Provide a brief description of the variable gene activity hypothesis as it relates to development. What information is often provided in support of this hypothesis?

Because all cells apparently have the same genetic information, yet may differ
structurally and functionally, the variable gene activity hypothesis suggests that differential gene transcription (genetic regulation) accounts for such cellular
diversity. Evidence in support of this model includes the following:
chromosome puffs, isozymes, and the presence of genes but no gene products in some tissues (hemoglobin, for example).