How to Determine the GC‐Content of a DNA Sequence

The guanine-cytosine content, or GC-content, of a DNA sequence indicates the percentage of nucleotide base pairs where guanine is bonded to cytosine. DNA with a higher GC-content will be harder to break apart.

Method 1
Method 1 of 2:
By Hand

  1. Image titled 7114843 1
    1
    Trace through the sequence and tally the number of cytosine (C) or guanine (G) nucleotides.
  2. Image titled 7114843 2
    2
    Divide the number of cytosine and guanine nucleotides by the total number of base pairs in the sequence.
    Advertisement

Method 2
Method 2 of 2:
Programmatically (Python 2)

  1. Image titled 7114843 3
    1
    Create or accept an input file. This article assumes that the input is in FASTA format, with a single sequence per file.
  2. Image titled 7114843 4
    2
    Read in the file. For FASTA format:
    • Discard the first line of the file.
    • Remove all remaining newlines and other trailing whitespace.
    def init(sequence):
    with open(argv[1]) as input:
        sequence = "".join([line.strip() for line in input.readlines()[1:]])
    return sequence
  3. Image titled 7114843 5
    3
    Create a counter. Iterate through the data and increment your counter as you encounter any guanine or cytosine nucleotides.
    4. 4
    def GCcontent(sequence):
    GCcount = 0
    for letter in sequence:
        if letter == "G" or letter == "C":
            GCcount += 1
    return GCcount
  4. Image titled 7114843 6
    5
    Divide the GC count by the total length of the sequence, and output the result in percentage format.
    Advertisement
    5. 6
    def main():
    script, input = argv
    sequence = ""
    sequence = init(sequence)
    print "%.2f" % (float(GCcontent(sequence)) / len(sequence))

You Might Also Like

Find the Reverse Complement of a DNA Sequence
How to
Find the Reverse Complement of a DNA Sequence
Start Programming in Python
How to
Start Programming in Python
Create Loops in Python
How to
Create Loops in Python
Install Python
How to
Install Python
Determine Your Baby's Blood Type Using a Punnett Square
How to
Determine Your Baby's Blood Type Using a Punnett Square
Predict Your Baby's Eye Color
How to
Predict Your Baby's Eye Color
Make a Punnett Square
How to
Make a Punnett Square
Calculate LOD Score
How to
Calculate LOD Score
Read Gel Electrophoresis Bands
How to
Read Gel Electrophoresis Bands
Determine Genotype
How to
Determine Genotype
Get a DNA Test
How to
Get a DNA Test
Extract Banana DNA
How to
Extract Banana DNA
Use a Punnett Square to Do a Monohybrid Cross
How to
Use a Punnett Square to Do a Monohybrid Cross
Understand DNA Structure
How to
Understand DNA Structure
Advertisement

About This Article

wikiHow is a “wiki,” similar to Wikipedia, which means that many of our articles are co-written by multiple authors. To create this article, volunteer authors worked to edit and improve it over time. This article has been viewed 9,242 times.
2 votes - 100%
Co-authors: 2
Updated: May 6, 2021
Views: 9,242
Categories: Genetics
Advertisement