In genetics, "PI" can refer to two distinct concepts:
1. Nucleotide Diversity (π)
In population genetics, π (pi) represents nucleotide diversity. It's a measurement of genetic variation within a population. Specifically, it quantifies the average number of nucleotide differences between any two randomly selected DNA sequences from that population. This measure is useful for understanding the level of genetic diversity within a species or population, which can be related to factors like adaptation and disease resistance.
- Calculation: π is calculated by comparing all possible pairs of sequences within a sample and averaging the differences.
- Significance: High π suggests a diverse gene pool, while low π indicates limited diversity.
- Applications: Nucleotide diversity is used in various fields, including evolutionary biology, conservation genetics, and disease research.
Several sources confirm this definition:
- Wikipedia's Nucleotide Diversity page describes π as "a concept in molecular genetics which is used to measure the degree of polymorphism within a population."
- This York University workshop defines nucleotide diversity (π) as "the average pairwise difference between all possible pairs of individuals in your sample."
- A study on low nucleotide diversity in humans utilizes π to analyze human genetic variation.
2. Primary Immunodeficiency (PI)
In immunology, PI stands for Primary Immunodeficiency. This refers to a group of disorders where the body's immune system is compromised due to genetic defects. These defects can affect different parts of the immune system, leading to increased susceptibility to infections.
- Genetic Basis: PI is often inherited and can follow different inheritance patterns (autosomal recessive, autosomal dominant, or X-linked recessive).
- Diagnosis: Family history and genetic testing are crucial for diagnosis.
- Symptoms: Symptoms vary widely depending on the specific type of PI. They can range from recurrent infections to severe, life-threatening illnesses.
The following sources support this definition:
- The CDC's page on Primary Immunodeficiency states that "People with primary immunodeficiency (PI) have an immune system that doesn't work correctly. PI often has a genetic cause and runs in families."
- The Immune Deficiency Foundation explains that "PI conditions are caused by genetic variants and can affect anyone, regardless of age, gender, or ethnicity."
- An article on genetic testing for PI highlights the importance of genetic testing in PI diagnosis.
