Section 15.3Studying the Human Genome

I Can…

• ETS 2.1 I can conduct, analyze, and interpret a biotechnology investigation (gel electrophoresis, transformation, etc.)

Key Questions

1. How can scientists read DNA base sequences?

2. How large is the human genome?

Vocabulary

• Restriction enzyme

• Gel electrophoresis

• Genomic imprinting

Manipulating DNA

• Scientists can now read DNA base sequences by…

1. Cutting DNA

2. Separating DNA

3. Reading DNA

4. Assembling the Sequence

1. Cutting DNA

• DNA is easy to extract from cells. However, DNA molecules are so large, they must be cut into smaller pieces for analysis.

• In the late 1960s, scientists discovered natural enzymes, called restriction enzymes, that could cut DNA at specific sites.

2. Separating DNA

• Gel electrophoresis is used to separate DNA fragments.

• DNA is negatively charged.

• The smaller the DNA fragment, the faster and farther it moves.

• The current is turned off after a few hours.

• Stains make the bands visible.

• Researchers can remove individual fragments to study them.

3. Reading DNA

3. Reading DNA

• Until the late 1980s, DNA sequencing was a slow process, prone to errors, and very expensive.

• Sequencing has been improved in recent years.

• Tasks that once took a person a year to do can now be done in a few hours.

4. Assembling the Sequence

• Shotgun sequencing• Chromosomes are cut into fragments

• The fragments are sequenced and the information is fed into a computer

• Computer aligns matching fragments to come up with a single, complete sequence

Polymerase Chain Reaction (PCR)

• Used to make multiple copies of a gene

• Useful when only tiny amounts of DNA are available

• Uses DNA polymerase enzyme from bacteria found in hot springs in Yellowstone National Park

Polymerase Chain Reaction (PCR)

1. DNA is heated to

separate strands.

2. The mixture is cooled and

primers bind to the strands.

3. DNA polymerase

adds nucleotides to

strands, producing

two complementary

strands.

4. The process repeats and the

section of DNA is copied again.

Each cycle doubles the amount

of DNA.

The Human Genome

• The Human Genome Project finished the first complete human DNA sequence in 2003.

• It marked the beginning of a new era of research on human molecular genetics.

• Labs are now studying…• Which regions are DNA are transcribed into RNA?

• Which bind to proteins?

• Which are marked with epigenetic tags?

• Which vary from one individual to the next?

How Many Genes?

• Human cells contain approximately 20,000 genes (3 billion bases).

• Only about 2% of our DNA actually codes for proteins.

• We still do not know the functions of about 25% of our genes.

The Large and Small of It

• “Somewhere between a chicken and a grape”…

• Chicken genome = 17,000 genes

• Grape genome = 30,000 genes

The Personal Genome

• Most of our DNA will match base for base with each other.

• On average, 1 base in 1200 will not match between two individuals.

• These single base differences are called SNPs (single nucleotide polymorphisms).

• Some of these SNPs are associated with certain traits, including certain diseases and medical conditions.

• High-speed DNA sequencing is making it possible for physicians to tailor medical treatments to the patient’s genome.

Genome Privacy

• In 2008, U.S. Congress passed the Genetic Information Nondiscrimination Act.• Makes it illegal for insurance companies and employers to discriminate based

on info from genetic tests.

Gene Imprinting

• Genomic imprinting- epigenetic chemical marks can be attached to DNA and histone proteins in a way that affect gene expression by altering chromatin structure

• Some of these marks can be passed down through either the mother or father

• These marks silence the gene • Nearly 100 genes in humans are imprinted in this way

• Example- Angelman syndrome• Deletion of gene UBE3A on chromosome 15• Causes seizure and unusually happy disposition

Angelman Syndrome

Section 15.3 Exit Ticket

1. How are restriction enzymes used to digest DNA?

2. What is the function of gel electrophoresis?

The End