Single Nucleotide Polymorphisms Mrs Stewart Medical Interventions Central

Single Nucleotide Polymorphisms Mrs. Stewart Medical Interventions Central Magnet School

Review • Why is Taq polymerase used in PCR instead of other DNA polymerases?

Objective • Use laboratory techniques such as DNA extraction, PCR, and restriction analysis to identify single base pair differences in DNA • Explain how single base pair changes called single nucleotide polymorphisms (SNPs) can be identified through genetic testing and often correlate to specific diseases or traits.

Single Nucleotide Polymorphisms • The parts of the human genome that vary by just a single nucleotide • Abbreviated as SNPs • Pronounced as “snips”

Reflect • Explain what a SNP is in your own words in your journal

Effect of SNPs • Non-coding DNA regions = no effect • Genes that code for proteins = potentially changing the protein produced E F F E C T – Different phenotypes – Disease/disorder

Think – Pair - Share • How does a single base change a protein?

Remember: • a change in DNA can lead to a change in a protein • If the protein plays a role in keeping you healthy, serious consequences may occur.

Using a Single Nucleotide Polymorphism to Predict Bitter Tasting Ability Lab Overview

Gene of Interest • TAS 2 R 38 • On chromosome #7 • Ability to taste “bitter”

What is your phenotype? Non. Taster Weak Taster Strong Taster

Step 1: Isolate a sample of your DNA from your cheek cells

Step 2: Amplifying the Gene of Interest • Using your DNA sample, you will amplify a 220 base pair region of the PTC gene using PCR. – Specific primers attach to either side of the target sequence

SNPs for TAS 2 R 38 gene • In this lab, you will investigate one of the base pair changes or single nucleotide polymorphisms (SNPs) that affects a person’s ability to taste the chemical PTC.

Genetics Review – Question 1 • The inability to taste PTC is a recessive trait. • If a capital “T” is is used to designate the dominant allele and a lowercase “t” is used to designate the recessive allele, what is the genotype of a “Nontaster”?

Answer • A “Nontaster” carries two recessive alleles and thus has the genotype “tt”.

Genetics Review – Question 2 • What are the possible genotypes for a “Taster”?

Answer • A “Taster” may be homozygous dominant with a genotype of “TT” or heterozygous with a genotype of “Tt”. • In this lab, you will use the tools of molecular biology to determine your genotype for PTC tasting.

Step 3: Restriction Analysis • Restriction enzymes, molecular scissors, recognize specific DNA sequences and cut the nucleotide strands. • In this part of the experiment, you will use a specific restriction enzyme, Hae. III, to identify a SNP or base pair difference in the amplified segment of the PTC tasting gene.

Hae. III and TAS 2 R 38 gene • Hae. III restriction enzyme – 5’ GGCC – 3’ CCGG 5’ ---GG 3’ ---CC CC--- 3’ GG--- 5’ • TAS 2 R 38 gene variations NONTASTER (t) TASTER (T) GGCGGGCACT CCGCCCGTGA GGCGGCCACT CCGCCGGTGA

Step 4: Gel Electrophoresis • Gel Electrophoresis separates DNA fragments based on their molecular weight. • Once you have digested your DNA sample with the restriction enzymes, run your product on a gel to analyze your results.

What will gel results show? Non-taster Taster