# Predicting the functional impact of single nucleotide variants in Drosophila melanogaster with FlyCADD

## TL;DR

FlyCADD is a tool that predicts how single nucleotide variants affect the function of genes in fruit flies, helping researchers understand genetic impacts on traits and evolution.

## Contribution

FlyCADD is a novel functional impact prediction tool for single nucleotide variants in Drosophila melanogaster, integrating over 650 genomic features.

## Key findings

- FlyCADD integrates over 650 genomic features to predict the functional impact of single nucleotide variants in Drosophila.
- The tool is effective for ranking phenotype-associated variants and refining CRISPR-Cas9 experimental design.
- FlyCADD improves genotype–phenotype understanding by providing impact scores for any single nucleotide variant in D. melanogaster.

## Abstract

Understanding how genetic variants drive phenotypic differences is a major challenge in molecular biology. Single nucleotide polymorphisms form the vast majority of genetic variation and play critical roles in complex, polygenic phenotypes, yet their functional impact is poorly understood from traditional gene-level analyses. In-depth knowledge about the impact of single nucleotide polymorphisms has broad applications in health and disease, population genomic, and evolution studies. The wealth of genomic data and available functional genetic tools make Drosophila melanogaster an ideal model species for studies at single nucleotide resolution. However, to leverage these resources for genotype–phenotype research and potentially combine it with the power of functional genetics, it is essential to develop techniques to predict functional impact and causality of single nucleotide variants. Here, we present FlyCADD, a functional impact prediction tool for single nucleotide variants in D. melanogaster. FlyCADD, based on the Combined Annotation-Dependent Depletion (CADD) framework, integrates over 650 genomic features—including conservation scores, GC content, and DNA secondary structure—into a single metric reflecting a variant's predicted impact on evolutionary fitness. FlyCADD provides impact prediction scores for any single nucleotide variant on the D. melanogaster genome. We demonstrate the power of FlyCADD for typical applications, such as the ranking of phenotype-associated variants to prioritize variants for follow-up studies, evaluation of naturally occurring polymorphisms, and refining of CRISPR-Cas9 experimental design. FlyCADD provides a powerful framework for interpreting the functional impact of any single nucleotide variant in D. melanogaster, thereby improving our understanding of genotype–phenotype connections.