Advanced Forensic Biology: Glossary

This dataset measures gene expression from various human tissues.

Gene expression is measured from the hybridization of mRNA molecules to microarray probes.

Some tissues have genes that are uniquely or strongly expressed in them which makes them gene-markers of that tissue.

Finding tissue-specific markers can be done through several methods: PCA, clustering or even custom ones.

Computing several descriptive metrics and distribution plots is important to visualise value distributions and potential outliers.

Scaling is necessary to visualise values that show value differences of several order of magnitude.

A pairwise plot matrix can help to pinpoint samples with similar gene expression profiles.

Scaling of expression values is essential for distance calculation and hierarchical clustering.

The clustering method of choice can have a profound impact

Although clustering is a powerful technique to describe data structure, it does not easily help to pinpoint at specific interesting genes.

Sometimes, creating a new variable is a necessary step to find interesting leads in a dataset.

Data transformation that converts a distribution to a normal one can benefit to one’s analysis.

Several biaises including sequencing depth can result in analysis artifacts and must be corrected trough scaling/normalisation.