13-1 Changing the Living World
Selective Breeding
Selective breeding allows only those organisms with desired characteristics to produce the next generation.
Nearly all domestic animals and most crop plants have been produced by selective breeding.
Humans use selective breeding to pass desired traits on to the next generation of organisms.
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Hybridization
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Hybridization is the crossing of dissimilar individuals to bring together the best of both
organisms.
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Hybrids, the individuals produced by such crosses, are often hardier than either of the
parents.
Inbreeding
• Inbreeding is the continued breeding of individuals with similar characteristics.
• Inbreeding helps to ensure that the characteristics that make each breed unique will be
preserved.
• Serious genetic problems can result from excessive inbreeding.
Increasing Variation
Breeders increase the genetic variation in a population by inducing mutations.
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Mutations occur spontaneously, but breeders can increase the mutation rate by using radiation and
chemicals.
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Breeders can often produce a few mutants with desirable characteristics that are not found in the
original population.
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Producing New Kinds of Bacteria
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Introducing mutations has allowed scientists to develop hundreds of useful bacterial strains,
including:
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bacteria that can clean up oil spills
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bacteria that break down plastic
Polyploid Examples
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Potatoes – Tetraploid
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Sugar Cane – Octoploid
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Wheat – Hexaploid
13-2 Manipulating DNA
The Tools of Molecular Biology
Scientists use different techniques to:
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extract DNA from cells
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cut DNA into smaller pieces
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identify the sequence of bases in a DNA molecule
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make unlimited copies of DNA
In genetic engineering, biologists make changes in the DNA code of a living organism.
DNA Extraction
DNA can be extracted from most cells by a simple chemical procedure.
The cells are opened and the DNA is separated from the other cell parts.
Cutting DNA
Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using
restriction enzymes.
Each restriction enzyme cuts DNA at a specific sequence of nucleotides.
Separating DNA
In gel electrophoresis, DNA fragments are placed at one end of a porous gel, and an electric voltage is
applied to the gel.
Gel Electrophoresis
First, restriction enzymes cut DNA into fragments.
The DNA fragments are poured into wells on a gel.
An electric voltage is applied to the gel.
The smaller the DNA fragment, the faster and farther it will move across the gel.
Making Copies
Polymerase chain reaction (PCR) is a technique that allows biologists to make copies of genes.
Small amounts of DNA can be multiplied making it easier to analyze.
Made possible by an enzyme found in a bacterium living in hot springs in Yellow Stone National Park.