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Variables

2 min read • Verified October 2026 • Peer-Reviewed Learning Resource
Tested Stacks: GATK 4.6.1 Samtools 1.21 Nextflow 24.10 Seurat v5.1 Python 3.12
Prerequisites: Basic Linux CLI & Sequencing Formats
📚 Chapter 1 of 6 0% Course Completed

Variables are used to store information that can be later accessed and manipulated. The information stored in a variable can be a number, a string of characters, or even a complex data structure such as a list or a dictionary.

 

In biology, variables can be used to store data about biological organisms, such as their name, age, weight, and so on. They can also be used to represent different things in a biological experiment, such as the independent variable, the dependent variable, and the controlled variables.

 

To create a variable in Python, you need to choose a name for it and assign a value to it using the “=” operator. For example, you could create a variable called “age” and assign it the value 25 like this:

 

age = 25

 

Once you have created a variable, you can use it in your program by referring to its name. For example, you could print the value of the “age” variable like this:

 

print(age)

 

This would output the number 25 to the console.

 

Variables can also be used in mathematical expressions. For example, you could create two variables called “x” and “y” and use them in a calculation like this:

Pyton
				x = 10
y = 5
result = x + y
print(result)

This will output 15 to the console.

 

Variables can also be used to store strings of text. For example, you could create a variable called “name” and assign it the value “Tomato” like this:

Pyton
				name = "Tomato"
print(name)

Once you have created the variable, you can use it in your program just like any other variable.

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Common Pitfalls & Troubleshooting Checklist

  • Java Heap Exhaustion (GATK / Picard): If processes terminate with java.lang.OutOfMemoryError, set your environment variable explicitly: export _JAVA_OPTIONS="-Xmx16g -Djava.io.tmpdir=/tmp".
  • Index Timestamp Mismatch: If tools complain that a BAM index is missing or out of date, regenerate with samtools index -@ 4 sample.bam.
  • Conda Channel Conflicts: Avoid ABI incompatibilities between bioconda and conda-forge by setting strict priority: conda config --set channel_priority strict.
  • Chromosome Naming Contamination: Always verify whether reference FASTA headers use chr1 or 1; divergent naming causes silent alignment drops.
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