Based on my prior knowledge of soybean cultivation, the Thousand Seed Weight (MHG) is a crucial factor that affects grain yield. The relationship between MHG and grain yield can be analyzed as follows:

1. **Low grain yield**: For soybean cultivars with low grain yield, the MHG values tend to be lower. This is because a lower thousand seed weight indicates smaller and potentially lighter seeds, which may result in lower yield.

2. **High grain yield**: Conversely, soybean cultivars with high grain yield typically have higher MHG values. A higher thousand seed weight indicates larger and potentially heavier seeds, which can contribute to a higher yield.

Here is the dictionary containing possible MHG values for each target class:

```json
{
	"low": [10.4, 9.7, 8.9, 11.2, 9.5],
	"high": [13.8, 12.5, 14.1, 13.2, 12.9]
}
```

Please note that the values provided are just examples and may not reflect the specific range of values in the dataset you are working with.