Transcript Chapter 14: Human Inheritance

Section 14-3:
Studying the Human Genome
Manipulating DNA
 The SMALLEST human chromosome contains 50
million bases
 DNA is a HUGE molecule that is difficult to
manipulate
 In the 1970s, scientists discovered they could use
natural enzymes to analyze DNA
 Today, scientists read DNA base sequences by using
enzymes to cut, separate, and replicate DNA base by
base
Cutting DNA
 Easy to extract/separate DNA from other
macromolecules
 In order to analyze, DNA molecules must be cut into
smaller pieces
 Restriction enzymes are produced by bacteria – they
cut DNA molecule at specific sequences of nucleotides
into precise pieces called restriction fragments
 Hundreds of Res, each cuts at different sequence
Cutting DNA
 Ex: EcoRI recognizes GAATTC
 Cuts between G and A bases, leaving “sticky ends”
 Can bond to complementary bases
Separating DNA
 Gel electrophoresis is used to separate DNA fragments
that have been cut with restriction enzymes
 Can then analyze DNA in pieces
 Steps:
 Mixture of DNA fragments placed at the end of a pourous gel
 Electric voltage applied to gel, causing DNA molecules to
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move toward positive end (DNA has a neg charge)
Smaller DNA fragments move faster/farther
Creates a banding pattern
Stains used to make bands visible
Remove fragments and study
Reading DNA
 Read = sequence
 Single-stranded DNA put in test tube with DNA
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polymerase and four bases (ATGC)
DNA polymerase uses unknown strand as template to make
new strands
Some of the added bases have dyes attached,
Each time a labeled base is added, replication stops
End up with a series of fragments that are color coded
Separate fragments with electrophoresis, colored bands on
the gel tell exact sequence of bases on DNA
Automated
The Human Genome Project
 Began in 1990 – US and several other countries
 Goals:
 Sequence all 3 billion base pairs of human DNA
 Identify all human genes
 Sequence genomes of model organisms to interpret
human genome
 Develop new technology to support research
 Explore gene functions
 Study human variation
 Train future scientists
The Human Genome Project
 How they did it:
 Break genome into pieces
 Sequence pieces, identify markers
 Used computer for analysis
 Current research explores data gained from HGP –
looking for genes, identifying their function
Comparing Sequences
 Most of every person’s DNA is the same
 On average, one base in every 1200 with not match
 These are called SNPs (single nucleotide
polymorphisms)
 Collections of SNPs are called halpotypes – haploid
gentoypes
 Project called HapMap began in 2002 to indentify all
the haplotypes
Sharing Data
 Copies of human/other genomes available on the
internet
 New field borne – bioinformatics
 Combines molecular biology with information science
 Also new field called genomics – the study of whole
genomes, including genes and their functions
What have we learned?
 Complete working copy of human genome in 2000
 Full reference sequence in 2003
 Contains 3 billion nucleotide bases
 Only 2% encodes for proteins
 Found genes/sequences associated with
diseases/disorders
 Identified 3 million locations of SNPs
 New technologies, medical applications