Which is NOT a primary developmental process?
Classical developmental biology defines four overlapping processes: growth via cell proliferation and size increase, pattern formation establishing body axes and positional information through morphogen gradients like Sonic hedgehog and BMP, morphogenesis shaping tissues through cell movement and adhesion, and differentiation producing specialized cell types. Migration in mammalian development often considered component of morphogenesis rather than separate primary category in Gilbert classification. Some textbooks include migration as part of morphogenesis alongside growth and differentiation. Therefore migration alone generally not listed as independent primary process compared with other three core pillars plus differentiation.
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 4: Primary developmental processes.