1. Got Milk? SNPs, Inheritance, and the Evolution of Lactose Tolerance

2. Lactose Intolerance?

3. What’s Happening Digestive System

4. The Genetics Tolerance is a mutation in the LCT gene (Chromosome 2) Everyone has two copes of each gene (maternal and paternal) Each gene has a C or a T at a specific location – This is called a SNP (single nucleotide polymorphism) – TT and TC = tolerant – CC = intolerant What is an SNP?What is an SNP? Video

5. The Genetics Chromosome 2 from dad Chromosome 2 from mom LCT T T The individual is lactose TOLERANT

6. The Genetics Chromosome 2 from dad Chromosome 2 from mom LCT T C The individual is lactose TOLERANT

7. The Genetics Chromosome 2 from dad Chromosome 2 from mom LCT C C The individual is lactose INTOLERANT

8. Where is it most prevalent? Prevalence of lactose tolerance and reliance on dairy products vary throughout the world.

9. Why do we see this pattern? Map shows % intolerance

10. Natural Selection 1.There is variation of traits in a population 2. There is differential reproduction. 3.There is heredity. 3.End result.

11. How can we see this in our genes? PCR (polymerase chain reaction – Build copies of the segment that contains the SNP so we can see it What’s in the mix? – Master Mix: Taq, dNTPs, buffer – Primer Mix: 4 primers (two outer primers and two inner primers) PCR Reaction Video The inner primers tell you your genotype

12. Molecular Cell Biology, Lodish et. al. 4th ed. DNA Replication

13. The “PCR Building Blocks” A “dNTP mix” contains equal amounts of : dATP dTTP dGTP dCTP Deoxynucleotide-triphosphates: dNTPs

14. The PCR “Cycle” Denature: 94-96 o C… Anneal: 37-65 o C… Extension: 72 o C… Repeat steps 1-3: Separates double helix into two strands Primers bind to target site on single stranded DNA DNA polymerase adds dNTPs according to the base pairing rules (polymerization) 5 to 40 times using a Thermal Cycler

15. Cycle 1 Cycle 2 Cycle 3 After 30 cycles, DNA is amplified over a billion-fold! Target sequence

16. Cellular DNA Replication PCR vs. Cellular DNA Replication

17. Tetra-primer ARMS-PCR Procedure for SNPs

18. Agarose Gel Electrophoresis

19. Dye is added to give the DNA color DNA “Ladder” well #1 well #2 well #3 + _ large DNA fragments small DNA fragments Electron micrograph of an agarose gel Agarose Gel Electrophoresis

20. The Tetra-Primer System It’s not super “clean” You get primer dimers Inner primers are similar and stick together Ignore them on the gel (they’re smaller than 100 bp) The outer primers are sometimes non-specific The fragments are small! Run the gel for the full time to separate out the bands!

21. Sample Gel: Focus on the “lac” Lane

22. How to Interpret the Gel Primer dimers <100 Inner band: 135 (faint) Inner band: 188 Outer band- 268 Extraneous bands at 400, 500