Module 3
Looping through DNA
Applying loops to biological sequences.
Counting bases
Now let's use a loop for something biological. Count how many times the base A appears in a sequence.
Python
seq = "ATGCGCA"
count_a = 0
for base in seq:
if base == "A":
count_a = count_a + 1
print(count_a)→ 2
The loop visits each base. The if statement checks whether it is A. If so, the counter increases. After the loop, count_a holds the answer.
Your task
Count A bases
- Loop through ATGCGCA and count how many times A appears. Print the count.
Biology connection
This pattern, visiting each element and counting matches, is fundamental in bioinformatics. You will use it constantly.