LESSON 9 Analyzing DNA Sequences and DNA Barcoding

LESSON 9: Analyzing DNA Sequences and DNA Barcoding Power. Point slides to accompany Using Bioinformatics: Genetic Research

How DNA Sequence Data is Obtained for Genetic Research Obtain Samples: Blood , Saliva, Hair Follicles, Feathers, Scales Genetic Data Compare DNA Sequences to One Another Extract DNA from Cells Sequence DNA …TTCACCAACAGGCCCACA… TTCAACAACAGGCCCAC TTCACCAACAGGCCCAC TTCATCAACAGGCCCAC GOALS: • Identify the organism from which the DNA was obtained. • Compare DNA sequences to each other. Image Source: Wikimedia Commons

Overview of DNA Sequencing Mix with primers Perform sequencing reaction DNA Sample …T T C A C C A A C T G G C C C A… DNA Sequence Chromatogram

Sequence Both Strands of DNA Sequence #1: Top Strand Sequence #2: Bottom Strand A T G A C G G A T C A G C Sequence #1: Top Strand T A C T G C C T A G T C G Sequence #2: Bottom Strand Image Source: Wikimedia Commons

Compare the Two Sequences Sequence #1: Top Strand Sequence #2: Bottom Strand Sequence #1: Top (“F”) 5’- A T G A C G G A T C A G C – 3’ Sequence #2: Bottom (“R”) 3’- T A C T G C C T A G T C G – 5’ Bioinformatics tools like BLAST can be used to compare the sequences from the two strands. Image Source: Wikimedia Commons

Viewing DNA Sequences with Finch. TV Image Source: Finch. TV

DNA Peaks Can Vary in Height and Width Image Source: Finch. TV

Quality Values Represent the Accuracy of Each Base Call Quality values represent the ability of the DNA sequencing software to identify the base at a given position. Quality Value (Q) = log 10 of the error probability * -10. Q 10 means the base has a one in ten chance (probability) of being misidentified. Q 20 = probability of 1 in 100 of being misidentified. Q 30 = probability of 1 in 1, 000 of being misidentified. Q 40 = probability of 1 in 10, 000 of being misidentified.

Quality Values Are Used When Comparing Sequences Quality values represent the ability of the DNA sequencing software to identify the base at a given position. Image Source: Finch. TV

Background “Noise” May Be Present Image Source: Finch. TV

The Beginning and Ends of Sequences Are Likely To Be Poor Quality Image Source: Finch. TV

Examples of Chromatogram Data #1 #2 #3 Circle #1: Example of a series of the same nucleotide (many T’s in a row). Notice the highest peaks are visible at each position. Circle #2: Example of an ambiguous base call. Notice the T (Red) at position 57 (highlighted in blue) is just below a green peak (A) at the same position. Look at the poor quality score on bottom left of screen (Q 12). An A may be the actual nucleotide at this position. Circle #3: Example of two A’s together. The peaks look different, but are the highest peaks at these positions. Image Source: Finch. TV

Transcription and Translation Begin at the Start Codon Reading Frame +1 Sequence #1: 5’- Sequence #2: 3’- M T D Q A T G A C G G A T G A G C T A C T G C C T A C T C G – 3’ – 5’

There Are Six Potential Reading Frames in DNA Reading Frame +3 Reading Frame +2 Reading Frame +1 Sequence #1: 5’- M T D Q A T G A C G G A T G A G C T A C T G C C T A C T C G Sequence #2: 3’Reading Frame -1 Reading Frame -2 Reading Frame -3 – 3’ – 5’

Frame-Shifts, Amino Acid Changes, and Stop Codons Reading Frame +2 5’- M D G STOP A T G G A C G G A T G A G – 3’ Accidental insertion of an extra “G” when editing Reading Frame +1 Sequence #1: 5’- Sequence #2: 3’- M T G E A T G A C G G A T G A G C T A C T G C C T A C T C G – 3’ – 5’