traits and to eliminate the undesired ones in future generations

Inbreeding Advantage – desired traits are passed on Disadvantage – harmful recessive traits can be passed on Increases the chance of homozygous recessive offspring: if both parents carry the recessive allele, the harmful trait likely will not be eliminated.

Test Cross Involves breeding an organism that has the unknown genotype with one that is homozygous recessive for the desired trait. If the parent’s genotype is homozygous dominant, all the offspring will have the dominant phenotype; if it is heterozygous, the offspring will show a 1:1 phenotypic ratio.

Section 13.2: DNA Technology Researchers use genetic engineering to manipulate DNA Genetic engineering – technology that involves manipulating the DNA of one organism in order to insert exogenous DNA (the DNA of another organism). Example: GFP- green fluorescent protein Some fish – neons may contain GFP GFP – found in jellyfish

DNA Tools Genome: an organisms total DNA present in the nucleus of each cell The Human Genome – can contain millions and millions of nucleotides DNA tools can be used to manipulate DNA and to isolate genes from the rest of the genome Restriction enzymes – proteins that recognize and bind to specific DNA sequences and cleave the DNA within that sequence

DNA Tools A restriction enzyme is also called an endonuclease It cuts the viral DNA into fragments after it enters the bacteria Restriction enzymes are used as powerful tools for isolating specific genes or regions of the genome When the restriction enzyme cleaves genomic DNA, it creates fragments of different sizes that are unique to every individual

DNA Tools EcoRI – cuts DNA containing the sequence GAATTC The end of the DNA fragments created by EcoRI are called sticky ends because they contain single-stranded DNA that is complementary Figure 13.4 on page 364 Sticky ends are important because they can be joined together with other DNA fragments that have complementary sticky ends

DNA Tools Not all restriction enzymes create sticky ends Some enzymes produce fragments containing blunt ends Blunt ends do not have regions of single- stranded DNA and can join to any other DNA fragment with blunt ends

DNA Tools Gel electrophoresis – an electric current is used to separate the DNA fragments according to the size of the fragment The smaller fragments move farther faster When the loaded gel is placed in an electophoresis tank and the electric current is turned on, the DNA fragments separate Page 365 – see Figure 13.5

Recombinant DNA Technology When DNA fragments have been separated by gel electophoresis, fragments of a specific size can be removed from the gel and combined with DNA fragments from another source This newly generated DNA molecule, with DNA from different sources, is called recombinant DNA.

Recombinant DNA Technology A carrier, called a vector, transfers the recombinant DNA into a bacterial cell called the host cell. Plasmids and viruses – commonly used as vectors Plasmids – small, circular, double-stranded DNA molecules that occur naturally in bacteria and yeast cells – used as vectors because they can be cut with restriction enzymes

Recombinant DNA Technology Figure 13.6 on page 366 DNA ligase – an enzyme normally used by cells for DNA repair and replication, joins the two DNA fragments chemically (both sticky and blunt ends) Once complete, recombinant plasmid DNA molecules can be inserted into a host cell and more can be made

Recombinant DNA Technology Gene cloning To make large amounts of recombinant plasmid DNA, bacterial cells are mixed with recombinant plasmid DNA This can happen through a process called transformation Figure 13.7 on page 367 After transformation occurs, replication of bacteria results in a process called cloning

Recombinant DNA Technology DNA sequencing The sequence of the DNA nucleotides of most organisms is unknown Knowing the sequences of an organism’s DNA or of a cloned DNA fragment provides valuable information for scientists Can be used to: predict function of a gene To compare genes Identify mutations or errors in sequence

Recombinant DNA Technology Figure 13.8 on page 368 DNA can be sequenced using fluorescent- tagged nucleotides Polymerase chain reaction – a process used to make millions of copies of a specific region of a DNA fragment PCR – extremely sensitive and can detect a single DNA molecule in a sample and can then be copied or amplified Figure 13.9 page 369 – steps of PCR

Steps of Polymerase Chain Reaction Step 1: DNA fragment to be copied, DNA polymerase, four DNA nucleotides and two short single-stranded pieces of DNA called primers are placed in a tube The primers are complementary to the ends of the DNA fragment that will be copied and used as starting points for DNA synthesis PCR begins when the tube is heated

Steps of Polymerase Chain Reaction Step 2: Heat separates the two strands of the template DNA fragment When tube is cooled, the primers can bind to each strand of the template DNA Thermocycler – automated machine used to cycle the tube containing all the components used in PCR through hot and cold temperatures

Steps in Polymerase Chain Reaction Step 3: Each primer binds to one strand of the DNA fragment Once primers are bound, DNA polymerase incorporates the correct nucleotides between the two primers Process of heating, cooling, and nucleotide incorporation is repeated 20 to 40 times = millions of copies of original fragment Used by researchers in labs, forensic scientists and doctors

Genetic Engineering Table 13.1 page 370 Restriction enzymes Gel electophoresis Recombinant DNA technology Gene cloning DNA sequencing Polymerase chain reaction (PCR) Procedures often include: cleavage by a restriction enzyme, isolation of fragments, combination with exogenous DNA, cloning or PCR and identification of sequences

Biotechnology The use of genetic engineering to find solutions to problems Transgenic organisms: organisms that are genetically engineered by inserting a gene from another organism Transgenic organisms (plants, animals, bacteria) are used for research, medical and agricultural purposes

Transgenic Animals Mice, fruit flies, and roundworms widely used in research labs around the world to study diseases and develop ways to treat them Some transgenic livestock have been produced to improve the food supply and human health Transgenic goats used to secrete a protein used to prevent human blood from clotting during surgery Transgenic chickens and turkeys are being produced that are resistant to disease Transgenic fish are engineered to grow faster In future, may be used as a source of organs for organ transplants.

Biotechnology Transgenic plants: many species have been genetically altered to be more resistant to insect or viral pests Examples: soybeans, corn, cotton, canola Being tested: sweet potatoes, bananas(for vaccines) Transgenic bacteria: Insulin, growth hormones and substances that dissolve blood clots are made from transgenic bacteria Transgenic bacteria are also used to clean up oil spills, decompose garbage and protect crops from frost damage