end show slide 1 of 18 copyright pearson prentice hall 13-1 changing the living world

Copyright Pearson Prentice Hall

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13-1 Changing the Living World


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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.


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Selective Breeding

Humans use selective breeding to pass desired traits on to the next generation of organisms.


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Selective Breeding

Hybridization

________________________________ is the crossing of dissimilar individuals to bring together the best of both organisms.

Hybrids, the individuals produced by such crosses, are often hardier than either of the parents.

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Selective Breeding

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.


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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______________

_________________________.

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

Introducing mutations has allowed scientists to develop hundreds of useful bacterial strains, including bacteria that can clean up oil spills.


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Producing New Kinds of Plants

Mutations in some plant cells produce cells that have double or triple the normal number of chromosomes.

This condition, known as polyploidy, produces new species of plants that are often larger and stronger than their diploid relatives.

Polyploidy in animals is usually fatal.

Except in the case of the Red Viscacha Rat


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13-2 Manipulating DNA


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Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules.

The Tools of Molecular Biology


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Scientists use different techniques to:

• extract DNA from cells

• cut DNA into smaller pieces

• identify the sequence of bases in a DNA molecule

• make unlimited copies of DNA


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In_______________________, biologists make changes in the DNA code of a living organism.


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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.


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Cutting DNA

Most DNA molecules are too large to be analyzed, so biologists cut them into smaller fragments using restriction enzymes.


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Each ________________________cuts DNA at a specific sequence of nucleotides.

Recognition sequences

DNA sequence

Restriction enzyme EcoR I cuts the DNA into fragments

Sticky end


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A restriction enzyme will cut a DNA sequence only if it matches the sequence precisely.

Recognition sequences

DNA sequence

Restriction enzyme EcoR I cuts the DNA into fragments

Sticky end


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Separating DNA

In___________________________, DNA fragments are placed at one end of a porous gel, and an electric voltage is applied to the gel.

When the power is turned on, the negatively-charged DNA molecules move toward the positive end of the gel.

Whoa! We did this!!!!!!


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Gel electrophoresis can be used to compare the genomes of different organisms or different individuals.

It can also be used to locate and identify one particular gene in an individual's genome.


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DNA plus restriction enzyme

Mixture of DNA fragments

Gel

Power source

Gel Electrophoresis

Longer fragments

Shorter fragments


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First, restriction enzymes cut DNA into fragments.

The DNA fragments are poured into wells on a gel.

DNA plus restriction enzyme

Mixture of DNA fragments

Gel

Gel Electrophoresis


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An electric voltage is applied to the gel. This moves the DNA fragments across the gel.

The smaller the DNA fragment, the faster and farther it will move across the gel.

Power source

Gel Electrophoresis


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Based on size, the DNA fragments make a pattern of bands on the gel.

These bands can then be compared with other samples of DNA.

Longer fragments

Shorter fragments

Gel Electrophoresis


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Using the DNA Sequence


Knowing the sequence of an organism’s DNA allows researchers to study specific genes, to compare them with the genes of other organisms, and to try to discover the functions of different genes and gene combinations.


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Reading the Sequence

In DNA sequencing, a complementary DNA strand is made using a small proportion of fluorescently labeled nucleotides.


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DNA Sequencing

DNA strand with unknown base sequence

DNA fragments synthesized using unknown strand as a template

Dye molecules


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Each time a labeled nucleotide is added, it stops the process of replication, producing a short color-coded DNA fragment.

When the mixture of fragments is separated on a gel, the DNA sequence can be read.


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Base sequence as “read” from the order of the dye bands on the gel from bottom to top:

T G C A CElectrophoresis gel


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Cutting and Pasting

Short sequences of DNA can be assembled using DNA synthesizers.

“Synthetic” sequences can be joined to “natural” sequences using enzymes that splice DNA together.


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These enzymes also make it possible to take a gene from one organism and attach it to the DNA of another organism.

Such DNA molecules are sometimes called recombinant DNA.


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Making Copies

________________________________________

is a technique that allows biologists to make copies of genes.

A biologist adds short pieces of DNA that are complementary to portions of the sequence.


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DNA is heated to separate its two strands, then cooled to allow the primers to bind to single-stranded DNA.

DNA polymerase starts making copies of the region between the primers.

• PCR song: http://www.youtube.com/watch?v=7uafUVNkuzg

• DNA Song: http://www.youtube.com/watch?v=-bF2QalUj1Y


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DNA heated to separate strands

PCR cyclesDNA copies

1 2 3 4 5 etc.1 2 4 8 16 etc.

Polymerase Chain Reaction (PCR)

DNA polymerase adds complementary strand

DNA fragment to be copied

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