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deepvariant-model-training.md

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Training DeepVariant models

It is possible to train your own DeepVariant models with the released DeepVariant code. By training your own models you can potentially teach DeepVariant to call variants better on your specific sequencing data than the stock released model. It is often possible to greatly increase the accuracy of DeepVariant on new data types, particularly if these look significantly different from the deep whole-genome Illumina sequencing data used to train the stock model, such as exomes or targeted capture or other sequencing technologies.

Unfortunately, the Genomics team does not have the capacity to support setting up, running, or evaluating training new models for DeepVariant. That said, the following high-level overview should help bootstrap training your own custom models or fine-tune the released model on new datasets:

  • Run make_examples in training mode, providing the --confident_regions and --truth_variants' arguments so thatmake_examples` produces the labeled TensorFlow examples uses during training. Confident regions and truth variants should be a BED file of regions where variants (or not) have been confidently determined and a VCF file containing all of the variants within those regions. Genome in a Bottle provides examples of such files.
  • Prepare a config text protobuf pointing to the output of make_examples, which looks something like:
name: "my-training-dataset"
tfrecord_path: "/path/to/my/training_examples.tfrecord"
num_examples: 42

  • Setup a machine or machines to use with TensorFlow for training. We recommend either a distributed configuration or a single machine with a large training capacity (multiple GPUs or TPUs) as many millions of training steps are required to produce high-quality models. Less are required for fine-tuning an existing model to a new dataset, though.

  • Training the model is accomplished with the model_train.py script; check the source code of this file for required arguments and options. A key argument is --dataset_config_pbtxt, which should point to the dataset config proto create above, and is used by model_train.py to feed labeled data into TensorFlow for model training. Another key argument is --start_from_checkpoint, which tells the training system to start not from a random parameter set but to initialize the model with the parameters from the provided model.

    We often use two pre-trained models to start DeepVariant training. (a) The imagenet inception_v3 checkpoint from Slim, which we use for training models "from scratch". (b) The released DeepVariant model itself, in order to "fine-tune" the DeepVariant model for your own dataset.

It should be possible, to verify everything is setup correctly, to (1) make some labeled examples using the WGS case study data on chr20 (2) start up model_train.py, it's companion model_eval.py, and TensorBoard on a single machine with a GPU and (3) interact with TensorBoard to get a sense of how training DeepVariant models works.

Once this is working, it's a matter of scaling up the training to realistic datasets and steps. The Genomics team trains DeepVariant using a distributed TensorFlow training cluster to roughly ~10 million steps (with a batch size of 64, meaning we train on 640M pileup tensors in a standard training run). We then select a few high-quality models within those steps using TensorBoard and QC them for their actual calling performance.

We recommend you read through the general TensorFlow documentation on training models to better understand how this all works and fits together: