Bellwork What do humans commonly use selective breeding

Bellwork: What do humans commonly use selective breeding for? Are there any issues associated with it’s use?

In today’s class • We will look at different forms of selective breeding • Advantages and disadvantages • How scientists make and combine DNA fragments • How scientists incorporate DNA into other organisms • Transgenic plants and animals • Cloning

Selective Breeding Section 15. 1

What is selective breeding? • Selective breeding takes advantage of naturally occurring genetic variation, to pass wanted traits on to the next generation of organisms

Selective breeding doesn’t just apply to animals…. • Corn lost the ability to survive in the wild but gained many valuable agricultural traits • Hard case around kernels for example disappeared

Hybridization • The crossing of dissimilar individuals together to bring together the best of both organisms • Hybrids (the offspring of these crosses) are often hardier than their parents • American Botanist Luther Burbank was a pioneer of hybridization in the late 1800 s • Combined properties such as disease resistance and fruit productivity

Inbreeding • Inbreeding is the continued breeding of individuals with similar characteristics • Why you have pedigree dogs • Dog show winners can be very valuable • Animals can be used as stud animals • Often successful racehorses or award winning cattle

How do you counteract some of the problems associated with selected breeding? • The wide variation found in natural populations of species makes selective breeding possible • Genetic variation can be increased by breeders by incorporating mutations, which are a source of biological diversity • When scientists manipulate the genetic make up of an organism they are using biotechnology • Biotechnology is the application of a technological process, invention or method to living organisms • Selective breeding is a form of biotechnology

Bacterial mutations • Breeders can affect the mutation rate by using radiation or chemicals • Many mutations can be harmful • Others can be very beneficial • Produce useful characteristics not usually found in the population • This technique works very well with bacteria • As they are so small, millions can be ‘treated’ at the same time • Allowed scientists to produce useful strains of bacteria • Bacteria for cleaning up oil spills • Scientists working on bacteria to clean up radiation or metal pollution

Polyploid plants • When chromosome do not separate properly during meiosis • In plants – can produce many useful characteristics • Polyploidy is fatal in animals • In plants, produces many traits that breeders want to utilize

Summary • Selective breeding is widely utilized to reinforce certain characteristics of animals and plants • Explains dog breeds • Explains why we have cultivated crops different to wild varieties • Hybridization - the crossing of individuals with contrasting characteristics • Inbreeding – the reinforcing of characteristics within a population • Bacterial mutations – have the potential to be very useful in society • Polpyploid plants are often utilized by breeders to incorporate useful traits into a gene pool

Recombinant DNA Section 15. 2

Copying DNA of living organisms • Until recently breeders could only work with variations that occur in nature • Now it is possible to go a step further, and certain genes can be transferred between organisms • Finding specific genes on the DNA molecule is hard • Like finding a needle in a haystack • Solution – magnet • Similar approach to working with DNA

Finding the genes • Douglas Prasher in 1987 wanted to identify the genes in jellyfish that make them glow green (the gene that codes for Green Fluorescent Protein (GFP)) • He thought the GFP could be linked to when the protein was being made in the cell • Like attaching a lightbulb to that molecule • Prasher studied the amino acid sequence of the protein • • Using a genetic code table he predicted the m. RNA base sequence He then used a complimentary base sequence to attract an m. RNA that matched his predictions He then checked, and found that this m. RNA occurred naturally in jellyfish He then found the gene, by taking a gel with restriction fragments of jellyfish DNA • One fragment bound to the m. RNA • This fragment contained the gene for GFP

Southern Blotting

Polymerase Chain Reaction • Technique used to make many copies of a gene • DNA polymerase enzyme first shown to be able to withstand heating and cooling cycles in bacteria from hotsprings of Yellowstone national park

How is the recombinant DNA used? • Is it possible to change the DNA of a living cell? • Griffith with his mice and bacteria experiments showed this was already possible

How can DNA fragments be combined? • DNA can be built in a lab, and inserted into cells • First step is to build the DNA sequence in a lab with the genes you want to include in the cell • DNA synthesizers produce short pieces of DNA up to several hudred bases in length • Sequences can be joined using enzymes such as DNA ligase that splices DNA together • Recombinant DNA is the joining of DNA from two or more sources, makes it possible to change the genetic composition of an organism

Plasmids and genetic markers • Initially there were problems with cells copying or replicating the new DNA • Nowadays Recombinant DNA is added to another piece of DNA that contains a ‘start’ signal – ensuring it is copied • Bacteria often contain plasmids – small circular DNA molecules • DNA is joined to a plasmid which then transforms the bacteria • Genetic marker allows transformed bacteria to be visible • Transformed bacteria can also have antibiotic resistance added so you are just left with a population of modified bacteria • Why is this process so useful?

Transgenic organisms • These involved incorporating genes from different species • Recombinant DNA is inserted into the genome of the host organism • Transgenic technology was perfected on mice • Possible to transform plants and animals • Increased our understanding of gene regulation and expression • Transgenic plants • Plants transformed using agrobacterium • In nature this bacterium contains plasmids that cause tumors • This tumor causing plasmid can be replaced with recombinant DNA • Transgenic animals • • Animals can be transformed with some of the same techniques as plants DNA can be injected into the nucleus of egg cells Enzyme already there can help insert DNA into foreign cell Nowadays gene replacement also possible – sequences of a chromosome can be replaced

Cloning • A clone is a member of a population of genetically identical cells produced from a single cell • A new individual is grown from a single cell from an adult organism • Cloning bacteria is easy, but multicelled organisms are harder • Cloned tadpoles first produced in 1952 • Dolly the sheep was cloned in 1997