Pure breeding is the artificial selection of identical individuals that, when crossed, always produce offspring of the same phenotype.

Transcription

1 Selective Breeding Selective breeding is choosing only plants and animals with desirable characteristics to reproduce. It is artificial selection that guides the evolution of species for human purposes. Pure breeding is the artificial selection of identical individuals that, when crossed, always produce offspring of the same phenotype. Domestication is the taming/selective breeding of animals and plants for human purposes.

2 Selective Breeding Induced Nondisjunction Hybridization is selective breeding individuals of a different phenotype, variety, or species. Hybridization has been used in agriculture to produce crop species, like tomato plants that are hardier, with increased yield and tomatoes that are larger, redder, juicier, and more flavorful. The typical result of hybridization between closely related animal species is offspring that are sterile (not fertile), like Mules, Ligers, Tigons, Jaglions, Wholphins, Beefalo, Camas, Zorses, etc...

3 Selective Breeding Inbreeding is the reproduction of closely related individuals. It is often done during selective breeding to produce a pure breed. Excessive inbreeding decreases variation in populations and increases the frequency of recessive phenotypes, because closely related individuals are more likely to carry the same recessive alleles. A population bottleneck is an event that drastically reduces the size of a population due to environmental disaster, hunting, or habitat destruction. The rebounding population will show decreased variation due to inbreeding. This is a form of genetic drift. Low genetic diversity in natural populations can be dangerous. For example, all individuals are more likely to be susceptible to a particular disease. The Cheetah population today shows little genetic variation, possibly due to a population bottleneck in their evolutionary past, resulting from disease (Feline Immunodeficiency Virus (FIV).

4 Increasing Variation Wild Ancestor (2N) Induced Nondisjunction Diploid Gametes! The ultimate source of genetic diversity (new genes) is mutation (gene & chromosomal). Organisms with unique, desirable traits have been produced by inducing gene mutations with chemicals or radiation. For example, bacteria have been developed that can digest oil and help clean up oil spills. Polyploidy is the condition of having more than 2 sets of chromosomes (greater than diploid). The induction of the polyploid state has been used in agriculture to produce, for example, strawberries that are much larger than their wild ancestor. Polyploid plants often grow larger, produce more or larger fruit and are hardier. Polyploidy in animals is usually FATAL. Polyploid (4N) Plant

5 Tools: DNA Extraction Genetic engineering is the modification of the characteristics of an organism by manipulating its genetic material. DNA extraction is the isolation of DNA from the nucleus of cells. DNA can be extracted from any cell or tissue. The cell lysis buffer is simply dish detergent. It works to lyse cells because, like grease on dishes, cellular membranes are composed of lipid. Protease is a hydrolytic enzyme that breaks the peptide bonds between amino acids in proteins. The protease/salt solution breaks down cellular proteins. The solution is incubated at 50 o C because that is the optimum temperature for protease activity. Note that meat tenderizer will work! A precipitate is a substance that is deposited in solid form from a solution. DNA dissolves in aqueous solution, but it is not soluble in ice-cold alcohol, so it precipitates.

6 Tools: PCR 95 C Denaturation C Primers Anneal 72 C Polymerase Extension REPEAT! Polymerase chain reaction (PCR) is a technique used to make multiple copies of a sequence of DNA. PCR is very precise and can be used to amplify (copy) a specific target sequence from a mixture of DNA. Similar to DNA replication! DNA primers are short DNA polynucleotides that provide a 3 end for DNA polymerase to add nucleotides to. They are specific for, and bracket the DNA sequence of interest. Thermocycling is the precise, continuous cycling of temperature by a thermocycler. Warming causes the polynucleotides of the DNA double helix to denature (unzip). Cooling allows for the annealing (binding) of DNA primers, then warming promotes DNA polymerase activity (extension) REPEAT! For every turn of the cycle, the amount of DNA doubles! Ingredients 1) DNA Sequence to copy 2) DNA Primers (specific) 3) DNA Polymerase (special) 4) DNA Nucleotides

7 Tools: Restriction Enzymes Recognition sequences Restriction Site Restriction Site DNA sequence Restriction enzyme EcoR I cuts the DNA into fragments Sticky end Restriction enzymes act as an immune system against bacteriophages in prokaryotes. They cut VERY SPECIFIC DNA sequences in a VERY SPECIFIC way. A SPECIFIC recognition sequence is recognized by the enzyme and the DNA is cut at the SPECIFIC restriction site between two nucleotides on both DNA strands. Depending on the restriction site, the DNA may be cut straight across, or staggered producing sticky ends that are complementary to, and can reanneal with any DNA fragment cut with the SAME RESTRICTION ENZYME. Remember this for genetic engineering!

8 DNA plus restriction enzyme Mixture of DNA fragments Gel Power source Tools: Gel Electrophoresis This is all under aqueous buffer solution. Longer fragments Shorter fragments Restriction Fragment Length Polymorphisms Gel electrophoresis is a technique for separating proteins or DNA fragments according to size and charge. DNA obtained by DNA extraction is treated with restriction enzymes prior to running on a gel. The gel is made of highly purified agarose (agar, from algae), the same substance used to culture bacteria, or polyacrylamide. Both are semi-solids (gel) composed of mostly water, and are porous, so molecules are able to migrate through. The purpose of the power source and electrodes are to establish an electric field across the gel which causes the negatively charged DNA to migrate toward the positively charged anode. As a mixture of DNA fragments migrates through the gel, smaller fragments travel faster than larger fragments. This results in the separation of fragments according to length. Sources of DNA samples include any cells or tissue. This technique can be used to identify and purify proteins, identify genes (genetic testing), sequence DNA, identify individuals (DNA fingerprint), determine relationships between people (paternity test), and between species!