Based on prior knowledge and the given feature description, the Thousand seed weight (MHG) is a numeric variable that represents the weight of a thousand seeds in grams. To analyze the relationship between MHG and the grain yield of the soybean cultivar, we can consider the following:

1. Higher MHG values might indicate larger and heavier seeds, which could potentially lead to a higher grain yield.
2. Lower MHG values might indicate smaller and lighter seeds, which could potentially result in a lower grain yield.

To create the dictionary with specific details, let's assume the following typical MHG values for the target classes 'low' and 'high':

```json
{
	"low": [32.5, 33.2, 34.1, 34.7, 35.0],
	"high": [38.6, 39.2, 40.5, 41.1, 42.0]
}
```

These values are arbitrary and should be adjusted based on domain knowledge and the specifics of the dataset when conducting a real analysis.